Here are collected a number of abstracts relating to brain function and through which we can identify the GENERAL IDM processes at work. The 'dimension of precision' is reflected in such work as that on map-making (hippocampus studies) and left/right hemisphere differences in general.
ABSTRACTS
==============
Psychosom Med. 2003 Jul-Aug;65(4):564-70. Related Articles, Links
Alterations in brain and immune function produced by mindfulness meditation.
Davidson RJ, Kabat-Zinn J, Schumacher J, Rosenkranz M, Muller D, Santorelli SF, Urbanowski F, Harrington A, Bonus
K, Sheridan JF.
Laboratory for Affective Neuroscience (R.J.D., J.S., M.R.), Department of Psychology, University of Wisconsin,
Madison, Wisconsin.
OBJECTIVE: The underlying changes in biological processes that are associated with reported changes in mental and
physical health in response to meditation have not been systematically explored. We performed a randomized, controlled
study on the effects on brain and immune function of a well-known and widely used 8-week clinical training program
in mindfulness meditation applied in a work environment with healthy employees. METHODS: We measured brain electrical
activity before and immediately after, and then 4 months after an 8-week training program in mindfulness meditation.
Twenty-five subjects were tested in the meditation group. A wait-list control group (N = 16) was tested at the
same points in time as the meditators. At the end of the 8-week period, subjects in both groups were vaccinated
with influenza vaccine. RESULTS: We report for the first time significant increases in left-sided anterior activation,
a pattern previously associated with positive affect, in the meditators compared with the nonmeditators. We also
found significant increases in antibody titers to influenza vaccine among subjects in the meditation compared with
those in the wait-list control group. Finally, the magnitude of increase in left-sided activation predicted the
magnitude of antibody titer rise to the vaccine. CONCLUSIONS: These findings demonstrate that a short program in
mindfulness meditation produces demonstrable effects on brain and immune function. These findings suggest that
meditation may change brain and immune function in positive ways and underscore the need for additional research.
<IDM : additional work focused by Richardson shows prefrontal cortext activity influences immune system - gets into the differences of our consciousness-nature that allows us to feedback IMAGINED states to elicit body activity (and so a proactive perspective) vs our more reactive species-nature>
=============
J Abnorm Psychol. 2002 Nov;111(4):676-81.
Frontal brain asymmetry in restrained eaters.
Silva JR, Pizzagalli DA, Larson CL, Jackson DC, Davidson RJ.
Psychobiology Department, Complutense University, Madrid, Spain.
It is well known that the eating patterns that restrain chronic dieters (restrained eaters) can be disinhibited
by anxiety, which in turn has been associated with relative right frontal brain activity in independent electroencephalographic
(EEG) studies. Combining these two lines of evidence, the authors tested the hypothesis that chronic restrained
eating is associated with relative right frontal asymmetry. Resting anterior brain asymmetry and self-reported
measures of anxiety and depression were collected in 23 restrained and 32 unrestrained eaters. As hypothesized,
groups differed in tonic frontal activity, with restrained eaters showing more relative right frontal activity.
Furthermore, relative right frontal activity was associated with greater self-reported restraint. Right-sided prefrontal
asymmetry may thus represent a diathesis associated with increased vulnerability toward restrained eating.
============
Arch Gen Psychiatry. 2003 Aug;60(8):789-96.
Life event dimensions of loss, humiliation, entrapment, and danger in the prediction of onsets of major depression
and generalized anxiety.
Kendler KS, Hettema JM, Butera F, Gardner CO, Prescott CA.
Virginia Institute for Psychiatry and Behavioral Genetics, Medical College of Virginia of Virginia Commonwealth
University, Richmond, USA.
BACKGROUND: Although substantial evidence suggests that stressful life events predispose to the onset of episodes
of depression and anxiety, the essential features of these events that are depressogenic and anxiogenic remain
uncertain. METHODS: High contextual threat stressful life events, assessed in 98 592 person-months from 7322 male
and female adult twins ascertained from a population-based registry, were blindly rated on the dimensions of humiliation,
entrapment, loss, and danger and their categories. Onsets of pure major depression (MD), pure generalized anxiety
syndrome (GAS) (defined as generalized anxiety disorder with a 2-week minimum duration), and mixed MD-GAS episodes
were examined using logistic regression. RESULTS: Onsets of pure MD and mixed MD-GAS were predicted by higher ratings
of loss and humiliation. Onsets of pure GAS were predicted by higher ratings of loss and danger. High ratings of
entrapment predicted only onsets of mixed episodes. The loss categories of death and respondent-initiated separation
predicted pure MD but not pure GAS episodes. Events with a combination of humiliation (especially other-initiated
separation) and loss were more depressogenic than pure loss events, including death. No sex differences were seen
in the prediction of episodes of illness by event categories. CONCLUSIONS: In addition to loss, humiliating events
that directly devalue an individual in a core role were strongly linked to risk for depressive episodes. Event
dimensions and categories that predispose to pure MD vs pure GAS episodes can be distinguished with moderate specificity.
The event dimensions that preceded mixed MD-GAS episodes were largely the sum of those that preceded pure MD and
pure GAS episodes.
<IDM - Slots into the position of SADNESS in the IDM mapping of emotions>
===========================
Published online before print June 5, 2003
Proc. Natl. Acad. Sci. USA, 10.1073/pnas.0732061100
Neuroscience
Reset of human neocortical oscillations during a working memory task
D. S. Rizzuto *, J. R. Madsen , E. B. Bromfield ¶, A. Schulze-Bonhage ||, D.
Seelig *, R. Aschenbrenner-Scheibe ||, and M. J. Kahana ***
*Volen Center for Complex Systems, Brandeis University, Waltham, MA 02454;
Department of Neurosurgery, Children's Hospital, Boston, MA 02115; Department
of Surgery, Harvard Medical School, Boston, MA 02115; ¶Department of Neurology,
Brigham and Women's Hospital, Boston, MA 02115; and ||Neurozentrum,
Universitaet Freiburg, D-79106 Freiburg, Germany
Communicated by Saul Sternberg, University of Pennsylvania, Philadelphia, PA,
April 8, 2003 (received for review May 22, 2002)
Both amplitude and phase of rhythmic slow-wave electroencephalographic activity
are physiological correlates of learning and memory in rodents. In humans,
oscillatory amplitude has been shown to correlate with memory; however, the
role of oscillatory phase in human memory is unknown. We recorded intracranial
electroencephalogram from human cortical and hippocampal areas while subjects
performed a short-term recognition memory task. On each trial, a series of four
list items was presented followed by a memory probe. We found agreement across
trials of the phase of oscillations in the 7- to 16-Hz range after randomly
timed stimulus events, evidence that these events either caused a phase shift
in the underlying oscillation or initiated a new oscillation. Phase locking in
this frequency range was not generally associated with increased poststimulus
power, suggesting that stimulus events reset the phase of ongoing oscillations.
Different stimulus classes selectively modulated this phase reset effect, with
topographically distinct sets of recording sites exhibiting preferential reset
to either probe items or to list items. These findings implicate the reset of
brain oscillations in human working memory.
<IDM - oscillations and meaning derivation>
=============
Does the cerebellum contribute to specific aspects of attention?
Birgit Gottwald, , Zoran Mihajlovic, Barbara Wilde and Hubertus Maximilian Mehdorn
Neuropsychologia
Volume 41, Issue 11 , 2003, Pages 1452-1460
Abstract
We present data on attentional and neuropsychological functions of 16 patients with focal cerebellar lesions (13
tumours, 3 haematomas) compared to normative test data, and to 11 control subjects matched for age, gender, and
years of education. Patients showed distinct deficits in qualitative aspects of a divided attention task, and in
a working memory task. Performance in selective attention was unimpaired. The results support the concept that
the cerebellum plays a role not only in motor, but also in higher cognitive functions. They are discussed on the
basis of the idea that prediction and preparation are fundamental functions of the cerebellum. Therefore, the results
confirm the idea that cerebellar lesions lead to reduced performance in specific attention tasks.
<<IDM - gets into the issues of precision - dopamine shows ties to integration WITHIN a differentiation, linking of parts to assert a whole etc,fine motor control etc etc >>
=============
Conscious control over the content of unconscious cognition
Wilfried Kunde, Andrea Kiesel and Joachim Hoffmann
Cognition
Volume 88, Issue 2 , June 2003, Pages 223-242
Abstract
Visual stimuli (primes) presented too briefly to be consciously identified can nevertheless affect responses to
subsequent stimuli – an instance of unconscious cognition. There is a lively debate as to whether such priming
effects originate from unconscious semantic processing of the primes or from reactivation of learned motor responses
that conscious stimuli afford during preceding practice. In four experiments we demonstrate that unconscious stimuli
owe their impact neither to automatic semantic categorization nor to memory traces of preceding stimulus-response
episodes, but to their match with pre-specified cognitive action-trigger conditions. The intentional creation of
such triggers allows actors to control the way unconscious stimuli bias their behaviour.
<<IDM - our species-nature is not 'dumb' ;-) >>
=============
Dissociable neural systems for recognizing emotions
- Ralph Adolphs, Daniel Tranel and Antonio R. Damasio
Brain and Cognition
Volume 52, Issue 1 , June 2003, Pages 61-69
Abstract
This study tested the hypothesis that the recognition of emotions would draw upon anatomically separable brain
regions, depending on whether the stimuli were static or explicitly conveyed information regarding actions. We
investigated the hypothesis in a rare subject with extensive bilateral brain lesions, patient B., by administering
tasks that assessed recognition and naming of emotions from visual and verbal stimuli, some of which depicted actions
and some of which did not. B. could not recognize any primary emotion other than happiness, when emotions were
shown as static images or given as single verbal labels. By contrast, with the notable exception of disgust, he
correctly recognized primary emotions from dynamic displays of facial expressions as well as from stories that
described actions. Our findings are consistent with the idea that information about actions is processed in occipitoparietal
and dorsal frontal cortices, all of which are intact in B.'s brain. Such information subsequently would be linked
to knowledge about emotions that depends on structures mapping somatic states, many of which are also intact in
B.'s brain. However, one of these somatosensory structures, the insula, is bilaterally damaged, perhaps accounting
for B.'s uniformly impaired recognition of disgust (from both static and action stimuli). Other structures that
are damaged in B.'s brain, including bilateral inferior and anterior temporal lobe and medial frontal cortices,
appear to be critical for linking perception of static stimuli to recognition of emotions. Thus the retrieval of
knowledge regarding emotions draws upon widely distributed and partly distinct sets of neural structures, depending
on the attributes of the stimulus.
<<IDM -- see application to IDM page on emotions >>
=============
Brain Res Bull. 2003 May 30;60(4):387-93.
The evolution of mammalian cortex, from lamination to arealization.
Montagnini A, Treves A.
SISSA-Programme in Neuroscience, via Beirut 4, 34014, Trieste, Italy
We analyse some of the most important anatomical and functional features emerging at different stages of mammalian
brain evolution in terms of a possible computational advantage. At the transition from reptiles to mammals, a major
anatomical change occurs in the originally sensory dorsal cortex. The principal layer of pyramidal cells is split
by the insertion of a new layer of granule cells, giving rise to the laminated isocortex. It has been hypothesized
that this qualitative change in the evolution of mammalian brains is necessary to support fine topography in their
sensory maps. The simulation of neural network models demonstrates that a nonlaminated patch of cortex must compromise
between transmitting "where" information, explicitly mapped, topographically, on the cortical sheet,
and retrieving "what" information, represented by the distributed firing pattern across neurons. The
differentiation of a granular layer is shown in the model to yield a small quantitative advantage, allowing to
transmit a slightly better combination of both information types.Along the same theoretical lines, we are investigating
the multiplication of successive sensory areas coding for ever more composite stimuli, such as those in the visual
and auditory temporal cortices in primates. In particular we analyse the possible computational advantage for a
specific neural population devoted to encode the complex structure of whole stimuli, rather than relying on the
coactivation of separate populations encoding their basic elements.
(IDM focus - WHAT/WHERE as dogma)
==============
Cell. 2003 Feb 7;112(3):293-301.
Coding of sweet, bitter, and umami tastes: different receptor cells sharing similar signaling pathways.
Zhang Y, Hoon MA, Chandrashekar J, Mueller KL, Cook B, Wu D, Zuker CS, Ryba NJ.
Howard Hughes Medical Institute, Department of Biology, University of California, San Diego, La Jolla, CA 92093,
USA.
Mammals can taste a wide repertoire of chemosensory stimuli. Two unrelated families of receptors (T1Rs and T2Rs)
mediate responses to sweet, amino acids, and bitter compounds. Here, we demonstrate that knockouts of TRPM5, a
taste TRP ion channel, or PLCbeta2, a phospholipase C selectively expressed in taste tissue, abolish sweet, amino
acid, and bitter taste reception, but do not impact sour or salty tastes. Therefore, despite relying on different
receptors, sweet, amino acid, and bitter transduction converge on common signaling molecules. Using PLCbeta2 taste-blind
animals, we then examined a fundamental question in taste perception: how taste modalities are encoded at the cellular
level. Mice engineered to rescue PLCbeta2 function exclusively in bitter-receptor expressing cells respond normally
to bitter tastants but do not taste sweet or amino acid stimuli. Thus, bitter is encoded independently of sweet
and amino acids, and taste receptor cells are not broadly tuned across these modalities.
((IDM - sensory mapping of 'wholes')
==============
J Neurophysiol 2002 Jun;87(6):2715-25
Stimulus-related gamma oscillations in primate auditory cortex.
Brosch M, Budinger E, Scheich H.
Leibniz-Institut fur Neurobiologie, 39118 Magdeburg, Germany. brosch@ifn-magdeburg.de
With a multielectrode system, we explored neuronal activity in the gamma range (>40 Hz) in the primary and caudomedial
auditory cortex of six anesthetized macaque monkeys. Stimuli were tone bursts of 100- to 500-ms duration that were
presented at sound pressure levels of 40-60 dB and were varied over a wide range of frequencies. These stimuli
induced gamma oscillations, not phase-locked to the onset of stimulation, in 465 of 616 multiunit clusters and
at 321 of 422 sites at which field potentials were recorded. Occurrence of gamma activity was stimulus dependent.
It was mostly seen when the stimulus was at the units' preferred frequency. The incidence of gamma activity decreased
with increasing difference between stimulus frequency and preferred frequency. gamma activity emerged 100-900 ms
after stimulus onset with highest incidence ~120 ms. Amplitudes of stimulus-induced gamma oscillations in field
potentials were, on average, almost twice the amplitude of spontaneously occurring gamma oscillations. gamma activity
at different sites within the primary and the caudomedial auditory field could be synchronized at near-zero phase.
Synchrony depended on the spatial distance and on the receptive fields similarity of pairs of units. It decreased
with increasing distance between recording sites and increased with similarity of preferred frequencies of the
pairs of units. The results indicate that stimulus-induced gamma oscillations originate from sources in the auditory
cortex. They further suggest that gamma oscillations may provide a mechanism utilized in many parts of the sensory
cortex, including the auditory cortex, to integrate neurons according to the similarity of their receptive fields.
=============
International Journal of Bifurcation and Chaos, Vol. 13, No. 1 (2003) 7-18
WHEN TWO COUPLED PENDULUMS EQUAL ONE: A SYNCHRONIZATION MACHINE
H. J. T. SMITH
Department of Physics, University of Waterloo, Ontario, Canada
JAMES A. BLACKBURN
Department of Physics and Computing, Wilfrid Laurier University, Waterloo, Ontario, Canada
GREGORY L. BAKER
Division of Mathematics and Science, Bryn Athyn College of the New Church, Bryn Athyn, PA 19009, USA
We show that two coupled pendulums that are coupled and can synchronize, are mathematically equivalent to one "horizontal"
parametrically driven pendulum. We have fabricated a horizontal pendulum and present data from this horizontal
pendulum which we believe to be the first physical realization of such a mechanical "synchronization machine."
A description of intermittent synchronization that can occur when two coupled pendulums are in a chaotic state
is given in terms of the data from the horizontal pendulum. We discuss the relationship between the modes of the
horizontal pendulum and the corresponding synchronization of the two coupled pendulums. Finally, we show that when
a horizontal pendulum is driven by any random source, not necessarily chaotic, intermittent synchronization can
occur.
Keywords: Pendulum; synchronization; chaos.
(IDM - Hemisphere interactions, recursion scales)
=============
Brain Res Brain Res Rev 2002 Jun;39(1):1-28
The neurophysics of consciousness.
John ER.
Brain Research Laboratories, NYU School of Medicine, 550 First Avenue, New York 10016, USA. roy@br14.med.nyu.edu
Consciousness combines information about attributes of the present multimodal sensory environment with relevant
elements of the past. Information from each modality is continuously fractionated into distinct features, processed
locally by different brain regions relatively specialized for extracting these disparate components and globally
by interactions among these regions. Information is represented by levels of synchronization within neuronal populations
and of coherence among multiple brain regions that deviate from random fluctuations. Significant deviations constitute
local and global negative entropy, or information. Local field potentials reflect the degree of synchronization
among the neurons of the local ensembles. Large-scale integration, or 'binding', is proposed to involve oscillations
of local field potentials that play an important role in facilitating synchronization and coherence, assessed by
neuronal coincidence detectors, and parsed into perceptual frames by cortico-thalamo-cortical loops. The most probable
baseline levels of local synchrony, coherent interactions among brain regions, and frame durations have been quantitatively
described in large studies of their age-appropriate normative distributions and are considered as an approximation
to a conscious 'ground state'. The level of consciousness during anesthesia can be accurately predicted by the
magnitude and direction of reversible multivariate deviations from this ground state. An invariant set of changes
takes place during anesthesia, independent of the particular anesthetic agent. Evidence from a variety of neuroscience
areas supporting these propositions, together with the invariant reversible electrophysiological changes observed
with loss and return of consciousness, are used to provide a foundation for this theory of consciousness. This
paper illustrates the increasingly recognized need to consider global as well as local processes in the search
for better explanations of how the brain accomplishes the transformation from synchronous and distributed neuronal
discharges to seamless global subjective awareness.
=============
J Neurophysiol 2002 Apr;87(4):1993-2008
GABAergic and glutamatergic modulation of spontaneous and motor-cortex-evoked complex spike activity.
Lang EJ.
Department of Physiology and Neuroscience, New York University School of Medicine, New York, New York 10016, USA.
Lange01@popmail.med.nyu.edu
Olivocerebellar activity is organized such that synchronous complex spikes occur primarily among Purkinje cells
located within the same parasagittally oriented strip of cortex. Previous findings have shown that this synchrony
distribution is modulated by the release of GABA and glutamate within the inferior olive, which probably act by
controlling the efficacy of the electrotonic coupling between olivary neurons. The relative strengths of these
two neurotransmitters in modulating the patterns of synchrony were compared by obtaining multiple electrode recordings
of spontaneous crus 2a complex spike activity during intraolivary injection of solutions containing a GABA(A) (picrotoxin)
and/or AMPA [1,2,3,4-tetrahydro-6-nitro-2,3-dioxo-benzo[f]quinoxaline-7-sulfonamide disodium (NBQX)] receptor antagonist.
Injection of either antagonist led to increased synchrony between cells located within the same parasagittally
oriented approximately 250-microm-wide cortical strip. Picrotoxin also increased complex spike synchrony among
cells located in different cortical strips, leading to a less prominent banding pattern, whereas injections of
NBQX tended to decrease complex spike synchrony among such cells, enhancing the banding pattern. The relative strength
of these two classes of olivary afferents was assessed by first injecting one of the antagonists alone and then
in combination with the other. The enhanced banding pattern of complex spike synchrony following injection of NBQX
alone remained during the subsequent combined injection of both antagonists. Furthermore, the widespread synchronization
of complex spike activity following injection of picrotoxin alone was partially or completely reversed by combined
injection of picrotoxin and NBQX. Changes in the climbing fiber reflex induced by the intraolivary injections paralleled
the changes observed for spontaneous complex spike activity, indicating that the effects of picrotoxin and NBQX
on the synchrony distribution reflect changes in the pattern of effective coupling of inferior olivary neurons
and demonstrating that synchronous complex spike activity does not require simultaneous excitatory input to olivary
cells. Finally the pattern of synchrony during motor cortical stimulation was examined. It was found that the patterns
of synchrony for motor-cortex-evoked complex spike activity were similar to those of spontaneous activity, indicating
an important role for electrotonic coupling in determining the response of the olivocerebellar system to afferent
input. Moreover, intraolivary injections of picrotoxin increased the spatial distribution of the evoked response.
In sum, the results provide evidence for the hypothesis that electrotonic coupling of inferior olivary neurons
via gap junctions is the mechanism underlying complex spike synchrony and that this coupling plays an important
role in determining the responses of the olivocerebellar system to synaptic input.
=============
J Neurosci 2002 Feb 1;22(3):1002-9
Electrical synapses in the thalamic reticular nucleus.
Landisman CE, Long MA, Beierlein M, Deans MR, Paul DL, Connors BW.
Department of Neuroscience, Division of Biology and Medicine, Brown University, Providence, Rhode Island 02912,
USA.
Neurons of the thalamic reticular nucleus (TRN) provide inhibitory input to thalamic relay cells and generate synchronized
activity during sleep and seizures. It is widely assumed that TRN cells interact only via chemical synaptic connections.
However, we show that many neighboring pairs of TRN neurons in rats and mice are electrically coupled. In paired-cell
recordings, electrical synapses were able to mediate close correlations between action potentials when the coupling
was strong; they could modulate burst-firing states even when the coupling strength was more modest. Electrical
synapses between TRN neurons were absent in mice with a null mutation for the connexin36 (Cx36) gene. Surprisingly,
inhibitory chemical synaptic connections between pairs of neurons were not observed, although strong extracellular
stimuli could evoke inhibition in single TRN neurons. We conclude that Cx36-dependent gap junctions play an important
role in the regulation of neural firing patterns within the TRN. When combined with recent observations from the
cerebral cortex, our results imply that electrical synapses are a common mechanism for generating synchrony within
networks of inhibitory neurons in the mammalian forebrain.
=============
J Neurophysiol 2002 Mar;87(3):1526-41
Electrical coupling between model midbrain dopamine neurons: effects on firing pattern and synchrony.
Komendantov AO, Canavier CC.
Department of Psychology, University of New Orleans, New Orleans, LA 70148, USA.
The role of gap junctions between midbrain dopamine (DA) neurons in mechanisms of firing pattern generation and
synchronization has not been well characterized experimentally. We modified a multi-compartment model of DA neuron
by adding a spike-generating mechanism and electrically coupling the dendrites of two such neurons through gap
junctions. The burst-generating mechanism in the model neuron results from the interaction of a N-methyl-D-aspartate
(NMDA)-induced current and the sodium pump. The firing patterns exhibited by the two model neurons included low
frequency (2-7 Hz) spiking, high-frequency (13-20 Hz) spiking, irregular spiking, regular bursting, irregular bursting,
and leader/follower bursting, depending on the parameter values used for the permeability for NMDA-induced current
and the conductance for electrical coupling. All of these firing patterns have been observed in physiological neurons,
but a systematic dependence of the firing pattern on the covariation of these two parameters has not been established
experimentally. Our simulations indicate that electrical coupling facilitates NMDA-induced burst firing via two
mechanisms. The first can be observed in a pair of identical cells. At low frequencies (low NMDA), as coupling
strength was increased, only a transition from asynchronous to synchronous single-spike firing was observed. At
high frequencies (high NMDA), increasing the strength of the electrical coupling in an identical pair resulted
in a transition from high-frequency single-spike firing to burst firing, and further increases led to synchronous
high-frequency spiking. Weak electrical coupling destabilizes the synchronous solution of the fast spiking subsystems,
and in the presence of a slowly varying sodium concentration, the desynchronized spiking solution leads to bursts
that are approximately in phase with spikes that are not in phase. Thus this transitional mechanism depends critically
on action potential dynamics. The second mechanism for the induction of burst firing requires a heterogeneous pair
that is, respectively, too depolarized and too hyperpolarized to burst. The net effect of the coupling is to bias
at least one cell into an endogenously burst firing regime. In this case, action potential dynamics are not critical
to the transitional mechanism. If electrical coupling is indeed more prominent in vivo due to basal level of modulation
of gap junctions in vivo, these results may indicate why NMDA-induced burst firing is easier to observe in vivo
as compared in vitro.
=============
Neurosci Lett 2003 Jan 9;336(1):33-6
Scale-invariant fluctuations of the dynamical synchronization in human brain electrical activity.
Gong P, Nikolaev AR, van Leeuwen C.
Laboratory for Perceptual Dynamics, Riken, Brain Science Institute, 2-1, Hirosawa, Wako-shi, Saitama, 351-0198,
Japan. plgong@brain.riken.go.jp
The dynamical properties of large-scale, long-term phase synchronization behavior in the alpha range of electroencephalographic
signals were investigated. We observed dynamical phase synchronization and presented evidence of an underlying
spatiotemporal ordering. Fluctuations in the duration of episodes of intermittent synchrony are scale-invariant.
Moreover, the exponent used to describe this behavior is stable across different normal subjects. The results provide
a new feature of self-organization in human brain activity and constitute a quantitative basis for modeling its
dynamics.
===============
Epilepsia 2002 Jun;43(6):574-80
Cooling abolishes neuronal network synchronization in rat hippocampal slices.
Javedan SP, Fisher RS, Eder HG, Smith K, Wu J.
Division of Neurological Surgery, Barrow Neurological Institute, St. Joseph's Hospital and Medical Center, Phoenix,
Arizona 85013, USA.
PURPOSE: We sought to determine whether cooling brain tissue from 34 to 21 degrees C could abolish tetany-induced
neuronal network synchronization (gamma oscillations) without blocking normal synaptic transmission. METHODS: Intracellular
and extracellular electrodes recorded activity in transverse hippocampal slices (450-500 microm) from Sprague-Dawley
male rats, maintained in an air-fluid interface chamber. Gamma oscillations were evoked by afferent stimulation
at 100 Hz for 200 ms. Baseline temperature in the recording chamber was 34 degrees C, reduced to 21 degrees C within
20 min. RESULTS: Suprathreshold tetanic stimuli evoked membrane potential oscillations in the 40-Hz frequency range
(n = 21). Gamma oscillations induced by tetanic stimulation were blocked by bicuculline, a gamma-aminobutyric acid
(GABA)A-receptor antagonist. Cooling from 34 to 21 degrees C reversibly abolished gamma oscillations in all slices
tested. Short, low-frequency discharges persisted after cooling in six of 14 slices. Single-pulse-evoked potentials,
however, were preserved after cooling in all cases. Latency between stimulus and onset of gamma oscillation was
increased with cooling. Frequency of oscillation was correlated with chamber cooling temperature (r = 0.77). Tetanic
stimulation at high intensity elicited not only gamma oscillation, but also epileptiform bursts. Cooling dramatically
attenuated gamma oscillation and abolished epileptiform bursts in a reversible manner. CONCLUSIONS: Tetany-induced
neuronal network synchronization by GABAA-sensitive gamma oscillations is abolished reversibly by cooling to temperatures
that do not block excitatory synaptic transmission. Cooling also suppresses transition from gamma oscillation to
ictal bursting at higher stimulus intensities. These findings suggest that cooling may disrupt network synchrony
necessary for epileptiform activity.
(IDM FOCUS - consequences of variations in metabolic rates)
==============
Nature 2002 Nov 14;420(6912):168-71
Synchronization of animal population dynamics by large-scale climate.
Post E, Forchhammer MC.
Department of Biology, The Pennsylvania State University, 208 Mueller Lab, University Park, Pennsylvania 16802,
USA. esp10@psu.edu
The hypothesis that animal population dynamics may be synchronized by climate is highly relevant in the context
of climate change because it suggests that several populations might respond simultaneously to climatic trends
if their dynamics are entrained by environmental correlation. The dynamics of many species throughout the Northern
Hemisphere are influenced by a single large-scale climate system, the North Atlantic Oscillation (NAO), which exerts
highly correlated regional effects on local weather. But efforts to attribute synchronous fluctuations of contiguous
populations to large-scale climate are confounded by the synchronizing influences of dispersal or trophic interactions.
Here we report that the dynamics of caribou and musk oxen on opposite coasts of Greenland show spatial synchrony
among populations of both species that correlates with the NAO index. Our analysis shows that the NAO has an influence
in the high degree of cross-species synchrony between pairs of caribou and musk oxen populations separated by a
minimum of 1,000 km of inland ice. The vast distances, and complete physical and ecological separation of these
species, rule out spatial coupling by dispersal or interaction. These results indicate that animal populations
of different species may respond synchronously to global climate change over large regions.
===============
Biosystems 2002 Oct-Dec;67(1-3):139-46
Firing coincidences between neighboring retinal ganglion cells: inside information or epiphenomenon?
Levine MW, Castaldo K, Kasapoglu MB.
Department of Psychology, M/C 285, University of Illinois at Chicago, 1007 West Harrison Street, 60607, Chicago,
IL, USA
Retinal ganglion cells often fire impulses in synchrony; is this synchronization an irrelevant by-product of processing
shared inputs, or does it encode information? We examined the rate of occurrence of coincident impulses from pairs
of ganglion cells responding to stimuli that varied along several dimensions. We find that coincidences convey
little if any additional information about simple static stimuli beyond what could be determined from the firing
rates of the two cells considered separately. In fact, at least one of the separate cells generally provided a
better information channel than the coincidence rate, implying that under these conditions ganglion cells do not
employ a strategy of encoding by coincidences.
==============
J Neurosci 2002 Dec 15;22(24):10898-905
Rhythmicity without synchrony in the electrically uncoupled inferior olive.
Long MA, Deans MR, Paul DL, Connors BW.
Department of Neuroscience, Division of Biology and Medicine, Brown University, Providence, Rhode Island 02912,
USA.
Neurons of the inferior olivary nucleus (IO) form the climbing fibers that excite Purkinje cells of the cerebellar
cortex. IO neurons are electrically coupled through gap junctions, and they generate synchronous, subthreshold
oscillations of membrane potential at approximately 5-10 Hz. Experimental and theoretical studies have suggested
that both the rhythmicity and synchrony of IO neurons require electrical coupling. We recorded from pairs of IO
neurons in slices of mouse brainstem in vitro. Most pairs of neurons from wild-type (WT) mice were electrically
coupled, but coupling was rare and weak between neurons of knock-out (KO) mice for connexin36, a neuronal gap junction
protein. IO cells in both WT and KO mice generated rhythmic membrane fluctuations of similar frequency and amplitude.
Oscillations in neighboring pairs of WT neurons were strongly synchronized, whereas the oscillations of KO pairs
were uncorrelated. Spontaneous oscillations in KO neurons were not blocked by tetrodotoxin. Spontaneously oscillating
neurons of both WT and KO mice generated occasional action potentials in phase with their membrane rhythms, but
only the action potentials of WT neuron pairs were synchronous. Harmaline, a beta-carboline derivative thought
to induce tremor by facilitating rhythmogenesis in the IO, was injected systemically into WT and KO mice. Harmaline-induced
tremors were robust and indistinguishable in the two genotypes, suggesting that gap junction-mediated synchrony
does not play a role in harmaline-induced tremor. We conclude that electrical coupling is not necessary for the
generation of spontaneous subthreshold oscillations in single IO neurons, but that coupling can serve to synchronize
rhythmic activity among IO neurons.
===============
Percept Mot Skills 2002 Dec;95(3 Pt 1):1013-26
The Mozart effect may only be demonstrable in nonmusicians.
Twomey A, Esgate A.
University of Westminster, London, UK.
The "Mozart effect" is the tendency to score higher on spatiotemporal IQ subscales following exposure
to complex music such as Mozart's Sonata K.448. This phenomenon was investigated in 20 musicians and 20 nonmusicians.
The trion model predicts increased synchrony between musical and spatiotemporal centres in the right cerebral hemisphere.
Since increased left-hemispheric involvement in music processing occurs as a result of music training, predictions
deriving from the possibility of increased synchrony with left-hemispheric areas in musicians were tested. These
included improved performance on language as well as spatiotemporal tasks. Spatiotemporal, synonym generation,
and rhyming word generation tasks were employed as was the Mozart Sonata K.448. A Mozart effect was demonstrated
on the spatiotemporal task, and the facilitatory effect of exposure to Mozart was greater for the nonmusician group.
This finding adds to the robustness of the Mozart effect since novel tasks were used. No Mozart effect was found
for either group on the verbal tasks, although the musicians scored higher on rhyming word generation. This new
finding adds to the number of nonmusical tasks apparently showing long-term benefits from music training. However,
no systematic link was found between performance on any task and number of years spent in music training. The failure
to induce a Mozart effect in the musician group on verbal tasks, as well as that group's limited facilitation on
spatiotemporal tasks, may be associated with either a ceiling effect due to the long-term effects of music training
or from methodological factors. Both possibilities are discussed.
(IDM FOCUS - learnt (known) vs new (unknown) patterns in hemisphere biases)
===============
Brain Res Brain Res Rev 2003 Jan;41(1):57-78
Synchronous gamma activity: a review and contribution to an integrative neuroscience model of schizophrenia.
Lee KH, Williams LM, Breakspear M, Gordon E.
Cognitive Neuroscience Unit, Department of Psychology, University of Sydney, and The Brain Dynamics Centre, Westmead
Hospital, 2145, Sydney, NSW, Australia.
Synchronous high frequency (Gamma band) activity has been proposed as a candidate mechanism for the integration
or 'binding' of distributed brain activities. Since the first descriptions of schizophrenia, attempts to characterize
this disorder have focused on disturbances in such integrative processing. Here, we review both micro- and macroscopic
neuroscience research into Gamma synchrony, and its application to understanding schizophrenia. The review encompasses
evidence from both animal and human studies for the functional significance of Gamma activity, the association
between Gamma dysfunction and information processing disturbances, and the relevance of specific Gamma dysfunctions
to the integration and extension of previous disconnection models of schizophrenia. Attention is given to the relationship
between Gamma activity and the heterogeneous symptoms of schizophrenia. Existing studies show that measures of
Gamma activity have the potential to explain far more of the variance in schizophrenia performance than previous
neurophysiological measures. It is concluded that measures of Gamma synchrony offer a valuable window into the
core integrative disturbance in schizophrenia cognition.
(IDM FOCUS - gamma functions like a system clock, irregular timing leads to anomolies in encoding/decoding)
===============
Clin Neurophysiol 2002 Oct;113(10):1640-6
Is 'gamma' (40 Hz) synchronous activity disturbed in patients with traumatic brain injury?
Slewa-Younan S, Green AM, Baguley IJ, Felmingham KL, Haig AR, Gordon E.
Brain Injury Rehabilitation Service, Westmead Hospital, PO Box 533, Wentworthville, NSW, 2145, Australia. shameran@biru.wsahs.nsw.gov.au
OBJECTIVES: The objective of this work is to determine whether Gamma (40 Hz) synchronous activity has disturbed
patients with severe traumatic brain injury (TBI).METHODS: Using a conventional auditory oddball paradigm, the
extent of Gamma synchrony across multiple scalp sites in specific frequency bands as a function of time was examined
in 15 patients with severe TBI and 15 age- and sex-matched controls. Averaged Gamma synchrony was analyzed using
within and between group multiple analyses of variance with region (left versus right hemisphere, anterior versus
posterior region) as the within factor.RESULTS: Compared to controls, subjects with TBI displayed significantly
delayed early Gamma latency (from -150 to 150 ms) (F((1,28))=10.28, P<0.003) across all sites in addition to
other specific regional disturbances. For late Gamma synchrony, subjects with TBI displayed delayed Gamma latency
at the left hemisphere (from 200 to 450 ms) (F((1,28))=8.71, P<0.006) and posterior region (F((1,28))=9.18,
P<0.006) in comparison to controls.CONCLUSIONS: Impaired integration of spatially distributed brain activity
('40 Hz' electroencephalogram rhythms) may be an important marker of deficits of cortical network binding postulated
to be abnormal in people who have survived TBI.
===============
Naturwissenschaften 2002 Jul;89(7):316-8
Inter-cellular spike coincidences in visual detection tasks.
Bauer R, Heinze S.
FB Physik/Neurophysik, Philipps-Universitat, Marburg, Germany. roman.bauer@physik.uni-marburg.de
Synchronized spike activity is discussed as a possible representational code for object integration and as a neuronal
basis of attention, perception and awareness. As a byproduct of experiments in which monkeys were trained to detect
simple figures composed of single Gabor patches in a noisy background of similar elements, we found in special
cases increased spike synchrony above chance level specifically related to figure detection. The long latency of
this effect is difficult to interpret. It may be a sign of the cognitive state of an animal when it perceives the
figure.
==============
: J Neurosci 2002 Jul 1;22(13):5694-704
Sleep states differentiate single neuron activity recorded from human epileptic hippocampus, entorhinal cortex,
and subiculum.
Staba RJ, Wilson CL, Bragin A, Fried I, Engel J Jr.
Department of Neurobiology, David Greffen School of Medicine at University of California Los Angeles, Los Angeles,
California 90095, USA.
Animal models of epilepsy have shown that synchronous burst firing is associated with epileptogenesis, yet the
evidence from human studies linking neuronal synchrony and burst firing to epileptogenesis remains equivocal. Sleep-wake
states have been shown to differentially modulate the generation of epileptiform EEG spikes between brain regions
of greater and lesser seizure-generating potential, providing information that helps to identify the primary epileptogenic
region. Using these state-dependent mechanisms to assist us in identifying neuronal correlates of human epilepsy,
we recorded interictal neuronal activity from mesial temporal lobe (MTL) areas in epileptic patients implanted
with depth electrodes required for medical diagnosis during polysomnographically defined sleep-wake states. Results
show that single neurons recorded ipsilateral to seizure-initiating MTL ("epileptic") areas had significantly
higher firing rates (p = 0.01) and burst propensity (p = 0.01) and greater synchrony of discharges (p = 0.003)
compared with neurons recorded from contralateral non-seizure-generating MTL ("non-epileptic") areas.
In particular, during episodes of slow wave sleep (SWS) and rapid eye movement (REM) sleep, epileptic hippocampal
neurons had significantly higher burst rates compared with non-epileptic hippocampal neurons (both p = 0.01). In
contrast, during episodes of wakefulness (Aw), no difference in burst firing between epileptic and non-epileptic
hippocampal neurons was observed. Furthermore, synchronous firing was significantly higher between epileptic MTL
neurons compared with non-epileptic MTL neurons during SWS (p = 0.04) and REM sleep (p = 0.02), but no difference
in neuronal synchrony was found between epileptic and non-epileptic neurons during Aw. These results provide evidence
that sleep states differentially modulate abnormal epileptogenic neuronal discharge properties within human MTL
and confirm that neuronal burst firing and enhanced neuronal synchrony observed in experimental animal models of
epilepsy characterizes human epilepsy as well.
=============
J Neurosci 2002 Jun 1;22(11):4639-53
Enhanced synchrony among primary motor cortex neurons in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine primate
model of Parkinson's disease.
Goldberg JA, Boraud T, Maraton S, Haber SN, Vaadia E, Bergman H.
Department of Physiology, The Hebrew University-Hadassah Medical School, the Interdisciplinary Center for Neural
Computation, The Hebrew University, Jerusalem 91120, Israel. joshg@md.huji.ac.il
Primary motor cortex (MI) neurons discharge vigorously during voluntary movement. A cardinal symptom of Parkinson's
disease (PD) is poverty of movement (akinesia). Current models of PD thus hypothesize that increased inhibitory
pallidal output reduces firing rates in frontal cortex, including MI, resulting in akinesia and muscle rigidity.
We recorded the simultaneous spontaneous discharge of several neurons in the arm-related area of MI of two monkeys
and in the globus pallidus (GP) of one of the two. Accelerometers were fastened to the forelimbs to detect movement,
and surface electromyograms were recorded from the contralateral arm of one monkey. The recordings were conducted
before and after systemic treatment with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), rendering the animals
severely akinetic and rigid with little or no tremor. The mean spontaneous MI rates during periods of immobility
(four to five spikes/sec) did not change after MPTP; however, in this parkinsonian state, MI neurons discharged
in long bursts (sometimes >2 sec long). These bursts were synchronized across many cells but failed to elicit
detectable movement, indicating that even robust synchronous MI discharge need not result in movement. These synchronized
population bursts were absent from the GP and were on a larger timescale than oscillatory synchrony found in the
GP of tremulous MPTP primates, suggesting that MI parkinsonian synchrony arises independently of basal ganglia
dynamics. After MPTP, MI neurons responded more vigorously and with less specificity to passive limb movement.
Abnormal MI firing patterns and synchronization, rather than reduced firing rates, may underlie PD akinesia and
persistent muscle rigidity.
==============
Ann N Y Acad Sci 2002 Dec;978:164-74
Temporal organization of activity in the cerebellar cortex: a manifesto for synchrony.
Isope P, Dieudonne S, Barbour B.
Laboratoire de Neurobiologie (CNRS UMR 8544), Ecole Normale Superieure, 75230 Paris Cedex 05, France.
The issues of temporal coding and the temporal organization of activity have aroused a great deal of interest in
sensory systems, cortex, thalamus, and hippocampus. Strangely, despite the important timing roles attributed to
the cerebellum, little consideration has been given to the organization of activity within the cerebellar circuitry.
In fact, there is evidence of a remarkable temporal patterning of activity in even the earliest cerebellar recordings.
The evidence for the existence of high-frequency oscillations in the cerebellar cortex is reviewed and possible
mechanisms are discussed; one involves the synchrony of parallel fiber inputs to Purkinje cells. It is shown how
synchronous and oscillatory activity can enable extremely precise timing and also how they can maximize the information
storage capacity of the cerebellar cortex.
==============
AJNR Am J Neuroradiol 2003 Feb;24(2):208-12
Role of the corpus callosum in functional connectivity.
Quigley M, Cordes D, Turski P, Moritz C, Haughton V, Seth R, Meyerand ME.
Department of Medical Physics, University of Wisconsin-Madison, 1300 University Avenue, 1530 MSC, Madison, WI 53706,
USA.
BACKGROUND AND PURPOSE: Regional cerebral blood flow fluctuates synchronously in corresponding brain regions between
the hemispheres. This synchrony implies neuronal connections between brain regions. The synchrony of blood flow
changes is defined operationally as functional connectivity. Our purpose was to measure functional connectivity
in patients with corpus callosal agenesis, in whom the interhemispheric connectivity is hypothetically diminished.
METHODS: In three patients with agenesis of the corpus callosum, functional MR imaging was performed while patients
performed text-listening and finger-tapping tasks. Functional images were also acquired while the patients performed
no specific task (resting state). Regions of activation temporally correlated with the performance of the tasks
were identified by cross-correlating the task data with a reference function. Voxel clusters (seed voxels) that
corresponded to regions of activation in the task-activation data set were selected in the resting data set. All
the voxels in the resting 3D data set that had a correlation coefficient exceeding 0.4 were identified. The number
of these voxels in the ipsilateral and contralateral hemispheres was tabulated. RESULTS: In all patients, technically
adequate functional MR and functional connectivity MR maps were obtained. For both tasks, activation was found
in both hemispheres. For all of the seed voxels, significantly more functionally connected voxels were found in
the ipsilateral hemisphere than in the contralateral hemisphere. For most seed voxels, no functionally connected
voxels were found in the contralateral hemisphere. CONCLUSION: Interhemispheric functional connectivity in the
motor and auditory cortices is diminished in patients with agenesis of the corpus callosum compared with that of
healthy subjects.
==============
Life Sci Space Res 1977;15:233-7
The effect of low light intensity on the maintenance of circadian synchrony in human subjects.
Winget CM, Lyman J, Beljan JR.
Biomedical Research Division, NASA, Ames Research Center, Moffett Field, Calif, USA.
The light-intensity threshold for humans is not known. In past space flights owing to power restrictions, light
intensities have been minimal and reported to be as low as 15 ft. c. This study was conducted to determine whether
the light (L)/dark (D) environment of 16L : 8D at the relatively low light intensity of 15 ft. c. was adequate
for the maintenance of circadian synchrony in human subjects. Six healthy male subjects aged 20-23 years were exposed
for 21 days to a 16L : 8D photoperiod. During the first 7 days the light intensity was 100 ft. c.; it was reduced
to 15 ft. c. during the next 7 days and increased again to 100 ft. c. during the last 7 days of the study. Rectal
temperature (RT) and heart rate (HR) were recorded continuously throughout the 21 days of the study. In the 100
ft.c. 16L : 8D the RT and HR rhythms remained stable and circadian throughout. When the light intensity was decreased
to 15 ft.c. the periodicity of the HR rhythm was significantly decreased and this rhythm showed marked instability.
In contrast the period of the RT rhythm did not change but a consistent phase delay occurred due to a delay in
the lights-on associated rise in RT. These divergent effects on these two rhythms in internal desynchronization
and performance decrement during the 15 ft.c. exposure. The data emphasize the need for establishing accurately
the minimal lighting requirements for the maintenance of circadian rhythms of humans in confined environments.
===============
Neural Comput 2003 Mar;15(3):509-38
Synchronization in networks of excitatory and inhibitory neurons with sparse, random connectivity.
Borgers C, Kopell N.
Department of Mathematics, Tufts University, Medford, MA 02155, U.S.A. chritopher.borgers@tufts.edu
In model networks of E-cells and I-cells (excitatory and inhibitory neurons, respectively), synchronous rhythmic
spiking often comes about from the interplay between the two cell groups: the E-cells synchronize the I-cells and
vice versa. Under ideal conditions-homogeneity in relevant network parameters and all-to-all connectivity, for
instance-this mechanism can yield perfect synchronization. We find that approximate, imperfect synchronization
is possible even with very sparse, random connectivity. The crucial quantity is the expected number of inputs per
cell. As long as it is large enough (more precisely, as long as the variance of the total number of synaptic inputs
per cell is small enough), tight synchronization is possible. The desynchronizing effect of random connectivity
can be reduced by strengthening the E --> I synapses. More surprising, it cannot be reduced by strengthening
the I --> E synapses. However, the decay time constant of inhibition plays an important role. Faster decay yields
tighter synchrony. In particular, in models in which the inhibitory synapses are assumed to be instantaneous, the
effects of sparse, random connectivity cannot be seen.
==============
Philos Trans R Soc Lond B Biol Sci 2002 Dec 29;357(1428):1659-73
Thalamic circuitry and thalamocortical synchrony.
Jones EG.
Center for Neuroscience, University of California, Davis, Davis, CA 95616, USA. ejones@ucdavis.edu
The corticothalamic system has an important role in synchronizing the activities of thalamic and cortical neurons.
Numerically, its synapses dominate the inputs to relay cells and to the gamma-amino butyric acid (GABA)ergic cells
of the reticular nucleus (RTN). The capacity of relay neurons to operate in different voltage-dependent functional
modes determines that the inputs from the cortex have the capacity directly to excite the relay cells, or indirectly
to inhibit them via the RTN, serving to synchronize high- or low-frequency oscillatory activity respectively in
the thalamocorticothalamic network. Differences in the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid
(AMPA) subunit composition of receptors at synapses formed by branches of the same corticothalamic axon in the
RTN and dorsal thalamus are an important element in the capacity of the cortex to synchronize low-frequency oscillations
in the network. Interactions of focused corticothalamic axons arising from layer VI cortical cells and diffuse
corticothalamic axons arising from layer V cortical cells, with the specifically projecting core relay cells and
diffusely projecting matrix cells of the dorsal thalamus, form a substrate for synchronization of widespread populations
of cortical and thalamic cells during high-frequency oscillations that underlie discrete conscious events.
===============
Nat Neurosci 2003 Jun;6(6):593-9
Synchrony-dependent propagation of firing rate in iteratively constructed networks in vitro.
Reyes AD.
Center for Neural Science, New York University, 4 Washington Place, New York, New York 10003, USA. reyes@cns.nyu.edu
The precise role of synchronous neuronal firing in signal encoding remains unclear. To examine what kinds of signals
can be carried by synchrony, I reproduced a multilayer feedforward network of neurons in an in vitro slice preparation
of rat cortex using an iterative procedure. When constant and time-varying frequency signals were delivered to
the network, the firing of neurons in successive layers became progressively more synchronous. Notably, synchrony
in the in vitro network developed even with uncorrelated input, persisted under a wide range of physiological conditions
and was crucial for the stable propagation of rate signals. The firing rate was represented by a classical rate
code in the initial layers, but switched to a synchrony-based code in the deeper layers.
===============
Neuron 2003 Apr 10;38(1):115-25
Synchrony between Neurons with Similar Muscle Fields in Monkey Motor Cortex.
Jackson A, Gee VJ, Baker SN, Lemon RN.
Sobell Department of Motor Neuroscience and Movement Disorders, Institute of Neurology, UCL, WC1N 3BG, London,
United Kingdom
Synchronous firing of motor cortex cells exhibiting postspike facilitation (PSF) or suppression (PSS) of hand muscle
EMG was examined to investigate the relationship between synchrony and output connectivity. Recordings were made
in macaque monkeys performing a precision grip task. Synchronization was assessed with cross-correlation histograms
of the activity from 144 pairs of simultaneously recorded neurons, while spike-triggered averages of EMG defined
the muscle field for each cell. Cell pairs with similar muscle fields showed greater synchronization than pairs
with nonoverlapping fields. Furthermore, cells with opposing effects in the same muscles exhibited negative synchronization.
We conclude that synchrony in motor cortex engages networks of neurons directly controlling the same muscle set,
while inhibitory connections exist between neuronal populations with opposing output effects.
===============
Neuropsychopharmacology 2003 May;28(5):857-64
Norepinephrine but not Serotonin Reuptake Inhibitors Enhance Theta and Gamma Activity of the Septo-Hippocampal
System.
Hajos M, Hoffmann WE, Robinson DD, Yu JH, Hajos-Korcsok E.
1Neurobiology, Pharmacia Corporation, Kalamazoo, MI, USA.
Current neurobiological concepts attribute a central role of the hippocampal formation in cognitive and affective
processes. Recent studies indicate that the hippocampus is affected in human depression, and antidepressant drugs
induce hippocampal adaptive changes that are thought to be associated with their therapeutic action. In the present
study, we investigated the action of various antidepressant drugs on the activity of the septo-hippocampal system,
its oscillatory activity in particular. The acute effects of the norepinephrine (NE) reuptake inhibitors reboxetine
and desipramine, and the selective serotonin reuptake inhibitor fluvoxamine were evaluated. Extracellular single-unit
recordings were performed from the medial septum/diagonal band of Broca (MS/DBv), with simultaneous hippocampal
EEG recordings of anesthetized rats. Systemic administration of reboxetine synchronized hippocampal EEG, resulting
in a significant increase in power at theta frequency, and an increase in frequency and power of gamma-wave activity.
Parallel to EEG synchrony, reboxetine induced or enhanced theta oscillation of MS/DBv neurons. Oscillatory frequencies
of MS/DBv neurons were identical, and phase locked to the corresponding hippocamapal theta frequencies. Under the
same experimental conditions, reboxetine induced a two-fold increase in extracellular NE (but not serotonin) levels
in the hippocampus as revealed by microdialysis. Desipramine, but not the serotonin reuptake inhibitor fluvoxamine,
evoked responses similar to those of reboxetine regarding septo-hippocampal theta activity. The present findings
indicate that even though both NE and serotonin reuptake inhibitors are clinically effective antidepressant drugs,
their action on the septo-hippocampal oscillatory behavior is different. It is presumed that selective NE reuptake
inhibitors could modulate various cognitive processes associated with hippocampal oscillatory activity.Neuropsychopharmacology
(2003) 28, 857-864,
(IDM FOCUS - issue on LINKAGE)
===============
Phys Rev Lett 2003 Feb 28;90(8):088101
Synchronization tomography: a method for three-dimensional localization of phase synchronized neuronal populations
in the human brain using magnetoencephalography.
Tass PA, Fieseler T, Dammers J, Dolan K, Morosan P, Majtanik M, Boers F, Muren A, Zilles K, Fink GR.
Institute of Medicine, Research Center Julich, 52425 Julich, Germany.
We present a noninvasive technique which allows the anatomical localization of phase synchronized neuronal populations
in the human brain with magnetoencephalography. We study phase synchronization between the reconstructed current
source density (CSD) of different brain areas as well as between the CSD and muscular activity. We asked four subjects
to tap their fingers in synchrony with a rhythmic tone, and to continue tapping at the same rate after the tone
was switched off. The phase synchronization behavior of brain areas relevant for movement coordination, inner voice,
and time estimation changes drastically when the transition to internal pacing occurs, while their averaged amplitudes
remain unchanged. Information of this kind cannot be derived with standard neuroimaging techniques like functional
magnetic resonance imaging or positron emission tomography.
(IDM fous - Subjective time experience)
==============
Cell Cycle 2003 Jan-Feb;2(1):42-5
Synchrony in human, mouse and bacterial cell cultures a comparison.
Helmstetter CE, Thornton M, Romero A, Eward LK.
Correspondence to: Charles E. Helmstetter; Department of Biological Sciences; Florida Institute of Technology;
Melbourne, Florida 32901 USA; Tel.: 321.674.8575; Fax: 321.674.7238.
Growth characteristics of synchronous human MOLT-4, human U-937 and mouse L1210 cultures produced with a new minimally-disturbing
technology were compared to each other and to synchronous Escherichia coli B/r. Based on measurements of cell concentrations
during synchronous growth, synchrony persisted in similar fashion for all cells. Cell size and DNA distributions
in the mammalian cultures also progressed synchronously and reproducibly for multiple cell cycles. The results
demonstrate that unambiguous multi-cycle synchrony, critical for verifying the absence of significant growth imbalances
induced by the synchronization procedure, is feasible with these cell lines, and possibly others.
================
J Neurophysiol 2003 Apr 17;
Features of Neuronal Synchrony in Mouse Visual Cortex.
Nase G, Singer W, Monyer H, Engel AK.
Neurophysiologie, Max-Planck-Institut fuer Hirnforschung, Frankfurt, Germany.
Synchronization of neuronal discharges has been hypothesized to play a role in defining cell assemblies representing
particular constellations of stimulus features. In many systems and species, synchronization is accompanied by
an oscillatory response modulation at frequencies in the gamma-band (>30Hz). The cellular mechanisms underlying
these phenomena of synchronization and oscillatory patterning have been studied mainly in vitro due to the difficulty
in designing a direct in vivo assay. With the prospect of utilizing conditional genetic manipulations of cortical
network components, our objective was to test whether the mouse would meet the criteria to provide a model system
for the study of gamma-band synchrony. Multi-unit and local field potential recordings were made from the primary
visual cortex of anesthetized C57BL/6J mice. Neuronal responses evoked by moving gratings, bars and random dot
patterns were analyzed with respect to neuronal synchrony and temporal patterning. Oscillations at gamma frequencies
were readily evoked with all types of stimuli used. Oscillation and synchronization strength were largest for gratings
and decreased when the noise level was increased in random-dot patterns. The center peak width of cross-correlograms
was smallest for bars and increased with noise, yielding a significant difference between coherent random dot patterns
versus patterns with >70% noise. Field potential analysis typically revealed increases of power in the gamma-band
during response periods. Our findings are compatible with a role for neuronal synchrony in mediating perceptual
binding and suggest the usefulness of the mouse model for testing hypotheses concerning both the mechanisms and
the functional role of temporal patterning.
===============
Brain Lang 2003 May;85(2):297-312
Cortical operational synchrony during audio-visual speech integration.
Fingelkurts AA, Fingelkurts AA, Krause CM, Mottonen R, Sams M.
Human Brain Research Group, Human Physiology Department, Moscow State University, 119899, Moscow, Russian Federation
Information from different sensory modalities is processed in different cortical regions. However, our daily perception
is based on the overall impression resulting from the integration of information from multiple sensory modalities.
At present it is not known how the human brain integrates information from different modalities into a unified
percept. Using a robust phenomenon known as the McGurk effect it was shown in the present study that audio-visual
synthesis takes place within a distributed and dynamic cortical networks with emergent properties. Various cortical
sites within these networks interact with each other by means of so-called operational synchrony (). The temporal
synchronization of cortical operations processing unimodal stimuli at different cortical sites reveals the importance
of the temporal features of auditory and visual stimuli for audio-visual speech integration.
===============
J Comput Neurosci 2003 May-Jun;14(3):283-309
Dynamics of spiking neurons connected by both inhibitory and electrical coupling.
Lewis TJ, Rinzel J.
Center for Neural Science and Courant Institute for Mathematical Science, New York University, 4 Washington Place,
Rm 809, NY 10003, USA. tim.lewis@nyu.edu
We study the dynamics of a pair of intrinsically oscillating leaky integrate-and-fire neurons (identical and noise-free)
connected by combinations of electrical and inhibitory coupling. We use the theory of weakly coupled oscillators
to examine how synchronization patterns are influenced by cellular properties (intrinsic frequency and the strength
of spikes) and coupling parameters (speed of synapses and coupling strengths). We find that, when inhibitory synapses
are fast and the electrotonic effect of the suprathreshold portion of the spike is large, increasing the strength
of weak electrical coupling promotes synchrony. Conversely, when inhibitory synapses are slow and the electrotonic
effect of the suprathreshold portion of the spike is small, increasing the strength of weak electrical coupling
promotes antisynchrony (see Fig. 10). Furthermore, our results indicate that, given a fixed total coupling strength,
either electrical coupling alone or inhibition alone is better at enhancing neural synchrony than a combination
of electrical and inhibitory coupling. We also show that these results extend to moderate coupling strengths.
==============
J Exp Psychol Hum Percept Perform 2003 Apr;29(2):290-309
Phase attraction in sensorimotor synchronization with auditory sequences: effects of single and periodic distractors
on synchronization accuracy.
Repp BH.
Haskins Laboratories, New Haven, Connecticut 06511-6695, USA. repp@haskins.yale.edu
Four experiments showed that both single and periodic distractor tones affected the timing of finger taps produced
in synchrony with an isochronous auditory target sequence. Single distractors had only small effects, but periodic
distractors occurring at various fixed or changing phase relationships exerted strong phase attraction. The attraction
was asymmetric, being stronger when distractors preceded target tones than when they lagged behind. A large pitch
difference between target and distractor tones (20 vs. 3 semitones) did not reduce phase attraction substantially,
although in the case of continuously changing phase relationships it did prevent complete capture of the taps by
the distractors. The results support the hypothesis that phase attraction is an automatic process that is sensitive
primarily to event onsets.
=============
Brain Lang 2003 May;85(2):211-21
Neural basis for sentence comprehension deficits in frontotemporal dementia.
Cooke A, DeVita C, Gee J, Alsop D, Detre J, Chen W, Grossman M.
Department of Neurology-2 Gibson, University of Pennsylvania Medical Center, 3400 Spruce Street, 19104-4283, Philadelphia,
PA, USA
Many patients with frontotemporal dementia (FTD) have impaired sentence comprehension. However, the pattern of
comprehension difficulty appears to vary depending on the clinical subgroup. The purpose of this study was to elucidate
the neural basis for these deficits in FTD. We studied patients with two different presentations: Three patients
with Progressive Non-Fluent Ahasia (PNFA), and five non-aphasic patients with a dysexecutive and social impairment
(EXEC). The FTD patient subgroups were compared to a cohort of 11 healthy seniors with intact sentence comprehension.
We monitored regional cerebral activity with blood oxygen level dependent (BOLD) functional magnetic resonance
imaging (fMRI) while subjects read sentences featuring both a grammatically complex object-relative center-embedded
clause and a long linkage between the head noun phrase (NP) and the gap where the NP is interpreted in the center-embedded
clause. Subjects decided whether the agent of the action is a male or a female. Healthy seniors activated both
ventral portions of inferior frontal cortex (vIFC) and dorsal portions of IFC (dIFC) in the left hemisphere, often
associated with grammatical and working memory components of these sentences, respectively. PNFA patients differed
from healthy controls since they have reduced activation of left vIFC, while EXEC patients have less recruitment
of left dIFC. We conclude that FTD subgroups have distinct patterns of sentence comprehension difficulty in part
because of selective interruptions of a large-scale neural network for sentence processing.
==============
Brain Res Cogn Brain Res 2003 Jun;17(1):56-67
Shared and dissociated cortical regions for object and letter processing.
Joseph JE, Gathers AD, Piper GA.
Department of Anatomy and Neurobiology, University of Kentucky Medical Center, 800 Rose Street, Davis-Mills Building,
Room 308, 40536-0098, Lexington, KY, USA
The present study determined the extent to which object and letter recognition recruit similar or dissociated neural
resources. Participants passively viewed and silently named line drawings of objects, single letters, and visual
noise patterns and centrally fixated an asterisk. We used whole-brain functional MRI and a very conservative approach
to hypothesis testing that distinguished among brain regions that were selectively activated by different experimental
conditions and those that were conjointly activated. The left fusiform gyrus (BA 19 & 37) and left inferior
frontal cortex BA(44/6) showed a greater degree of conjoined activation for objects and letters than selective
activation for either category, whereas left inferior parietal cortex (BA 40) and the left insula showed a strong
letter-selective response. Equal recruitment of left fusiform and inferior frontal regions by objects and letters
reflects similar demands on cognitive processing by these two categories and argues against category-specific modules
in these regions. However, cortical systems for object and letter processing are not completely shared given the
exclusive activation of left inferior parietal cortex by letters.
==============
J Neurophysiol 2003 May 15;
Synchrony levels during Evoked Seizure-Like Bursts in Mouse Neocortical Slices.
Van Drongelen W, Koch H, Marcuccilli C, Pena F, Ramirez JM.
Pediatrics, The University of Chicago, Chicago, IL, USA; Neurology, The University of Chicago, Chicago, IL, USA.
Slices (n = 45) from the somatosensory cortex of mouse (P8-13) generate spontaneous bursts of activity (0.10 +/-0.05
Hz) that were recorded extracellularly. Multi-unit action potential (AP) activity was integrated and used as an
index of population activity. In this experimental model, seizure-like activity (SLA) was evoked with bicuculline
(5-10 micro M) or N-methyl-D-aspartate (NMDA, 5 micro M). SLA was an episode with repetitive bursting at a frequency
of 0.50 +/-0.06 Hz. To evaluate whether SLA was associated with a change in synchrony, we obtained simultaneous
intracellular and extracellular recordings (n = 40) and quantified the relationship between individual cells and
the surrounding population of neurons. During the SLA there was an increase in population activity and bursting
activity was observed in neurons and areas that were previously silent. We defined synchrony as cellular activity
that is consistently locked with the population bursts. Signal averaging techniques were used to determine this
component. To quantitatively assess change in synchronous activity at SLA onset, we estimated the entropy of the
single cell spike trains and subdivided this measure into network burst related information and noise-related entropy.
The burst related information was not significantly altered at the onset of NMDA evoked SLA and slightly increased
when evoked with bicuculline. The signal-to-noise ratio determined from the entropy estimates showed a significant
decrease (instead of an expected increase) during SLA. We conclude that the increased population activity during
the SLA is due to recruitment of neurons rather than increased synchrony of each of the individual elements.
==============
International Journal of Bifurcation and Chaos, Vol. 10, No. 10 (2000) 2307-2322
CHARACTERISTICS OF THE SYNCHRONIZATION OF BRAIN ACTIVITY IMPOSED BY FINITE CONDUCTION VELOCITIES OF AXONS
WALTER J. FREEMAN
Division of Neurobiology LSA 129, Department of Molecular & Cell Biology, University of California, Berkeley
CA 94720-3200, USA
The electrical activity of neurons in brains fluctuates erratically both in terms of pulse trains of single neurons
and the dendritic currents of populations of neurons. Obviously the neurons interact with one another in the production
of intelligent behavior, so it is reasonable to expect to find evidence for varying degrees of synchronization
of their pulse trains and dendritic currents in relation to behavior. However, synaptic communication between neurons
depends on propagation of action potentials between neurons, often with appreciable distances between them, and
the transmission delays are not compatible with synchronization in any simple way. Evidence is on hand showing
that the principal form of synchrony is by establishment of a low degree of covariance among very large numbers
of otherwise autonomous neurons, which allows for rapid state transitions of neural populations between successive
chaotic basins of attraction along itinerant trajectories. The small fraction of covariant activity is extracted
by spatial integration upon axonal transmission over divergent-convergent pathways, through which a remarkable
improvement in signal-to-noise ratio is achieved. The raw traces of local activity show little evidence for synchrony,
other than zero-lag correlation, which appears to be largely a statistical artifact. Brains rely less on tight
phase-locking of small numbers of periodically firing neurons and more on low degrees of cooperativity achieved
by order parameters influencing very large numbers of neurons. Brains appear to be indifferent to and undisturbed
by widely varying time and phase relations between individual neurons and even large semi-autonomous areas of cortex
comprising their mesoscopic neural masses.
(IDM - Issues of synchrony in brain, con as compared to pro)
=============
Exp Brain Res 2003 May 9;
Ia Afferent input alters the recruitment thresholds and firing rates of single human motor units.
Grande G, Cafarelli E.
Kinesiology and Health Science, Faculty of Pure and Applied Science, York University, Toronto, Canada.
Vibration of the patellar tendon recruits motor units in the knee extensors via excitation of muscle spindles and
subsequent Ia afferent input to the alpha-motoneuron pool. Our first purpose was to determine if the recruitment
threshold and firing rate of the same motor unit differed when recruited involuntarily via reflex or voluntarily
via descending spinal pathways. Although Ia input is excitatory to the alpha-motoneuron pool, it has also been
shown paradoxically to inhibit itself. Our second purpose was to determine if vibration of the patellar tendon
during a voluntary knee extension causes a change in the firing rate of already recruited motor units. In the first
protocol, 10 subjects voluntarily reproduced the same isometric force profile of the knee extensors that was elicited
by vibration of the patellar tendon. Single motor unit recordings from the vastus lateralis (VL) were obtained
with tungsten microelectrodes and unitary behaviour was examined during both reflex and voluntary knee extensions.
Recordings from 135 single motor units showed that both recruitment thresholds and firing rates were lower during
reflex contractions. In the second protocol, 7 subjects maintained a voluntary knee extension at 30 N for approximately
40-45 s. Three bursts of patellar tendon vibration were superimposed at regular intervals throughout the contraction
and changes in the firing rate of already recruited motor units were examined. A total of 35 motor units were recorded
and each burst of superimposed vibration caused a momentary reduction in the firing rates and recruitment of additional
units. Our data provide evidence that Ia input modulates the recruitment thresholds and firing rates of motor units
providing more flexibility within the neuromuscular system to grade force at low levels of force production.
==============
Exp Brain Res 2003 Jan;148(2):238-46
Processing of temporal information and the basal ganglia: new evidence from fMRI.
Nenadic I, Gaser C, Volz HP, Rammsayer T, Hager F, Sauer H.
Department of Psychiatry, Friedrich-Schiller-University of Jena, Philosophenweg 3, 07740 Jena, Germany, igor.nenadic@uni-jena.de
Temporal information processing is a fundamental brain function, which might include central timekeeping mechanisms
independent of sensory modality. Psychopharmacological and patient studies suggest a crucial role of the basal
ganglia in time estimation. In this study, functional magnetic resonance imaging (fMRI) was applied in 15 healthy
right-handed male subjects performing an auditory time estimation task (duration discrimination of tone pairs in
the range of 1,000-1,400 ms) and frequency discriminations (tone pairs differing in pitch, around 1,000 Hz) as
an active control task. Task difficulty was constantly modulated by an adaptive algorithm (weighted up-down method)
reacting on individual performance. Time estimation (vs rest condition) elicited a distinct pattern of cerebral
activity, including the right medial and both left and right dorsolateral prefrontal cortices (DLPFC), thalamus,
basal ganglia (caudate nucleus and putamen), left anterior cingulate cortex, and superior temporal auditory areas.
Most activations showed lateralisation to the right hemisphere and were similar in the frequency discrimination
task. Comparing time and frequency tasks, we isolated activation in the right putamen restricted to time estimation
only. This result supports the notion of central processing of temporal information associated with basal ganglia
activity. Temporal information processing in the brain might thus be a distributed process of interaction between
modality-dependent sensory cortical function, the putamen (with a timing-specific function), and additional prefrontal
cortical systems related to attention and memory. Further investigations are needed to delineate the differential
contributions of the striatum and other areas to timing.
========================================
J Neurophysiol 2003 Jan;89(1):460-71
Modulation of cortical activity during different imitative behaviors.
Koski L, Iacoboni M, Dubeau MC, Woods RP, Mazziotta JC.
Ahmanson-Lovelace Brain Mapping Center, Neuropsychiatric Institute, UCLA School of Medicine, Los Angeles, California
90095.
Imitation is a basic form of motor learning during development. We have a preference to imitate the actions of
others as if looking in a mirror (specular imitation: i.e., when the actor moves the left hand, the imitator moves
the right hand) rather than with the anatomically congruent hand (anatomic imitation: i.e., actor and imitator
both moving the right hand). We hypothesized that this preference reflects changes in activity in previously described
frontoparietal cortical areas involved in directly matching observed and executed actions (mirror neuron areas).
We used functional magnetic resonance imaging to study brain activity in normal volunteers imitating left and right
hand movements with their right hand. Bilateral inferior frontal and right posterior parietal cortex were more
active during specular imitation compared with anatomic imitation and control motor tasks. Furthermore this same
pattern of activity was also observed in the rostral part of the supplementary motor area (SMA-proper) of the right
hemisphere. These findings suggest that the degree of involvement of frontoparietal mirror areas in imitation depends
on the nature of the imitative behavior, ruling out a linguistic mediation of these areas in imitation. Moreover,
activity in the SMA appears to be tightly coupled to frontoparietal mirror areas when subjects copy the actions
of others.
===========================
Proc Natl Acad Sci U S A 2003 Feb 4;100(3):1370-4
Contrasting roles of axonal (pyramidal cell) and dendritic (interneuron) electrical coupling in the generation
of neuronal network oscillations.
Traub RD, Pais I, Bibbig A, LeBeau FE, Buhl EH, Hormuzdi SG, Monyer H, Whittington MA.
Department of Physiology and Pharmacology, State University of New York Downstate Medical Center, 450 Clarkson
Avenue, Box 31, Brooklyn, NY 11203, USA. roger.traub@downstate.edu
Electrical coupling between pyramidal cell axons, and between interneuron dendrites, have both been described in
the hippocampus. What are the functional roles of the two types of coupling? Interneuron gap junctions enhance
synchrony of gamma oscillations (25-70 Hz) in isolated interneuron networks and also in networks containing both
interneurons and principal cells, as shown in mice with a knockout of the neuronal (primarily interneuronal) connexin36.
We have recently shown that pharmacological gap junction blockade abolishes kainate-induced gamma oscillations
in connexin36 knockout mice; without such gap junction blockade, gamma oscillations do occur in the knockout mice,
albeit at reduced power compared with wild-type mice. As interneuronal dendritic electrical coupling is almost
absent in the knockout mice, these pharmacological data indicate a role of axonal electrical coupling in generating
the gamma oscillations. We construct a network model of an experimental gamma oscillation, known to be regulated
by both types of electrical coupling. In our model, axonal electrical coupling is required for the gamma oscillation
to occur at all; interneuron dendritic gap junctions exert a modulatory effect
===========================
Nature 2003 Jan 23;421(6921):366-70
Neuronal synchrony does not correlate with motion coherence in cortical area MT.
Thiele A, Stoner G.
Salk Institute for Biological Studies, La Jolla, California 92037, USA.
Natural visual scenes are cluttered with multiple objects whose individual features must somehow be selectively
linked (or 'bound') if perception is to coincide with reality. Recent neurophysiological evidence supports a 'binding-by-synchrony'
hypothesis: neurons excited by features of the same object fire synchronously, while neurons excited by features
of different objects do not. Moving plaid patterns offer a straightforward means to test this idea. By appropriate
manipulations of apparent transparency, the component gratings of a plaid pattern can be seen as parts of a single
coherently moving surface or as two non-coherently moving surfaces. We examined directional tuning and synchrony
of area-MT neurons in awake, fixating primates in response to perceptually coherent and non-coherent plaid patterns.
Here we show that directional tuning correlated highly with perceptual coherence, which is consistent with an earlier
study. Although we found stimulus-dependent synchrony, coherent plaids elicited significantly less synchrony than
did non-coherent plaids. Our data therefore do not support the binding-by-synchrony hypothesis as applied to this
class of motion stimuli in area MT.
==========================
J Acoust Soc Am 2003 Jan;113(1):462-7
Effect of amplitude modulation coherence for masked speech signals filtered into narrow bands.
Buss E, Wall JW 3rd, Grose JH.
Department of Otolaryngology/Head and Neck Surgery, University of North Carolina School of Medicine, Chapel Hill,
North Carolina 27599, USA. ebuss@med.unc.edu
Introduction of masker amplitude modulation (AM) can improve signal detection in a number of paradigms. In some
cases this advantage depends on the coherence of modulation across a relatively wide frequency range. In the experiments
described below, observers were asked to identify masked spondee words produced by a single male talker. The target
spondees and masking noise were filtered into nine narrow bands, and the coherence of AM of either the speech signal
or noise masker was manipulated. Inherent modulation of the masker bands was manipulated via assignment of real
and imaginary values to the associated components of each band in the frequency domain, and AM of speech bands
was achieved via multiplication with envelopes extracted from these maskers. Responses were based on two alternatives,
four alternatives, or open response sets. The effect of masker AM coherence was highly dependent upon the size
of the response set: coherent AM was associated with better thresholds in a two-alternative response set, but poorer
thresholds in an open response set. Results with AM speech did not depend critically upon the across-frequency
temporal synchrony of AM imposed on the speech material.
===============================
Neuropsychol Rev 2002 Dec;12(4):233-51
Hemisphere specialization as an aid in early infancy.
Burnand G.
burn@globalnet.co.uk
In order that different directions of attention can be organized, they have to be labeled and assessed. A statement
of a general problem can be regarded as a label for a general direction of attention. Hope about it, as the perceived
probability of sufficient success, on the basis of work done, can be regarded as an assessment. It can be argued
that a young infant meets an impasse arising from the work on 2 incompatible general problems, (1) that of raising
hope of certainty about the environment (linked to the arousal system because repeated stimulation has less effect),
and (2) that of raising hope of producing effects (linked to the activation system because here some effect must
be produced before activity can cease). A certainty-right hypothesis, that the right hemisphere deals with the
certainty problem and the left deals with the producing-effects problem, and hence keeps work on the two problems
apart in early infancy while the corpus callosum is undeveloped, and that a matching specialization continues in
later life, is supported.
============================
Hermaphrodite finch hints genes mould brain
Sex chromosomes split personality in bird possessing testis and ovary.
25 March 2003
JOHN WHITFIELD
The half-half finch: male on one side, female on the other
A half-male, half-female bird has added to evidence that genes - not only hormones - underlie the differences between
male and female brains.
The cells on the right half of the bird's body contained male sex chromosomes, those on the left, female. The zebra
finch had one testis and one ovary; its plumage was bright on its right half, and drab on its left.
It also had a split personality. When ornithologist John Wingfield and his colleagues looked at the bird's brain,
they saw that it, too, was divided into male and female sides.
The areas that control singing were bigger on the male side. Male finches court mates with loud and complex songs;
females are quieter.
It had been thought that sex differences in the brain were caused by hormones released by the gonads, and were
not due to the nerve cells themselves. But both halves of the brain would have received the same chemical signals
from the gonads, showing that the different genetic make-up of the brain's two halves must also have had an effect.
The divided bird sang a male's song, and mated a female finch that then laid infertile eggs. The researchers put
down the bird when it was almost two years old.
The bizarre zebra finch (Taeniopygia guttata) was born in a lab at Rockefeller University, New York, possibly from
a cell containing both male and female chromosomes that was fertilized by two sperm.
Wingfield, who works at the University of Washington, Seattle, was baffled when he first saw the animal - it seemed
to change sex before his eyes as it turned. "It was split straight down the middle," he says.
References
Agate, R. J. et al. Neural, not gonadal, origin of brain sex differences in a gynandromorphic finch. Proceedings
of the National Academy of Sciences, (2003).
===========================
Neuron 2002 Dec 19;36(6):1221-31
The role of medial temporal lobe structures in implicit learning: an event-related FMRI study.
Rose M, Haider H, Weiller C, Buchel C.
Cognitive Neuroscience Laboratory, Department of Neurology, University of Hamburg Medical School, D-20246, Hamburg,
Germany. rose@uke.uni-hamburg.de
The medial temporal lobe (MTL) has been associated with declarative learning of flexible relational rules and the
basal ganglia with implicit learning of stimulus-response mappings. It remains an open question of whether MTL
or basal ganglia are involved when learning flexible relational contingencies without awareness. We studied learning
of an explicit stimulus-response association with fMRI. Embedded in this explicit task was a hidden structure that
was learnt implicitly. Implicit learning of the sequential regularities of the "hidden rule" activated
the ventral perirhinal cortex, within the MTL, whereas learning the fixed stimulus-response associations activated
the basal ganglia, indicating that the function of the MTL and the basal ganglia depends on the learned material
and not necessarily on the participants' awareness.
===============================
Neuroreport 2002 Dec 20;13(18):2475-2481
Alteration of functional neuroanatomy of simple object memory in medial temporal lobe epilepsy patients.
Kang E, Nam H, Lee DS, Lee SK, Lee K, Park SH, Lee JS, Chung JK, Lee MC.
Institute of Radiation Medicine, Seoul National University Medical Research Center Departments of Nuclear Medicine.
Using H O PET, we examined the neuroanatomy associated with a simple form of episodic memory in patients with right
or left medial temporal lobe epilepsy and normal healthy controls. When line drawings of common objects were memorized
and tested after a 30 min delay, no behavioral difference was found between the patient groups and the controls.
However, the patients with epilepsy showed greater cortical activations than the control group on the side ipsilateral
to the epileptic focus. rCBF in the anterior thalamic region was enhanced in patients relative to the control group.
The results showed that long-term dysfunction of the medial temporal lobe might reinforce alternative memory pathways
and recruit a distributed cortical network ipsilateral to their epilepsy focus.(2)
======================
Neuron 2003 Jan 9;37(1):171-80
Recognition memory and the human hippocampus.
Manns JR, Hopkins RO, Reed JM, Kitchener EG, Squire LR.
University of California, San Diego, 92093, La Jolla, CA, USA
The capacity for declarative memory depends on the hippocampal region and adjacent cortex within the medial temporal
lobe. One of the most widely studied examples of declarative memory is the capacity to recognize recently encountered
material as familiar, but uncertainty remains about whether intact recognition memory depends on the hippocampal
region itself and, if so, what the nature of the hippocampal contribution might be. Seven patients with bilateral
damage thought to be limited primarily to the hippocampal region were impaired on three standard tests of recognition
memory. In addition, the patients were impaired to a similar extent at Remembering and Knowing, measures of the
two processes thought to support recognition performance: the ability to remember the learning episode (episodic
recollection) and the capacity for judging items as familiar (familiarity).
=========================
Rev Neurosci 2002;13(4):299-312
The interaction of rhinal cortex and hippocampus in human declarative memory formation.
Fell J, Klaver P, Elger CE, Fernandez G.
Department of Epileptology, University of Bonn, Bonn, Germany. juergen.fell@ukb.uni-bonn.de
Human declarative memory formation crucially depends on processes within the medial temporal lobe (MTL). These
processes can be monitored in real-time by recordings from depth electrodes implanted in the MTL of patients with
epilepsy who undergo presurgical evaluation. In our studies, patients performed a word memorization task during
depth EEG recording. Afterwards, the difference between event-related potentials (ERPs) corresponding to subsequently
remembered versus forgotten words was analyzed. These kind of studies revealed that successful memory encoding
is characterized by an early process generated by the rhinal cortex within 300 ms following stimulus onset. This
rhinal process precedes a hippocampal process, which starts about 200 ms later. Further investigation revealed
that the rhinal process seems to be a correlate of semantic preprocessing which supports memory formation, whereas
the hippocampal process appears to be a correlate of an exclusively mnemonic operation. These studies yielded only
indirect evidence for an interaction of rhinal cortex and hippocampus. Direct evidence for a memory related cooperation
between both structures, however, has been found in a study analyzing so called gamma activity, EEG oscillations
of around 40 Hz. This investigation showed that successful as opposed to unsuccessful memory formation is accompanied
by an initial enhancement of rhinal-hippocampal phase synchronization, which is followed by a later desynchronization.
Present knowledge about the function of phase synchronized gamma activity suggests that this phase coupling and
decoupling initiates and later terminates communication between the two MTL structures. Phase synchronized rhinal-hippocampal
gamma activity may, moreover, accomplish Hebbian synaptic modifications and thus provide an initial step of declarative
memory formation on the synaptic level.
============================
Science 2003 Jan 24;299(5606):577-80
Dynamics of the hippocampus during encoding and retrieval of face-name pairs.
Zeineh MM, Engel SA, Thompson PM, Bookheimer SY.
Ahmanson-Lovelace Brain Mapping Center, UCLA School of Medicine, 660 Charles Young Drive South, Los Angeles, CA
90095-7085, USA.
The medial temporal lobe (MTL) is critical in forming new memories, but how subregions within the MTL carry out
encoding and retrieval processes in humans is unknown. Using new high-resolution functional magnetic resonance
imaging (fMRI) acquisition and analysis methods, we identified mnemonic properties of different subregions within
the hippocampal circuitry as human subjects learned to associate names with faces. The cornu ammonis (CA) fields
2 and 3 and the dentate gyrus were active relative to baseline only during encoding, and this activity decreased
as associations were learned. Activity in the subiculum showed the same temporal decline, but primarily during
retrieval. Our results demonstrate that subdivisions within the hippocampus make distinct contributions to new
memory formation.
==========================
J Neurophysiol 2002 Sep;88(3):1433-50
Sound repetition rate in the human auditory pathway: representations in the waveshape and amplitude of fMRI activation.
Harms MP, Melcher JR.
Eaton-Peabody Laboratory, Massachusetts Eye and Ear Infirmary, Boston 02114, USA. mharms@epl.meei.harvard.edu
Sound repetition rate plays an important role in stream segregation, temporal pattern recognition, and the perception
of successive sounds as either distinct or fused. This study was aimed at elucidating the neural coding of repetition
rate and its perceptual correlates. We investigated the representations of rate in the auditory pathway of human
listeners using functional magnetic resonance imaging (fMRI), an indicator of population neural activity. Stimuli
were trains of noise bursts presented at rates ranging from low (1-2/s; each burst is perceptually distinct) to
high (35/s; individual bursts are not distinguishable). There was a systematic change in the form of fMRI response
rate-dependencies from midbrain to thalamus to cortex. In the inferior colliculus, response amplitude increased
with increasing rate while response waveshape remained unchanged and sustained. In the medial geniculate body,
increasing rate produced an increase in amplitude and a moderate change in waveshape at higher rates (from sustained
to one showing a moderate peak just after train onset). In auditory cortex (Heschl's gyrus and the superior temporal
gyrus), amplitude changed somewhat with rate, but a far more striking change occurred in response waveshape-low
rates elicited a sustained response, whereas high rates elicited an unusual phasic response that included prominent
peaks just after train onset and offset. The shift in cortical response waveshape from sustained to phasic with
increasing rate corresponds to a perceptual shift from individually resolved bursts to fused bursts forming a continuous
(but modulated) percept. Thus at high rates, a train forms a single perceptual "event," the onset and
offset of which are delimited by the on and off peaks of phasic cortical responses. While auditory cortex showed
a clear, qualitative correlation between perception and response waveshape, the medial geniculate body showed less
correlation (since there was less change in waveshape with rate), and the inferior colliculus showed no correlation
at all. Overall, our results suggest a population neural representation of the beginning and the end of distinct
perceptual events that is weak or absent in the inferior colliculus, begins to emerge in the medial geniculate
body, and is robust in auditory cortex.
===========================
Am J Psychiatry 2002 Nov;159(11):1830-40
Unmasking disease-specific cerebral blood flow abnormalities: mood challenge in patients with remitted unipolar
depression.
Liotti M, Mayberg HS, McGinnis S, Brannan SL, Jerabek P.
OBJECTIVE: Remitted major depressive disorder is a vulnerable clinical state, suggesting persistence of an underlying
disease diathesis between episodes. To investigate neural correlates of such risk and to identify potential depression
trait markers, euthymic unipolar patients in remission, acutely depressed patients, and never-depressed volunteers
were studied before and after transient sad mood challenge. METHOD: Common and differential changes in regional
blood flow among the groups relative to the baseline state were examined with [(15)O]H(2)O positron emission tomography
after provocation of sadness with autobiographical memory scripts. RESULTS: Mood provocation in both depressed
groups resulted in regional cerebral blood flow (rCBF) decreases in medial orbitofrontal cortex Brodmann's area
10/11, which were absent in the healthy group. In the remitted group, mood provocation produced a unique rCBF decrease
in pregenual anterior cingulate 24a. The main effects in healthy subjects, an rCBF increase in subgenual cingulate
Brodmann's area 25 and a decrease in right prefrontal cortex Brodmann's area 9, were not present in the depressed
groups. CONCLUSIONS: Mood challenge in unipolar euthymic patients in full remission unmasks an apparent depression
trait marker. The pattern of acute CBF changes is distinct from that seen in euthymic healthy volunteers and mirrors
the untreated depressed state seen during a major depressive episode and the pattern of change seen in depressed
patients. These findings suggest that disease-specific modifications of pathways mediating transient mood changes
are present in unipolar depression independent of clinical illness status. These findings have implications for
understanding the vulnerability of remitted patients for illness relapse.
==========================
Musical syntax is processed in Broca's area: an MEG study.
Maess B, Koelsch S, Gunter TC, Friederici AD
Nat Neurosci 2001 May 4:540-5
Abstract
The present experiment was designed to localize the neural substrates that process music-syntactic incongruities,
using magnetoencephalography (MEG). Electrically, such processing has been proposed to be indicated by early right-anterior
negativity (ERAN), which is elicited by harmonically inappropriate chords occurring within a major-minor tonal
context. In the present experiment, such chords elicited an early effect, taken as the magnetic equivalent of the
ERAN (termed mERAN). The source of mERAN activity was localized in Broca's area and its right-hemisphere homologue,
areas involved in syntactic analysis during auditory language comprehension. We find that these areas are also
responsible for an analysis of incoming harmonic sequences, indicating that these regions process syntactic information
that is less language-specific than previously believed.
==========================
Curr Biol 2000 Apr 6;10(7):383-92
Interhemispheric switching mediates perceptual rivalry.
Miller SM, Liu GB, Ngo TT, Hooper G, Riek S, Carson RG, Pettigrew JD.
Vision, Touch and Hearing Research Centre, Department of Physiology and Pharmacology, The University of Queensland,
Brisbane, 4072, Australia. s.miller@vthrc.uq.edu.au
BACKGROUND: Binocular rivalry refers to the alternating perceptual states that occur when the images seen by the
two eyes are too different to be fused into a single percept. Logothetis and colleagues have challenged suggestions
that this phenomenon occurs early in the visual pathway. They have shown that, in alert monkeys, neurons in the
primary visual cortex continue to respond to their preferred stimulus despite the monkey reporting its absence.
Moreover, they found that neural activity higher in the visual pathway is highly correlated with the monkey's reported
percept. These and other findings suggest that the neural substrate of binocular rivalry must involve high levels,
perhaps the same levels involved in reversible figure alternations. RESULTS: We present evidence that activation
or disruption of a single hemisphere in human subjects affects the perceptual alternations of binocular rivalry.
Unilateral caloric vestibular stimulation changed the ratio of time spent in each competing perceptual state. Transcranial
magnetic stimulation applied to one hemisphere disrupted normal perceptual alternations when the stimulation was
timed to occur at one phase of the perceptual switch, but not at the other. Furthermore, activation of a single
hemisphere by caloric stimulation affected the perceptual alternations of a reversible figure, the Necker cube.
CONCLUSIONS: Our findings suggest that interhemispheric switching mediates perceptual rivalry. Thus, competition
for awareness in both binocular rivalry and reversible figures occurs between, rather than within, each hemisphere.
This interhemispheric switch hypothesis has implications for understanding the neural mechanisms of conscious experience
and also has clinical relevance as the rate of both types of perceptual rivalry is slow in bipolar disorder (manic
depression).
==============================
PNAS | June 10, 2003 | vol. 100 | no. 12 | 7406-7411
Psychology
Mapping the genetic variation of executive attention onto brain activity
Jin Fan , John Fossella , Tobias Sommer , Yanghong Wu and Michael I. Posner ¶ ||
Sackler Institute for Developmental Psychobiology, Weill Medical College of Cornell University, New York, NY 10021;
Department of Neurology, University of Hamburg, 20246 Hamburg, Germany; Department of Psychology, Beijing University,
Beijing 100871, China; and ¶Department of Psychology, University of Oregon, Eugene, OR 97403
Contributed by Michael I. Posner, April 9, 2003
Brain imaging data have repeatedly shown that the anterior cingulate cortex is an important node in the brain network
mediating conflict. We previously reported that polymorphisms in dopamine receptor (DRD4) and monoamine oxidase
A (MAOA) genes showed significant associations with efficiency of handling conflict as measured by reaction time
differences in the Attention Network Test (ANT). To examine whether this genetic variation might contribute to
differences in brain activation within the anterior cingulate cortex, we genotyped 16 subjects for the DRD4 and
MAOA genes who had been scanned during the ANT. In each of the two genes previously associated with more efficient
handling of conflict in reaction time experiments, we found a polymorphism in which persons with the allele associated
with better behavioral performance showed significantly more activation in the anterior cingulate while performing
the ANT than those with the allele associated with worse performance. The results demonstrate how genetic differences
among individuals can be linked to individual differences in neuromodulators and in the efficiency of the operation
of an appropriate attentional network.
==========================
Proc R Soc Lond B Biol Sci 1998 Nov 22;265(1411):2141-8
A 'sticky' interhemispheric switch in bipolar disorder?
Pettigrew JD, Miller SM.
Vision, Touch and Hearing Research Centre, University of Queensland, St Lucia, Brisbane, Australia. j.pettigrew@vthrc.uq.edu.au
Despite years of research into bipolar disorder (manic depression), its underlying pathophysiology remains elusive.
It is widely acknowledged that the disorder is strongly heritable, but the genetics are complex with less than
full concordance in monozygotic twins and at least four susceptibility loci identified. We propose that bipolar
disorder is the result of a genetic propensity for slow interhemispheric switching mechanisms that become 'stuck'
in one or the other state. Because slow switches are also 'sticky' when compared with fast switches, the clinical
manifestations of bipolar disorder may be explained by hemispheric activation being 'stuck' on the left (mania)
or on the right (depression). Support for this 'sticky' interhemispheric switching hypothesis stems from our recent
observation that the rate of perceptual alternation in binocular rivalry is slow in euthymic subjects with bipolar
disorder (n = 18, median = 0.27 Hz) compared with normal controls (n = 49, median = 0.60 Hz, p < 0.0005). We
have presented evidence elsewhere that binocular rivalry is itself an interhemispheric switching phenomenon. The
rivalry alternation rate (putative interhemispheric switch rate) is robust in a given individual, with a test-retest
correlation of more than 0.8, making it suitable for genetic studies. The interhemispheric switch rate may provide
a trait-dependent biological marker for bipolar disorder.
=========================
Adv Exp Med Biol 2002;508:461-9
Vision as motivation: interhemispheric oscillation alters perception.
Pettigrew JD, Carter O.
Vision Touch and Hearing Research Centre, School of Biomedical Sciences, University of Queensland, Australia. j.pettigrew@vthrc.uq.edu.au
The well-recognised proclivity of primates for things visual can sometimes mislead us into thinking that a high
order visual process is taking place at a much earlier level of processing than it is. We illustrate this with
a new illusion, Bonneh's "motion-induced-blindness", that involves the intermittent disappearance and
reappearance of simple bright targets under the influence of a moving background. This perceptual oscillation is
strongly affected by the mood and impulsivity of the subject, in line with other evidence that this simple disappearance
and reappearance must be taking place at a high level of processing, perhaps at the level of the cerebral hemsipheres
themselves.
==========================
Brain Res 1999 Mar 13;821(2):383-91
Relations of hippocampal volume and dentate gyrus width to gonadal hormone levels in male and female meadow voles.
Galea LA, Perrot-Sinal TS, Kavaliers M, Ossenkopp KP.
Department of Psychology, University of British Columbia, 2136 West Mall, Vancouver, BC, Canada. lgalea@psych.ubc.ca
The present study examined hippocampal volume and dentate gyrus width and their relations to gonadal hormone levels
in adult male and female meadow voles, Microtus pennsylvanicus. Females were split into High and Low Estradiol
groups based on the median estradiol level. Males were similarly split into High and Low Testosterone groups. Contrary
to previous reports in wild meadow voles, there was no evidence of an overall sex difference in hippocampal volume.
However, when male-female comparisons were limited to High Testosterone males and Low Estradiol females a significant
sex difference in hippocampal volume favouring males did emerge. Hippocampal volume in males was related to testosterone
level, with High Testosterone males having significantly larger hippocampi than Low Testosterone males. Similarly,
there was a significant influence of plasma estradiol level on hippocampal volume and left dentate gyrus width,
with High Estradiol females having larger hippocampi and dentate gyrus width than Low Estradiol females. In addition,
consistent with previous findings in the laboratory rat, there were sex differences favouring males in right dentate
gyrus width. These findings show that there is a complex relationship between hippocampal volume, dentate gyrus
width and gonadal hormone levels in male and female meadow voles.
==========================
Am J Physiol 1997 Nov;273(5 Pt 2):R1683-9
Amygdala but not hippocampal lesions impair olfactory memory for mate in prairie voles (Microtus ochrogaster).
Demas GE, Williams JM, Nelson RJ.
Department of Psychology, Johns Hopkins University, Baltimore, Maryland 21218, USA.
Exposure to an unfamiliar male conspecific results in pregnancy interruption (i.e., the Bruce effect) in rodents.
Unlike most laboratory rodents, female prairie voles (Microtus ochrogaster) are induced into estrus by chemosensory
stimuli contained in the urine of male conspecifics while grooming the anogenital (A-G) region of unfamiliar males.
Female prairie voles maintain a brief "memory" for the stud male for 8-10 days after mating. Subsequent
exposure to the same mate within this 8- to 10-day window does not elicit A-G investigation by the female and pregnancy
block does not result. However, exposure to the original male after 10 days evokes A-G investigation and pregnancy
block. To determine the neuroanatomic area(s) involved in olfactory memory for mate, female voles received bilateral
electrolytic lesions of either the amygdala or hippocampus. Females were subsequently exposed to males for 48 h,
separated for 3 days, then reintroduced to their original mate for 24 h. Although pregnancy rate did not differ
among the experimental groups, a greater proportion of amygdala-lesioned females displayed pregnancy block when
reexposed to their previous mates compared with hippocampal- or sham-lesioned voles. Amygdala-lesioned voles also
displayed a greater number of A-G investigations compared with the other groups. Performance on olfactory tests
was not impaired. Taken together, these results suggest that the amygdala plays an important role in olfactory
memory for mate in prairie voles.
(IDM : link this to the reference to empathy and smell associated with the amygdala)
==========================
Proc Natl Acad Sci U S A 1990 Aug;87(16):6349-52
Evolution of spatial cognition: sex-specific patterns of spatial behavior predict hippocampal size.
Jacobs LF, Gaulin SJ, Sherry DF, Hoffman GE.
Department of Anthropology, University of Pittsburgh, PA 15260.
In a study of two congeneric rodent species, sex differences in hippocampal size were predicted by sex-specific
patterns of spatial cognition. Hippocampal size is known to correlate positively with maze performance in laboratory
mouse strains and with selective pressure for spatial memory among passerine bird species. In polygamous vole species
(Rodentia: Microtus), males range more widely than females in the field and perform better on laboratory measures
of spatial ability; both of these differences are absent in monogamous vole species. Ten females and males were
taken from natural populations of two vole species, the polygamous meadow vole, M. pennsylvanicus, and the monogamous
pine vole, M. pinetorum. Only in the polygamous species do males have larger hippocampi relative to the entire
brain than do females. Two-way analysis of variance shows that the ratio of hippocampal volume to brain volume
is differently related to sex in these two species. To our knowledge, no previous studies of hippocampal size have
linked both evolutionary and psychometric data to hippocampal dimensions. Our controlled comparison suggests that
evolution can produce adaptive sex differences in behavior and its neural substrate.
==========================
Proc Natl Acad Sci U S A 2001 Jun 5;98(12):6941-4
A larger hippocampus is associated with longer-lasting spatial memory.
Biegler R, McGregor A, Krebs JR, Healy SD.
Institute of Cell, Animal, and Population Biology, King's Buildings, University of Edinburgh, West Mains Road,
Edinburgh EH9 3JT, Scotland, United Kingdom.
Volumetric studies in a range of animals (London taxi-drivers, polygynous male voles, nest-parasitic female cowbirds,
and a number of food-storing birds) have shown that the size of the hippocampus, a brain region essential to learning
and memory, is correlated with tasks involving an extra demand for spatial learning and memory. In this paper,
we report the quantitative advantage that food storers gain from such an enlargement. Coal tits (Parus ater) a
food-storing species, performed better than great tits (Parus major), a nonstoring species, on a task that assessed
memory persistence but not on a task that assessed memory resolution or on one that tested memory capacity. These
results show that the advantage to the food-storing species associated with an enlarged hippocampus is one of memory
persistence.
==========================
Proc Natl Acad Sci U S A 2000 Apr 11;97(8):4398-403
Navigation-related structural change in the hippocampi of taxi drivers.
Maguire EA, Gadian DG, Johnsrude IS, Good CD, Ashburner J, Frackowiak RS, Frith CD.
Wellcome Department of Cognitive Neurology, Institute of Neurology, University College London, Queen Square, London
WC1N 3BG, United Kingdom. e.maguire@fil.ion.ucl.ac.uk
Structural MRIs of the brains of humans with extensive navigation experience, licensed London taxi drivers, were
analyzed and compared with those of control subjects who did not drive taxis. The posterior hippocampi of taxi
drivers were significantly larger relative to those of control subjects. A more anterior hippocampal region was
larger in control subjects than in taxi drivers. Hippocampal volume correlated with the amount of time spent as
a taxi driver (positively in the posterior and negatively in the anterior hippocampus). These data are in accordance
with the idea that the posterior hippocampus stores a spatial representation of the environment and can expand
regionally to accommodate elaboration of this representation in people with a high dependence on navigational skills.
It seems that there is a capacity for local plastic change in the structure of the healthy adult human brain in
response to environmental demands.
==========================
J Neurosci 2002 Nov 15;22(22):10009-17
Vestibular information is required for dead reckoning in the rat.
Wallace DG, Hines DJ, Pellis SM, Whishaw IQ.
Canadian Centre for Behavioural Neuroscience, University of Lethbridge, Lethbridge, Alberta, Canada T1K 3M4.
Dead reckoning is an on-line form of spatial navigation used by an animal to identify its present location and
return directly to a starting location, even after circuitous outward trips. At present, it is not known which
of several self-movement cues (efferent copy from movement commands, proprioceptive information, sensory flow,
or vestibular information) are used to compute homeward trajectories. To determine whether vestibular information
is important for dead reckoning, the impact of chemical labyrinthectomy was evaluated in a test that demanded on-line
computation of a homeward trajectory. Rats were habituated to leave a refuge that was visible from all locations
on a circular table to forage for large food pellets, which they carried back to the refuge to eat. Two different
probe trials were given: (1) the rats foraged from the same spatial location from a hidden refuge in the light
and so were able to use visual cues to navigate; (2) the same procedure took place in the dark, constraining the
animals to dead reckon. Although control rats carried food directly and rapidly back to the refuge on both probes,
the rats with vestibular lesions were able to do so on the hidden refuge but not on the dark probe. The scores
of vestibular reflex tests predicted the dead reckoning deficit. The vestibular animals were also impaired in learning
a new piloting task. This is the first unambiguous demonstration that vestibular information is used in dead reckoning
and also contributes to piloting.
==========================
Behav Brain Res 2002 Oct 17;136(1):201
Bilateral participation of the hippocampus in familiar landmark navigation by homing pigeons.
Gagliardo A, Odetti F, Ioale P, Bingman VP, Tuttle S, Vallortigara G.
Dipartimento di Etologia, Ecologia ed Evoluzione, Universita di Pisa, Via A.Volta 6, I-56126, Pisa, Italy
Recent findings indicate a different role of the left and right hippocampal formation (RHF) in homing pigeon navigational
map learning. However, it remains uncertain whether the left or the RHF may play a more important role in navigation
based on familiar landmarks. In the present study, we attempted to answer this question by experimentally releasing
control and left and right hippocampal ablated pigeons from familiar training sites under anosmia, to render their
navigational map dysfunctional, and after a phase-shift of the light-dark cycle, to place into conflict a pilotage-like
landmark navigational strategy and a site-specific compass orientation landmark navigational strategy. Both left
and right hippocampal ablated birds succeeded in learning to navigate by familiar landmarks, and both preferentially
relied on sun-compass based, site-specific compass orientation to home. Like bilateral hippocampal lesioned birds,
and in contrast to intact controls, neither ablation group adopted a pilotage-like strategy. We conclude that both
the left and RHF are necessary if pilotage-like, familiar landmark navigation is to be learned or preferentially
used for navigation.
===========================
J Neurosci 1996 Dec 15;16(24):8027-40
Dynamics of mismatch correction in the hippocampal ensemble code for space: interaction between path integration
and environmental cues.
Gothard KM, Skaggs WE, McNaughton BL.
Arizona Research Laboratories Division of Neural Systems, Memory and Aging, University of Arizona, Tucson, Arizona
85724, USA.
Populations of hippocampal neurons were recorded simultaneously in rats shuttling on a track between a fixed reward
site at one end and a movable reward site, mounted in a sliding box, at the opposite end. While the rat ran toward
the fixed site, the box was moved. The rat returned to the box in its new position. On the initial part of all
journeys, cells fired at fixed distances from the origin, whereas on the final part, cells fired at fixed distances
from the destination. Thus, on outward journeys from the box, with the box behind the rat, the position representation
must have been updated by path integration. Farther along the journey, the place field map became aligned on the
basis of external stimuli. The spatial representation was quantified in terms of population vectors. During shortened
journeys, the vector shifted from an alignment with the origin to an alignment with the destination. The dynamics
depended on the degree of mismatch with respect to the full-length journey. For small mismatches, the vector moved
smoothly through intervening coordinates until the mismatch was corrected. For large mismatches, it jumped abruptly
to the new coordinate. Thus, when mismatches occur, path integration and external cues interact competitively to
control place-cell firing. When the same box was used in a different environment, it controlled the alignment of
a different set of place cells. These data suggest that although map alignment can be controlled by landmarks,
hippocampal neurons do not explicitly represent objects or events.
==========================
Nature 1998 Nov 5;396(6706):75-7
Hippocampal lesions disrupt navigation based on cognitive maps but not heading vectors.
Pearce JM, Roberts AD, Good M.
School of Psychology, Cardiff University, UK. pearcejm@cardiff.ac.uk
Animals can find a hidden goal in several ways. They might use a cognitive map that encodes information about the
geometric relationship between the goal and two or more landmarks. Alternatively, they might use a heading vector
that specifies the direction and distance of the goal from a single landmark. Rats with damage to the hippocampus
have difficulty in finding a hidden goal. Here we determine which of the above strategies is affected by such damage.
Rats were required to swim in a water maze to a submerged platform, which was always at the same distance and direction
from a landmark. The platform and landmark remained in the same place for the four trials of each session, but
they were moved to a new position at the start of a session. Rats with damage to the hippocampus found the platform
more efficiently than did normal rats in the first trial of a session but, in contrast to normal rats, their performance
did not improve during a session. Our results indicate that hippocampally damaged rats are able to navigate by
means of heading vectors but not cognitive maps.
=========================
Learn Mem 2001 Nov-Dec;8(6):326-35
Verbal and nonverbal emotional memory following unilateral amygdala damage.
Buchanan TW, Denburg NL, Tranel D, Adolphs R.
Department of Neurology, Division of Cognitive Neuroscience, University of Iowa, College of Medicine, Iowa City,
Iowa 52242, USA. tony-buchanan@uiowa.edu
The amygdala is involved in the normal facilitation of memory by emotion, but the separate contributions of the
left and right amygdala to memory for verbal or nonverbal emotional material have not been investigated. Fourteen
patients with damage to the medial temporal lobe including the amygdala (seven left, seven right), 18 brain-damaged,
and 36 normal controls