On 5 Aug 2002 23:30:44 +0100, rcb5 at msn.com ("Ron Blue") wrote:
>> Kenneth Collins wrote in message ...
>> >mat wrote in message
>> ><43525ce3.0208050245.702a29ca at posting.google.com>...
>> >>[...]
>> >>You claim the natural tendency of neural tissue is to
>> >>minimize excitation, whereas in fact quite the opposite is true
>> >>(see the work of Traub et al.).
>> >
>> >Got a specific ref[?] ("anyone, anyone anyone[?"] :-)
>>Traub et al (1996) reported that the brain would coherently oscillate within
>two milliseconds after a doublet spike that allows synchronous neuronal
>oscillations in the 30-70 hertz range. The coherent synchronous oscillation
>will occur over large distance. Oscillations slower that 30-hertz will cause
>the system to become discoherent.
>>Traub, R.D.; Whittington, M.A.; Stanford, I.M.; & Jefferys, J.G.R.
>(1996) A mechanism for generation of long-range synchronous fast
>oscillations in the cortex. Nature 382, 621-624
Nature 1996 Oct 17;383(6601):621-4
A mechanism for generation of long-range synchronous fast oscillations
in the cortex.
Traub RD, Whittington MA, Stanford IM, Jefferys JG.
IBM Research Division, T. J. Watson Research Center, Yorktown Heights,
New York 10598, USA.
Synchronous neuronal oscillations in the 30-70 Hz range, known as
gamma oscillations, occur in the cortex of many species. This
synchronization can occur over large distances, and in some cases over
multiple cortical areas and in both hemispheres; it has been proposed
to underlie the binding of several features into a single perceptual
entity. The mechanism by which coherent oscillations are generated
remains unclear, because they often show zero or near-zero phase lags
over long distances, whereas much greater phase lags would be expected
from the slow speed of axonal conduction. We have previously shown
that interneuron networks alone can generate gamma oscillations; here
we propose a simple model to explain how an interconnected chain of
such networks can generate coherent oscillations. The model
incorporates known properties of excitatory pyramidal cells and
inhibitory interneurons; it predicts that when excitation of
interneurons reaches a level sufficient to induce pairs of spikes in
rapid succession (spike doublets), the network will generate gamma
oscillations that are synchronized on a millisecond time-scale from
one end of the chain to the other. We show that in rat hippocampal
slices interneurons do indeed fire spike doublets under conditions in
which gamma oscillations are synchronized over several millimetres,
whereas they fire single spikes under other conditions. Thus, known
properties of neurons and local synaptic circuits can account for
tightly synchronized oscillations in large neuronal ensembles.
PMID: 8857537 [PubMed - indexed for MEDLINE]
http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8857537&dopt=Abstract
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FULL PAPER FOR FREE: http://www.pnas.org/cgi/content/full/94/22/12198
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Proc Natl Acad Sci U S A 1997 Oct 28;94(22):12198-203
Recurrent excitatory postsynaptic potentials induced by synchronized
fast cortical oscillations.
Whittington MA, Traub RD, Faulkner HJ, Stanford IM, Jefferys JG.
Department of Physiology and Biophysics, Imperial College School
of Medicine at St. Mary's, London W2 1PG, United Kingdom.
m.whittington at sm.ic.ac.uk
Gamma frequency (about 20-70 Hz) oscillations occur during novel
sensory stimulation, with tight synchrony over distances of at least 7
mm. Synchronization in the visual system has been proposed to reflect
coactivation of different parts of the visual field by a single
spatially extended object. We have shown that intracortical
mechanisms, including spike doublet firing by interneurons, can
account for tight long-range synchrony. Here we show that synchronous
gamma oscillations in two sites also can cause long-lasting (>1 hr)
potentiation of recurrent excitatory synapses. Synchronous
oscillations lasting >400 ms in hippocampal area CA1 are associated
with an increase in both excitatory postsynaptic potential (EPSP)
amplitude and action potential afterhyperpolarization size. The
resulting EPSPs stabilize and synchronize a prolonged beta frequency
(about 10-25 Hz) oscillation. The changes in EPSP size are not
expressed during non-oscillatory behavior but reappear during
subsequent gamma-oscillatory events. We propose that
oscillation-induced EPSPs serve as a substrate for memory, whose
expression either enhances or blocks synchronization of spatially
separated sites. This phenomenon thus provides a dynamical mechanism
for storage and retrieval of stimulus-specific neuronal assemblies.
PMID: 9342386 [PubMed - indexed for MEDLINE]
http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9342386&dopt=Abstracthttp://IanGoddard.net
Something can come from nothing if, and only if,
that something is equal to nothing ((+)+(-)) = 0.
