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phase-locking in cochlea

Ron Blue rcb1 at LEX.LCCC.EDU
Mon Dec 2 10:41:48 EST 1996

On Thu, 28 Nov 1996, Bill Simpson wrote:
> Several fairly old papers (e.g. Evans, 1975; Rose et al 1968) show that
> cochlear nerve fibres fire in a phase-locked way.  They fire on the peaks.
> I was wondering if there are recent papers discussing how this is used for
> the coding of frequency in the brain.
This should interest you.
Subject: RE: long-range synchronous fast oscillations

Ron Blue's  response to:

>R D Traub, M A Whittington, I M Stanford
> & J G R Jefferys A mechanism for generation of
>long-range synchronous fast oscillations in the cortex
>Nature 382, 621-624 (1996) 
>Abstract:  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 remain 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
>timescale 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 millimeters,
>whereas they fire single spikes under other conditions. 
>Thus, know properties of neurons and local synaptic circuits
>can account for tightly synchronized oscillations in
>large neuronal ensembles.

more quoted out of context.

>oscillations can be coherent over distances of up to 7 mm,
>with zero or near-zero (<3ms) average phase lag.  Coherence
>of in-phase gamma oscillations has also been observed between
>primary and associational visual cortices, and across the
>corpus callosum, where antidromic axonal conduction delays
>are estimated to be 2.73 +/- 2.38 ms (ref 11).
>The coherent oscillation problem can be broken down into
>two questions: how do local circuits, or even individual
>cells, generate gamma-frequency oscillations, and what
>happens when oscillating local circuits are synaptically
Why would be a more interesting question.  The why is because
the nervious system is using reference wavelets to imbed
information.  The single spike activity is the information
and NOISE.  The double spike is instructional REFERENCE to
SET the REFERENCE frequency.  This means that you should
observe the double spike for olifaction, movement, vision,
hearing, etc.   The reason that low frequencies destroy gamma
is because lower reference frequencies exist.  The information
is a HIGH frequency over write on the carrier or reference frequency for
a particular FUNCTION.  Function frequencies would be the one's
already generated by research.

Also the formation of neural oscillons, correlational opponent-
process, phase shifting via wavelet distortion, and the TOTAL
reference of ALL interacting information would be important
to understanding what is happening.  Examples, illusions..

Also the WEIGHT and timing of the
information in the oscillation loops would be important
as suggest by Hempfling's equations

>A circuit model, using a 51-compartment axon/soma/dentritic
>model for each inter neuron, accounts for the observed
>properties of the network frequency on unitary inhibitory
>postsynaptic conductance and time course.  The model works
>when a sufficiently high synaptic connectivity exists.
>the model also correctly predicts a break-up of the network
>oscillation when a sufficently low frequency is attained.
>In simulations,eight interneurons are sufficient to generate
>synchronized gamma oscillations, when all-all connectivity
>exists.  In such small local circuits, axon conduction
>delays are probably negligible.
>This propert of doublet firing suggest a way that oscillators
>might be connected together with conduction delays and still
>oscillate coherently with near-zero phase lag.
>As doublet firing is reduced sufficiently, long-range correlations
>in the oscillations are attenuated.
I hope others will recognize the importance of this work even if
you disagree with my interpretation of its meaning.
Ron Blue

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