[Comp-neuro] Review announcement

jim bower bower at uthscsa.edu
Wed Jul 23 11:50:48 CEST 2008


I see your vino and raise you two caipirinhas. ;-)


"Ease of propegating synchronous signals". Doesn't this fundamentally depend on neurons essentially being temporal / spatial summing devices?  Which they aren't at least not the ones I deal with. 

BTW when I suggest that oscillations are epiphenomina, I mean when recorded at the level of extracellular field potentials. I have no doubt myself that the brain and neurons care about periodicity. This is clear as has been pointed out here already in the periodic behavior of motor systems and therefore the neurons that coordinate movement (CPGs).   

My personal suspicions revolve around the specific significance of synchrony, which it seems to me is inevitably tied to an integrate and fire assumption about neuronal processing (and core therefore to most abstract models of neurons and networks). 

With respect to "noise" again, I personally thing the term should be banned or barring that, we should agree on a common definition which is surprisingly hard to do even in computational neuroscience. 

Finally, the most tightly regulated (I.e. Neuronal event associated with the largest number and probably most complex ion channels) is spike initiation and in particular, the regulation of spike to spike firing patterns. Doesn't that suggest that the timing of individual spikes and spike trains is critical to signal transduction?  This is what raises concern for me when I am told that neurons are intrinsically noisy devices. They sure spend a lot of energy controlling the timing of their outputs. 

Jim
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-----Original Message-----
From: "G. Bard Ermentrout" <bard at math.pitt.edu>

Date: Tue, 22 Jul 2008 15:22:43 
Cc: <comp-neuro at neuroinf.org>; <comp-neuro-bounces at neuroinf.org>
Subject: Re: [Comp-neuro] Review announcement


For what it is worth - I have puzzled over the ubiquity of oscillations in 
the CNS and still wonder what they are good for. Jim and others argue 
epiphenomena, and this could still be correct, but it is real hard for me 
to believe that nature would ignore a free byproduct like this.  One thing 
about oscillations is that they have associated with them a zero 
eigenvalue at the single cell, microcircuit or other level and what this 
does is it makes it very eay to modulate the timing of their spikes. Much 
more so than with fixed points. Thus it very easy from the point of view 
of efficiency to move the spikes around in sych a way as to e.g. compute 
correlations via the stochastic synchrony mechanism and thus propagate 
feedfoward synchronous or correlated activity to other areas or layers. 
Synchrony or near synchrony is very efficient at propagating in 
feedforward networks.  Oscillations make it real easy to read out 
correlations and also make it very easy to quickly desynchronize groups 
with simple modulation of their intrinsic dynamaics - e.g. ACh  which can 
greatly affect how a neuron responds to the timing of an input and to 
other neurons to which it is attached.

>From Rome with one vino too many,

bard Ermentrout

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