neural coding of behavior: evidence for precise timing of spikes ?

Mark Laubach laubach at biogfx.neuro.wfu.edu
Mon Dec 11 16:21:11 EST 1995


rcb1 at LEX.LCCC.EDU (Ron Blue) wrote:

>Assume for that your brain is like a radio.  If you remain on the
>same station learning would be restrained.  If you change frequency 
>channels learning would be enchanced.  If you remember which channel
>you were one when you learned something new you could store the information
>under that reference frequency and modulation timing.

>Therefore, to function effectively you would need variation, and precise
>timing.  Ron Blue

This is a good metaphor.

I guess I've been a bit too harsh on the _precise timing_ thing.  I
should have been more clear.  Indeed, precise timing may be a real
basis for coding info in the brain.  Its just that I have found that
precisely timed patterns do not show up consistently over trials in a
behavioral task.  Nevertheless, this is really not evidence against
precise timing in neurotransmission.  Rather, the complexity of inputs
to a neuron may give rise to many precisely timed patterns and these
patterns may be the basis of the "richness" that allows for
flexibility in the CNS.

Moreover, I found that, for neurons in the rat basal ganglia and
cerebral cortex, there are trials, in a reaction-time task, on which
the neurons fail to fire at all.  This occurs for cells that fire
phasically even at high rates (from less than 5 to nearly 100 Hz)!
These same sorts of failures occur if I 'build' spike trains from
Poisson processes.  Maybe these failures are a basic limitation for
information transmission in the CNS.  Could it be that info trans is
limited by the poissonian nature of the generators underlying spike
activity?

(I doubt that I am the first to say of such a thing. Does anyone know
of refs for previous statements like mine above from the
neurophysiological or computational literature?)



-----------------------------------
Mark Laubach
Dept. of Physiology & Pharmacology
Bowman Gray School of Medicine
Wake Forest University
Winston-Salem, NC 27157
laubach at biogfx.neuro.wfu.edu
-----------------------------------




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