Neural coding information sought

Mark Laubach laubach at biogfx.neuro.wfu.edu
Thu Dec 7 12:59:57 EST 1995


kevin at gaba.neurology.wisc.edu (Kevin Hellman) wrote:

>There seems to be a big debate in brain theory about temporal coding vs.
>frequency coding, etc.  It would appear that there are characteristics
>that are in common all over the brain, but the method of information processing
>varies at least slightly from one region to another.  Perhaps what is most
>interesting in the information processing that is secondary to direct
>stimulus input-- e.g. cortical activity and not just sensory activation.

Indeed!  One way to look empirically at time or freq codes is let the
data decide the issue for you.  Nonlinear signal processing methods
developed by researchers in the wavelets community, such as the best
basis method, matching pursuit, local discriminant bases, and
discriminant pursuit, allow one to assess the _time-frequency
structure_ of signals such as neural spike trains.  The only choice to
make is how to filter (i.e., smooth) the spike train prior to these
analyses.  If information, in the context of statistical pattern
recognition, is present in the data, these methods will find it.
Also, they give you insight into whether this info was encoded by time
(i.e., location of spikes), freq (i.e., oscillations), or both.

Also, I agree that we will probably find that differ areas use differ
methods of signalling, kind of like different languages.  I have found
this in studies that used simultaneous recordings in the cortex and
basal ganglia.  Moreover, it may be that individual neurons in a given
structure have their own way of speaking, kind of like dialects within
a local region of the world.  For example, in the striatum,
neighboring neurons are not equivalent units either in terms of the
statistics of their spike trains or in terms of their response
properties.

Lastly, the point on info processing being secondary is most
important.  It imples to me that we need to focus on events that may
not be externally observed (i.e., intrinsic events or triggers) and
that it will be more difficult to uncover the mechanisms used by
systems that are far removed from the primary input and outputs
"surfaces" of the brain/body.


-----------------------------------
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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