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Freeman's Results

Leslie Kay lmk2 at garnet.berkeley.edu
Sat Feb 27 15:45:34 EST 1993


In article <erwin.730658248 at trwacs> erwin at trwacs.fp.trw.com (Harry Erwin) writes:
>
>--A comment by Dr. Andrew Jennings:
>
> .............
>"Down-loading" language.
>
>I'm very interested in your comments. It certainly doesn't seem sensible to
>download things when there is a large variety of response.
>
>In a system like the brain where we want to trade storage for speed, isn't it
>better to send intermediate results off to the parts of the brain that can 
>best interpret them?
>
>I don't think "downloading" is good for wide-variety response functions.
>
>Which leaves us the question of how its <really> done.
>
>

The brain doesn't "download".  It also doesn't act like a computer, 
sending off intermediate results, it seems to act as a whole, a system
which exhibits responses which can be interpreted as coherent, spatially
distributed electrical activity, only when the stimulus has meaning.
So, in some sense, one could extrapolate and view the system as sending
off intermediate results, because it seems to "know" when something is
familiar enough to want to pay attention in order to identify it.  In
attractor terms, it may be said (although not yet proved) that in the 
process of recognition the activity of the olfactory bulb is brought
closer and then into one "wing" of a global attractor, which is in
essence its "classification" of the odor into a general meaning-class,
not a chemical-class.  Something about its travels in that orbit may
be what defines or is exhibited by the spatial pattern of electrical
activity which is seen in the olfactory bulb.  See the most recent
issue of "The Internation Journal of Bifurcation and Chaos" for
Freeman's most recent iteration of his theory, also a tutorial for
non-neuroscientist engineers and such folk on the neurophysiology
involved.

Which still leaves the question of "how is it really done?"  I
don't know, I just read the shadows and speculate as to how it 
might best and most consistently be explained.  :-).


>
>--my response
>In the brain, the need is for rapid response to the sensory environment.
>To optimize that, the senses have to report on objects in the animal's
>internal model as directly as possible. Otherwise there's a lot of
>correlation that has to be done for each breath, each eye staccade, and 
>each sound. I speculate that "downloading" is performed in the olfactory
>system by the AON presenting synthetic sensory data to the "wet end" of
>the OB while pulling the back end of the OB to the hyperbolic point
>that the PPC uses as the starting point for processing when a breath
>is taken. The output of the entire system is a "noisy limit cycle"
>(NLC) that identifies the object being detected. This NLC consists
>of an underlying carrier wave modulated by the novel data associated
>with the object. This combined signal (which is evidenced to the cortex
>by a pattern of neurons that have become synchronized and periodic
>in their spike trains) is generated by either the OB or by the PPC.

I'm not sure if you're referring to neurons here in the physiological
sense or in the neural network sense, but since you mentioned "spike
trains" I am assuming the former.  Freeman's work doesn't rely on
individual neurons being synchronized, in fact, this is probably not
the case.  The synchronized activity is seen on the neural mass level.
The synchronization of summed activity is what is exhibited as 
correlation in the dominant wave form in the EEG.  There was a lot of
work done to address the issue of how the EEG is correlated with the
spike activity of the underlying neurons, but they are not really
synchronized or periodic.  The EEG is synchronized and periodic, however.

>If generated by the OB, the AON or the PPC has to simultaneously present
>the synthetic sensory data and the carrier wave during training. If
>generated by the PPC, then the PPC has to learn to correlate the output
>of the OB generated during training with the carrier wave to be used for
>that object.
>
>There are a number of ways to combine the carrier wave with the object
>data. One speculation is that the carrier wave is continuous, while the
>object data consists of bursts marking the components of the carrier wave
>where there was matching. It could be the other way around, too.

..................

>
>Cheers,
>-- 
>Harry Erwin
>Internet: erwin at trwacs.fp.trw.com
>

It is the pattern of electrical activity which is exhibited by the
OB (and probably higher centers) which is associated with the perception.
The carrier wave can, and does, vary, but the pattern remains fairly
constant.  Also, there is not a tremendous amount of difference in the
carrier waves between different odors for the same animal.  I believe
that there is more variability between animals and arousal states in
terms of the carrier wave, than between odors (or stimuli) in the same
animal.

Leslie Kay
lmk2 at garnet.berkeley.edu



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