[Neuroscience] Re: Wherefore art thou Neuron Code?

r norman via neur-sci%40net.bio.net (by r_s_norman from _comcast.net)
Mon Apr 2 08:00:55 EST 2007


On Mon, 2 Apr 2007 07:46:37 -0400, "Glen M. Sizemore"
<gmsizemore2 from yahoo.com> wrote:

>
>"John H." <bingblat from goaway.com.au> wrote in message 
>news:461097d6 from quokka.wn.com.au...
>> It's Only A Game Of Chance: Leading Theory Of Perception Called Into
>> Question
>> Science Daily - The validity of a leading theory that has held a glimmer 
>> of
>> hope for unraveling the intricacies of the brain has just been called into
>> question. Dr. Ilan Lampl of the Weizmann Institute of Science's 
>> Neurobiology
>> Department has produced convincing evidence to the contrary. His findings
>> recently appeared in the journal Neuron.
>>
>> http://www.sciencedaily.com/releases/2007/03/070327144225.htm
>>
>>
>"According to the theory, the brain is able to discriminate between, say, a 
>chair and a table because each of them will generate a distinct sequence of 
>patterns within the neural system that the brain then interprets."
>
>
>
>Let's assume for a moment that chairs and tables are "distinct patterns." 
>Then the question becomes "How do the distinct patterns we call 'chair' and 
>'table' come to produce these different responses?" Notice that the common 
>theory is simply that the difference in the patterns are somehow preserved 
>in the brain. But how does this explain anything? We now have to explain how 
>the differences in pattern "in the brain" explain the differences in 
>response. If this was a legitimate question when the "patterns" were out in 
>the environment, why is it not a legitimate question when the pattern is "in 
>the brain"? I won't comment extensively on the rest of the blurb because not 
>enough information is given about what was done other than to say that 
>Skinner always used to say things like "The pattern of stimulation on the 
>retina is quickly lost in the nervous system" (this is a paraphrase). I 
>began to think that he was just a bit behind the times, and my criticism of 
>representationalism focused on the fact that 1.) "representation" must be 
>functionally-defined (i.e. a "mapping is not necessarily a "representation" 
>and 2.), that the presence of "mappings" in the brain does no more to 
>explain seeing than patterns in the world. Now it seems that even the notion 
>of a consistent mapping may be bullshit. As I have said many times, despite 
>the arm-breaking self-back-patting of neuroscientists (especially those that 
>are concerned with behavior) we are about at the level where we have a 
>more-or-less complete description of habituation of the gill-withdrawal 
>reflex in Aplysia. The general point to be made is that, in many, many cases 
>in neuroscience, behavior hasn't been broken down into the right analytical 
>units - that is, the conceptual structure inherited from mainstream 
>psychology is, literally, nonsense. Note that, despite Kandel's careless 
>language, "habituation" is conceptually clean.

I had similar reservations but then I realized I was criticizing a
press release, not a real paper.   The paper must be

  Mokeichev A, Okun M, Barak O, Katz Y, Ben-Shahar O, Lampl I.
  Stochastic emergence of repeating cortical motifs in 
  spontaneous membrane potential fluctuations in vivo.
  Neuron. 2007 Feb 1;53(3):413-25
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?itool=abstractplus&db=pubmed&cmd=Retrieve&dopt=abstractplus&list_uids=17270737

with comment in Neuron. 2007 Feb 1;53(3):319-21
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=17270729&itool=pubmed_docsum

I haven't yet read the full paper to see how much of the press release
nonsense was even suggested there. The abstract of the paper, itself,
says:

It was recently discovered that subthreshold membrane potential
fluctuations of cortical neurons can precisely repeat during
spontaneous activity, seconds to minutes apart, both in brain slices
and in anesthetized animals. These repeats, also called cortical
motifs, were suggested to reflect a replay of sequential neuronal
firing patterns. We searched for motifs in spontaneous activity,
recorded from the rat barrel cortex and from the cat striate cortex of
anesthetized animals, and found numerous repeating patterns of high
similarity and repetition rates. To test their significance, various
statistics were compared between physiological data and three
different types of stochastic surrogate data that preserve dynamical
characteristics of the recorded data. We found no evidence for the
existence of deterministically generated cortical motifs. Rather, the
stochastic properties of cortical motifs suggest that they appear by
chance, as a result of the constraints imposed by the coarse dynamics
of subthreshold ongoing activity.






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