memory (and SOMs)

Matt Jones jonesmat at physiology.wisc.edu
Mon Feb 25 16:52:35 EST 2002


"yan king yin" <y.k.y@(dont spam)lycos.com> wrote in message news:<zqQd8.1307$XZ.204847 at news.xtra.co.nz>...

> The problem is that we have very little understanding of cortical circuits,
> so we cannot formulate a theory about long-term memory in the cortex,
> including any form of pre-processing. What is needed is a detailed
> map of cortical circuits. This is not easy, but if we want to understand
> the brain then its a prerequisite.

Well, we know a -little- about cortical circuitry (and by "we", i mean
other people who actually know about cortex, not myself). And there
are a number of theories about long-term memory in the cortex. Marr
had the classical work in the early 70's which, although probably
wrong in a number of specific details, laid the initial conceptual
threads that still run through current cortical modeling. More
recently Rolls has proposed
a theory for the transition from short-term (hippocampus and EC) to
long-term (cortex) storage.



> 
> According to one study, there are about 32 visual areas in the macaque
> visual cortex, connected by 305 connections. Now it seems that these
> visual maps cannot be the result of self-organization, so they must be
> genetically specified.


Wait, why can't they arise through self-organization? Not to step
right into the middle of the nature-vs-nurture mess again, but there
are plenty of experimental demonstrations that cortical circuitry
(e.g., receptive field maps) do reorganize in response to
environmental changes (e.g., the "classical" but grisly experiments
involving sewing kittens' eyes shut, and gluing monkeys' fingers
together, then recording changes in cortical receptive fields). I
think there's very clear evidence for an initial developmental program
(i.e., nature) as well as self-organization (e.g., nurture).



 >If this can happen to the visual cortex, the rest of
> the cortex might be organized this way too. By simple division we can
> estimate that there could be 100 to several hundreds of  "maps" in the
> cortex. That is the number of circuits we have to figure out!

True, it's a daunting task.  


Cheers,

Matt




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