memory (and SOMs)

mat mats_trash at
Wed Feb 27 08:45:30 EST 2002

> Braitenberg and Schuz have done some statistical analysis of the cortex,
> and they found that most parts of the neocortex are organized into
> discrete "patches" with parallel projections connecting them. Therefore
> one thing for sure is that cortical connections are not diffuse (as least
> in the neocortex). My point is that these discrete connections between
> patches are specified by genes, ie not altered by experience under
> normal circumstances. For example in the visual cortex you have areas
> V1, V2, V4 and MT connected by specific pathways that do not vary
> from individual to individual (as least such has not been reported). As
> pointed out by Matt Jones, there are exceptional situations where
> cortical reorganization does take place -- see my reply to him.
> Personally I am inclined to the view that large scale cortical pathways
> connecting the "patches" are genetically determined, I'll explain this
> in Matt Jones thread as well.

I also have Braitenberg and Schulz's book, and was very surprised to
note that much of the data implied the difference between the human
brain and that of say the rat seemed to be th actual amount of neural
tissue, but that per unit volume the tissue was reasonably similar
between species.  I have not read it in detail though yet (still
recovering from the cost!)  Further I totally agree that genes encode
the proteins which act as growth factors and receptors (and other
interactions) in forming synapses.  Through evolution the regulation
of expression of different growth-guiding mechanism in different brain
regions has been tuned so that neuronal connectivity is broadly
similar across individuals of the same species. However, I would again
stress that the environment must play a critical role in determining
these connections.  Evolution only works within the environment of the
organism and so the genetic development that has occured to give us
the precise connectivity will have been selected by our environment
and thus will be critically dependent on it. Also I would imagine that
though broadly similar, the detail of the connectivity might be quite
variable, again an arena in which environment (in its widest and
broadest sense) may play a critial role.

> Also Im still writing my reply to your SOM idea, please be patient.

I look forward to it! :)

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