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Cortical Architectures

Ken Easlon ken at giskard.holonet.net
Sat Mar 5 09:47:44 EST 1994

lmk2 at garnet.berkeley.edu (Leslie Kay) writes in 
<2l6e56$nrn at agate.berkeley.edu>

> Harry Erwin <erwin at trwacs.fp.trw.com> wrote:
>> Does anyone have a clue on why the paleocortex has 3 layers and
>> the neocortex, 6? In the work I've been doing with models of the
>> olfactory system, the three layers appear to have input,
>> processing, and output as their functions, but then I'm a dumb
>> engineer...

> I would guess that more and more differentiated input and output
> demands, as well as the more complicated demands of the newer
> senses (olfaction being evolutionarily the oldest in mammals),
> would demand more layers, more cells, more processing
> capabilities.

Wickelgren, basing his conjecture on the work of Palm and
Braitenberg, believes that 

     the basal dendrites of cortical pyramidal cells are 

          "metric" (meaning the probability of a synaptic
          connection decreases with distance), 

          and form innate binding links (in the lower cortical
          layers) within cell assemblies which cause all the
          neurons in the cell assembly to be activated together.

     and the apical dendrites of pyramidal cells (which branch in
     the upper cortical layers) are 

          both metric and ametic (probability of synaptic
          connections independent of distance)

          and form learned or associative links with both nearby
          and remote areas or the cortex, and can be connected or
          "erased" as learning develops.

It would seem to me, from an engineering standpoint, more upper
layers would give a greater capability for "long distance
communication" and wide area "calling circles" (my wording), and
hence a greater repertoire of ideas (which Wickelgren describes as
any unit of representation such as sensory or motor features,
segments, images, concepts, propositions, actions, or mental

In my view, the evolutionary advantage of a larger repertoire of
ideas in each individual would be a faster (and more competitive)
ability for the species to recognize and deal with threats and
opportunities, and thus to dominate a wider range of ecological

Any merit to this thinking?

               Concepts in Neuroscience, Vol. 3, No. 1 (1992) 1-53
               Wayne A. Wickelgren, Psychology Department
               Columbia University, New York, NY 10027, USA
Ken Easlon
ken at holonet.net

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