In article <1992Jun28.201116.23454 at rhrk.uni-kl.de> andrick at sun.rhrk.uni-kl.de (Ulf Andrick [Biologie]) writes:
>There was an article in Spektrum der Wissenschaften (German version of
>Scientific American) in May 1989 by Braitenberg and Schuez in which
>the authors suggested that the connections between the pyramid cells in the
>cerebral cortex are stochastically distributed, so that there is no special
>preformed structure. I'm curious to know if this view is commonly shared by
>brain physiologists or if it is already out-dated because of newer findings.
The best summary of the data available to date that addresses the above
question (and cortical circuitry in general) has been written by
Edward White (1989) "Cortical Circuits." Ed White is one of a few people
carrying out experiments that directly address questions of specificity
of connections at the microcircuitry level.
The short answer to your question is yes and no. That is, stochastic
is not equivalent to random. Within a particular layer (connectivity to,
from, and between different layers in the cortex is very specific) there
seems to be a stochastic distribution of connections. Stochastic
signifies a randomly determined series of observations, each of which
is a single element that belongs to a population that obeys a deterministic
distribution. Therefore there does seem to be structure and specificity
to the microcircuitry.
Usually, when connections in the brain are labeled random you can
replace the word 'random' with 'unknown.' When actual data are gathered
the connections that were thought to be random are typically found to be highly
specific. Experiments on the microcircuitry of the brain are extremely
difficult and the number of cells/connections studied are very few. (We
are talking about the reconstruction of only a *few* neurons out of
how many in the brain?) Nevertheless, it is interesting that there is
specificity even at the microcircuitry level, although apparently
stochastic.
Don
P.S. This is necessarily just a reflection of my personal musing on the
subject. Ed White's book cited above is highly recommended if
you want the data and opinions of a master on the subject. Also,
the book may easily be read by non-neuroscience professionals.
-------------------------------------------------------------------------------
Donald Doherty
Dept. of Psychobiology Email: ddoherty at ics.uci.edu
University of California CompuServe: 76646,1321
Irvine, CA 92717-4550 FAX: (714) 725-2447
U.S.A. Voice: (714) 856-1776
