Q about artificial and biological neural-nets

Joseph T. Devlin jdevlin at pollux.usc.edu
Mon Mar 1 15:52:08 EST 1993


lamontg at u.washington.edu writes:
>the hypothesis
>runs something along the lines of that the destruction of the connections
>between the neurons promotes the growth of new connections, and that the
>connections that are not re-established could be seen as being relics of

>then, he mentioned something which had been shown along these lines in
>artificial neural nets.  it was something along the lines of if you
>trained the neural net to behave in one way, that simply trying to
>retrain it to behave another way wasn't as effective as first "damaging
>it" (whatever that means) and then retraining it.

  Well, I'm not certain what models you are referencing but I'd be
interested in hearing more about them.
  The only related materials I am familiar with show opposite affects.
For instance, it's well known that in senile dementia neurons have
_dendritic_ deteriorization and this is well correlated to poorer
cognitive performance.  Buell & Coleman (1979) and Bertoni-Freddari
et al (1988, 1990) have shown that gradual impairment of connections
in normal and pathological aging is in part due to morphological
changes of the synapse.  They claimed that as connections were lost
a "compensatory" mechanism came into play to increase the length of
terminals so as to attempt to maintain the total synaptic surface area
in a region.  In a model of this process, Horn et al (1992) showed that
this led to a gradual deterioration of overall "cognitive" performance
rather than any ability to learn different knowledge - although I'm fairly
certain they didn't look for that, either.

							- Joe

*************************************************************************
Joseph Devlin                      * email: jdevlin at pollux.usc.edu
University of Southern California  *
Department of Computer Science     * "The axon doesn't think.
Los Angeles, CA 90089              *  It just ax."  George Bishop
*************************************************************************	


Buell & Coleman (1979) Dendritic growth in the aged human brain and
  failure of growth in senile dementia.  _Science_ 206:854-856.

Bertoni-Freddari, Meier-Ruge, Ulrich. (1988) Quantitative morphology of
  synaptic plasticity in the aging brain.  _Scanning Microsc._ 2:1027-1034.

Bertoni-Freddari, Fattoretti, Casoli, Meier-Ruge, Ulrich (1990)  
  Morphological adaptive response of the synaptic junctional zones
  in the human dentate gyrus during aging and alzheimer's disease.

Horn, Ruppin, Usher, Herrmann (1992)  Neural Network modeling of memory
  deterioration in alzheimer's disease.  (Must either be a TR or a preprint.
  I'm not sure where I got my copy but if you want a copy I could probably
  send one along.)



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