Neural networks and brain function

[Ken Harris]

I'd like to add something to the debate about neural network 
modelling and brain function, in particular concerning the 
resolution of apparently conflicting models.

It seems to me that the main contribution of neural networks to 
this question has been a change of emphasis.  Before neural 
networks were common currency, a neurological model usually 
consisted of a statement that a particular brain structure 
was necessary for a particular type of task.  For example:

     "The cerebellum is necessary for motor control" 
     "The hippocampus is necessary for spatial function" 
     "The hippocampus is necessary for episodic memory"

After neural networks, we have a different set of analogies.  
We now make neurological models that ascribe a particular
computational function to a brain structure.  For example:

     "The cerebellum performs supervised learning" 
     "The hippocampus functions as an autoassociative memory"

By talking about a computational function, rather than a 
type of task that a brain structure is needed for, a
lot of apparent conflict can suddenly be resolved.

In the example of the cerebellum, the evidence that the cerebellum
is involved in motor control and classical conditioning, and
even higher cognitive functions does not seem so contradictory.
It is very plausible that a supervised learning network
would be useful for all of these functions -- see for example
the work of Kawato and Thompson.

In the example of the hippocampus, work by Michael Recce and 
myself has shown how an autoassociative memory can play a role
in both episodic memory and spatial function, in particular 
giving an animal localisation ability by performing pattern 
completion on partial egocentric maps.  For those who might be 
interested:

Recce, M. and Harris, K.D. "Memory for places:  A navigational model
in support of Marr's theory of hippocampal function"  Hippocampus, vol
6, pp. 735-748 (1996)

http://www.ncrl.njit.edu/papers/hpc_model.ps.gz


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Ken Harris
Department of Anatomy and Developmental Biology
University College London
http://www.anat.ucl.ac.uk/~kdh