pre-print in neuroprose

[Neil Burgess]

FTP-host: archive.cis.ohio-state.edu
FTP-filename: /pub/neuroprose/burgess.hipmod.ps.Z

*****do not forward to other groups*****

Dear connectionists,
the following preprint has been put on neuroprose, contact 
n.burgess at ucl.ac.uk with any retrieval problems,  
--Neil


	    `A model of hippocampal function'

	Neil Burgess, Michael Recce and John O'Keefe
 	   Dept. of Anatomy, University College, 
		London WC1E 6BT, U.K.

The firing rate maps of hippocampal place cells recorded in a freely 
moving rat are viewed as a set of approximate radial basis functions over
the (2-D) environment of the rat. It is proposed that these firing 
fields are constructed during exploration from `sensory inputs' (tuning 
curve responses to the distance of cues from the rat) and used by cells 
downstream to construct firing rate maps that approximate any desired 
surface over the environment. It is shown that, when a rat moves freely 
in an open field, the phase of firing of a place cell (with respect 
to the EEG $\theta$ rhythm) contains information as to the relative 
position of its firing field from the rat. A model of hippocampal function 
is presented in which the firing rate maps of cells downstream of the 
hippocampus provide a `population vector' encoding the instantaneous 
direction of the rat from a previously encountered reward site, enabling 
navigation to it. A neuronal simulation, involving reinforcement only at 
the goal location, provides good agreement with single cell recording
from the hippocampal region, and can navigate to reward sites in open 
fields using sensory input from environmental cues. The system requires 
only brief exploration, performs latent learning, and can return to a goal
location after encountering it only once.

Neural Networks, to be published. 26 pages, 2Mbytes uncompressed.