A MODEL OF HIPPOCAMPAL FUNCTION

The firing rate maps of hippocampal place cells recorded in a freely m oving rat are viewed as a set of approximate radial basis functions ov er the (2-D) environment of the rat. It is proposed that these firing fields are constructed during exploration from ''sensory inputs '' (tu ning curve responses to the distance of cues from the rat) and used by cells downstream to construct firing rate maps that approximate any d esired surface over the environment. It is shown that, when a rat move s freely in an open field, the phase of firing of a place cell (with r espect to the EEG theta rhythm) contains information as to the relativ e position of its firing field from the rat. A model of hippocampal fu nction is presented in which the firing rate maps of cells downstream of the hippocampus provide a ''population vector'' encoding the instan taneous direction of the rat from a previously encountered reward site , enabling navigation to it. A neuronal simulation, involving reinforc ement only at the goal location, provides good agreement with single c ell 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.