HIPPOCAMPAL PLACE CELLS CONNECTED BY HEBBIAN SYNAPSES CAN SOLVE SPATIAL PROBLEMS

We propose that a cognitive map can be stored in the synapses between the pyramidal cells of CA3 in the form of the pattern of synaptic stre nghths connecting them. The model requires only that there are place c ells in CA3 and that the connections between them are modifiable in a Hebbian manner. Given these suppositions, the synaptic strengths must evolve to represent the distance between firing centers of synapticall y connected place cells. We argue that this arrangement of synaptic we ights embodies all the formal properties of a map. We demonstrate that the information stored in such a structure is sufficient to solve sev eral classic spatial problems including finding shortest paths, and ne gotiating detours. It is clear that much of the physiology and anatomy necessary to more precisely characterize the model is not known at th is time. Nevertheless the model is robust under a variety of cell and connection densities. It also performs well under several different fu nctions relating distance to synaptic strength. What is most remarkabl e in the model is that it is a logical consequence of the several key anatomical and physiological properties of the CA3 region of rats. Whe ther this information is used by the rat is difficult to assess at thi s time. Regardless of the outcome of this question, the model has prom ising applications to the field of robot navigation. (C) 1997 Wiley-Li ss, Inc.