The Formation of Circularly Symmetric Place Fields in the Rodent Hippocampus.

Szabolcs Káli   Peter Dayan
Society for Neuroscience Abstracts, 28.


Abstract

Regions CA3 and CA1 of the rodent hippocampus contain cells whose activities are determined by spatial location. In open field environments, the firing rates of these place cells are largely independent of the direction the animal faces, although their main inputs come from areas that likely respond to combinations of sensory cues and whose outputs will therefore depend on head direction. We model how the recurrent network in CA3, in the face of Hebbian synaptic plasticity, can induce the approximately circularly symmetric structure of the place fields.

The model CA3 has two modes of operation, learning and recall. Switching between the modes might be accomplished by the action of neuromodulators like acetylcholine. In learning mode, the activities of CA3 neurons are determined in a purely feedforward manner by the mossy fiber inputs, which are tuned to both place and head direction. Hebbian learning takes place in both the perforant path inputs (which therefore come to represent the same mapping from entorhinal cortex to CA3 as the pathway through the dentate gyrus) and the CA3 intrinsic connections. In recall mode, the recurrent connections sculpt the feedforward input, making the cells direction independent.

Our results show how recurrent connections can account for the formation of circularly symmetric place fields, and allow us to determine the range of parameters which gives rise to this behavior.

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