The Involvement of Recurrent Connections in Area CA3 in Establishing the Properties of Place Fields: A Model

Szabolcs Káli and Peter Dayan
Gatsby Computational Neuroscience Unit

GCNU TR 1999-005 [October 1999]

Abstract
Strong constraints on the neural mechanisms underlying the formation of place fields in the rodent hippocampus come from the systematic changes in spatial activity patterns that are consequent on systematic environmental manipulations.  We describe an attractor network model of area CA3 in which local, recurrent, excitatory and inhibitory interactions generate appropriate place cell representations from location- and direction-specific activity in the entorhinal cortex.  The model has two modes of operation, learning and recall, which are switched under neuromodulatory control.   During learning, mossy fiber inputs impose activity patterns on CA3.  Then, through Hebbian plasticity in the recurrent excitatory connections, attractors in CA3 are sculpted appropriately, and through Hebbian plasticity in the perforant path inputs, entorhinal activity is associated with these attractors.  During recall, the spatial characteristics of the place fields are controlled by the way that the perforant path input selects amongst the attractors.  Depending on the training experience provided, the model generates place fields that are either directional or non-directional, and which change in accordance with experimental data when the environment undergoes simple geometric transformations.  Representations of multiple environments can be stored and recalled with little interference, and these have the appropriate degrees of similarity in visually similar environments.

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