The involvement of recurrent connections in area CA3 in establishing the properties of place fields: a model

Strong constraints on the neural mechanisms underlying the formation of pla ce fields in the rodent hippocampus come from the systematic changes in spa tial activity patterns that are consequent on systematic environmental mani pulations. We describe an attractor network model of area CA3 in which loca l, recurrent, excitatory, and inhibitory interactions generate appropriate place cell representations from location- and direction-specific activity i n the entorhinal cortex. In the model, familiarity with the environment, as reflected by activity in neuromodulatory systems, influences the efficacy and plasticity of the rec urrent and feedforward inputs to CA3. In unfamiliar, novel, environments, m ossy fiber inputs impose activity patterns on CA3, and the recurrent collat erals and the perforant path inputs are subject to graded Hebbian plasticit y. This sculpts CA3 attractors and associates them with activity patterns i n the entorhinal cortex. In familiar environments, place fields are control led by the way that perforant path inputs select among the attractors. Depending on the training experience provided, the model generates place fi elds that are either directional or nondirectional and whose changes when t he environment undergoes simple geometric transformations are in accordance with experimental data. Representations of multiple environments can be st ored and recalled with little interference, and these have the appropriate degrees of similarity in visually similar environments.