The hippocampus and the classically conditioned nictitating membrane response: A real-time attentional-associative model

Abstract

The present study introduces an attentional-associative model that incorporates (1) a mechanism capable of establishing associations between conditioned stimuli (CSs) and unconditioned stimuli (USs) and between two CSs; (2) a mechanism that, by combining CS-CS and CS-US associations, is capable of building a “computational cognitive map”; (3) a real-time version of Pearce and Hall’s (1980) attentional rule; (4) performance rules that convert learning variables into a topography of the rabbit’s nictitating membrane (NM) response; and (5) rules that convert learning variables into neuronal firing. The present study tested the “aggregate prediction” hypothesis as applied to hippocampal function. This hypothesis assumes that (1) the effect of hippocampal lesions (HL) is an impairment in the integration of the aggregate prediction used to compute attentional variables; (2) the effect of the induction of hippocampal long-term potentiation (LTP) is an increase in the value of the aggregate prediction by way of increasing the value of CS-CS associations; and (3) neural activity in the hippocampus is proportional to the instantaneous value of the aggregate prediction. In addition, the present study tested the hypothesis that medial septum activity is proportional to the value of attentional variables. Computer simulations for the HL case were carried out for acquisition under different interstimulus intervals, discrimination reversal, and sensory preconditioning. Computer simulations for the LTP case were carried out for discrimination acquisition. In addition, simulations of hippocampal unit activity during acquisition and extinction, and medial septum unit activity during the acquisition of conditioning, are presented. The aggregate prediction hypothesis proved capable of simulating most, but not all, experimental data regarding hippocampal manipulations in the rabbit’s NM response preparation. © 1988, Psychonomic Society, Inc.. All rights reserved.