Reconsideration of the role of the hippocampus in learned inhibition

The purpose of this article is to reconsider the role of the hippocampus in learning tasks that require suppression or prevention of memories or respo nses. This type of learning has generally been referred to as inhibitory le arning. Although early theories proposed that the hippocampus was important for inhibitory learning, these ideas have generally fallen out of favor. H owever, new developments in the conceptual understanding of inhibition alon g with recent experimental evidence require that we review these conceptual changes with regard to hippocampal function. We review three general categ ories of 'inhibition' that have been used with reference to hippocampal fun ction: neural inhibition, inhibition of attention and associative or learne d inhibition. We then consider recent developments in the field of animal l earning that call for changes in the early conceptualizations of learned in hibition. Specifically, current findings suggest that different types of le arning paradigms can yield conditioned inhibitors that are embedded in diff erent associative structures, at least some of which can co-exist with cond itioned excitation. Next we proceed to review a number of recent experiment s from our laboratory as well as others that encouraged renewed interest in the role for the hippocampus in inhibitory learning. We then conclude by c onsidering some of the implications of the idea that the hippocampus is inv olved with performance of conditioned responses based on cues that are conc urrently embedded in inhibitory and excitatory associations. (C) 2001 Elsev ier Science B.V. All rights reserved.