The hippocampus and inhibitory learning: a 'Gray' area?

Gray's approach to understanding hippocampal functioning [The Neuropsychology of Anxiety: An Enquiry into the Function of the Septo-hippocampal System, 1982; The Neuropsychology of Anxiety, 2000] departs from the prevailing view of that structure as a substrate for memory. Instead, Gray and McNaughton have proposed that hippocampus is involved with a function that is more fundamental than memory, namely the resolution of conflict between competing approach and avoidance tendencies. The present paper attempts to advance this perspective by describing how the effects of selective lesions of the hippocampus on performance in both relatively simple Pavlovian conditioning tasks and in more complex radial maze problems could be a consequence of an impairment in a simple form of inhibitory learning. Specifically, we consider the idea that the hippocampus is needed to form simple inhibitory associations between events that are concurrently embedded in simple excitatory associations [Behav Brain Res 119 (2001) 111]. This idea is compared with the conflict resolution hypothesis offered by Gray and McNaughton and avenues of integration are noted. In addition, the potential role for inhibitory learning in hippocampal-dependent spatial and contextual information processing is also discussed.