The hippocampus and motivation revisited: appetite and activity.

After reviewing the available data regarding the various effects of manipulating (e.g. lesions, chemical or electrical stimulation) the hippocampal formation, Jarrard concluded that this structure likely played a role in motivated behaviors, specifically in general behavioral activation and incentive motivation. Since that time there have been technical advances in lesion techniques and conceptual advances in theories of motivation and learning. Here, we present more recent data that demonstrates the effects of hippocampal lesions on general activity, the utilization of interoceptive state cues, ingestive behaviors, and appetitive responding. We critically evaluate several theories of hippocampal function that have been proposed to explain these data, including the hippocampus as an inhibitor of general activation, as a processor of energy state signals and as a mediator of reward valuation. Finally, we propose that these findings may also be accounted for based on a role for the hippocampus in the learned inhibition of appetitive behaviors. We conclude that, while the specific mechanism of hippocampal involvement may not yet be determined, it is clear that this structure is involved in food-related behaviors and we caution researchers to consider this as a possible confound in studies of learning and memory processes.