Hippocampal regulation of aversive memories

Abstract

For many years, the hippocampal formation has been implicated in the regulation of negative emotion, yet the nature of this link has remained elusive. Recent studies have made important links between the hippocampus and regulation of stress hormones that affect aversive memory. Additional studies have shown that the hippocampus regulates the gating of fear by contextual information. An emerging literature also links the hippocampus to prediction errors during fear learning and extinction. The mechanisms by which the hippocampus regulates negative emotion are clearly complicated, but suggest that interventions aimed at restoring normal hippocampal function may help with disorders of negative affect, such as depression or post-traumatic stress disorder and depression.

Figure 1. Diverse mechanisms for hippocampal enhancement of aversive memory

The hippocampus controls fear and anxiety through multiple mechanisms, including the regulated secretion of stress hormones, the facilitation of associations between environmental context and aversive outcomes, the enabling of context-dependent expression of fear extinction, and the enhancement of fear learning via prediction errors. The hippocampus may perform these roles by direct or indirect connections with circuits mediating aversive memory.

Figure 2. Sources of hippocampal prediction errors

The hippocampus participates in many forms of prediction errors, where outcomes are unexpected. These may be conceptualized as four broad classes of error, including unexpected aversive events, aversive events that were expected but absent, weak learning, and context shifts.