Discrete Circuits of the Ventral Hippocampus in Threat-Based Learning and Memory

While the hippocampus has intrigued generations of neuroscientists for its contributions to cognitive and emotional processing, functional specialization along its longitudinal axis confers particular importance to the ventral hippocampus (vHPC) in affective regulation under normal and pathological conditions. In particular, vHPC is extensively linked to the encoding, expression, and extinction of fear memories, which mediate behavioral adaptation to environmental threats. Despite decades of research, however, many questions remain about precisely what is encoded among specific populations of vHPC neurons and what brain systems cooperate in processing this information during fear regulation. Furthermore, as insights accumulate into the function of discrete afferent projections of vHPC, an important area of focus is how vHPC circuitry might be organized to support different output patterns through synaptic integration. Here, we summarize the current understanding of these issues based on contemporary circuit-based approaches and highlight potential clues to the anatomical and functional organization of synaptic networks that may help reconceptualize vHPC as a system of interacting modules.