**Faculty Candidate Search - Systems Neuroscience**

Top-down prefrontal inputs to hippocampus have been hypothesized to be important in memory consolidation, retrieval, and the pathophysiology of major psychiatric diseases; however, no such direct projections have been described. I will discuss the recent discovery of such a monosynaptic prefrontal (predominantly anterior cingulate) to hippocampus (CA3/CA1) projection in mice. Optogenetic manipulation of this projection (here termed AC-CA) determined that activity in AC-CA is both necessary and sufficient for memory retrieval. To explore the network mechanisms of this retrieval process, we developed and applied tools to observe cellular-resolution neural activity in CA3 while stimulating AC-CA projections during memory retrieval in mice behaving in virtual-reality environments. Using this approach, we found that learning drives the emergence of sparse set of hub neurons in CA3, whose activity is highly correlated with the local network and capable of recruiting population-wide synchronous events; These neurons are then preferentially recruited by the AC-CA projection during memory retrieval. These findings provide one of the first reports of a top-down memory retrieval circuit in the brain, and more broadly, reveal a hub-dependent retrieval mechanism that has implications for the patterning and storage of salient memory representations.