Adaptive behavior in social contexts depends on the ability to encode, retain, and use information about other individuals. Studies in rodents have highlighted the ventral hippocampus as a key substrate for storing social memories, yet the mechanisms that coordinate neuronal ensemble dynamics remain poorly understood. Using large-scale extracellular recordings with high-density silicon probes, we found that neurons responsive to familiar conspecifics were preferentially reactivated during sharp wave-ripples (SPW-Rs) following social interaction. In Shank3 knockout mice, the proportion of social memory neurons was reduced and the amplitude of SPW-Rs was diminished. We further identified two distinct subpopulations among social memory neurons: one encoded social identity through nonlinear responses to specific combinations of sex and strain, whereas another selectively encoded sex or strain as generalized social properties. These cell types also exhibited distinct temporal coding with respect to hippocampal theta phase. Genetic ablation of the upstream dorsal CA2 region (dCA2) reduced the fraction of neurons with nonlinear responses, including those encoding social identity, and impaired nonlinear population coding of familiar conspecifics.

  The latter part of the talk will focus on my previous work on adaptive decision making, including electrophysiological recordings from midbrain dopamine neurons and cortical neurons in head-fixed mice performing a probabilistic reversal learning task. This work has motivated my broader interest in how offline processing and circuit dynamics across the hippocampus, amygdala, and related brain regions contribute to adaptive behavior.