Social behavior in mice following chronic optogenetic stimulation of hippocampal engrams.

The hippocampus processes both spatial-temporal information and emotionally salient experiences. To test the functional properties of discrete sets of cells in the dorsal dentate gyrus (dDG), we examined whether chronic optogenetic reactivation of these ensembles was sufficient to modulate social behaviors in mice. We found that chronic reactivation of discrete dDG cell populations in male mice largely did not affect social behaviors in an experience-dependent manner. However, we found that social behavior in a female exposure task was increased following chronic optogenetic stimulation when compared to pre-stimulation levels, suggesting that the protocol led to increased social behavior, although alternative explanations are discussed. Furthermore, multi-region analysis of neural activity did not yield detectable differences in immediate-early gene expression or neurogenesis following chronic optogenetic stimulation. Together, these results suggest that the effects of chronic optogenetic stimulation in the dDG on social behaviors are independent of the contextual experience processed by each cellular ensemble.