 The neurobiological mechanisms by which binge alcohol consumption disrupts social and emotional functioning are unknown. Here, the authors demonstrate that sex-specific social and arousal disturbances induced by binge alcohol consumption are driven by dysregulation of serotonergic signalling and activation of five HT2C receptor-containing neurons in the lateral herbenula in mice. This article was authored by M. E. Flanagan, O. J. Hahn, S. D. Ambrosio, and others.