UC San Diego

Regulation of social connection is highly evolutionarily conserved and critical for the survival and success of a species, yet the mechanisms that regulate this vital social need state are not fully understood. This thesis aims to address some of the many unanswered questions in this field, including: How do neural circuits and systems generate an emotional state (such as a loneliness-like state) at behaviorally relevant timescales? What are the neural and behavioral adaptations that occur following different phases of social isolation? How do factors, such as social rank and sex, affect the neural control and expression of loneliness-like behaviors? Chapter 1 of this dissertation introduces my working framework of social homeostasis—the adaptive function that allows individuals to maintain social connection at an optimal level. Chapter 2 of this dissertation characterizes an often-overlooked brain region—the Amygdalostriatal transition zone—as a biological substrate that allows for the representation of valence at a behavioral timescale, an arguably missing piece in the canonical emotional processing amygdalar neural circuitry. Chapter 3 examines three dorsal raphe nucleus (DRN) dopaminergic circuits that represents different facets of a loneliness-like state—namely prosociality and aversion. Finally, Chapter 4 uncovers the sex-specific and time-dependent effects of social isolation, as well as a potential role of the medial prefrontal cortex in the integration of social context with an individual’s social environment.