Emotions color our lives and profoundly shape the way we think and behave. Research in my lab aims to understand how emotional and social behaviors are encoded in the brain, with a main focus on the neural circuitry underlying depression and social dominance. Specifically we are looking into three major problems: First, we study how the brain represents emotions of different valence. Through simultaneously mapping the neural activity response to rewarding and aversive stimuli in the same mouse brain and at single cell resolution, we have identified a functional valence map. Second, we search for the molecular and circuit mechanism of depression, focusing on a brain region called habenula, which encodes negative reward. We have identified several key habenula-expressing molecules that play important roles in the etiology of depression. Third, we establish animal models for studying social hierarchy in mice and explore the neural mechanism underlying the dominance trait. We are recording and manipulating neural activity during social competition to study how dominance hierarchy arises from interplay between the activity of specific neural circuits and social experience such as history of winning or losing. We are tackling these problems using combinatorial cutting-edge techniques including imaging, electrophysiology (both in vitro and in vivo), molecular genetics and optogenetic. We hope that these studies will shed new light on the neural basis of some essential emotional and social behaviors, and provide therapeutic implications for the treatment of emotional disorders.