Social grouping offers social animals unique advantages to survive and social disconnection can cause negative mental and physical results that motivate animal to re-engage in group. But how social motivation is encoded and regulated in neural circuit remains unclear. In my proposed project, I will identify the brain regions and cell types that are activated during social isolation and re-grouping. Utilizing cell-type targeted calcium imaging, I will monitor the neuronal dynamics during distinct social motivation states and specific social behavioral events. To further investigate underlying circuit-level mechanisms, I will examine the synaptic connections between regions associated with isolation and grouping, and how synaptic strength changes during social isolation. Finally, cell-type and projection specific optogenetic manipulations will be conducted to regulate social motivation and alter the relevant social behaviors. This project will shed new light into the regulation of social motivation both at the cell-type and circuit-levels.