Project Summary Aggression is an evolutionarily conserved behavior that controls social hierarchies and protects valuable resources like mates, food, and territory. In most cases, aggression is a necessary, adaptive component of social behavior. In humans, however, some forms of aggression are considered pathological when they threaten lives, increase the risk of psychiatric impairment in victims, and incur economic burdens on society. Considerable evidence indicates that aggression is associated with aberrant facial perception in humans. Physically aggressive individuals have a tendency to identify ambiguous faces as threatening or angry. This suggests that these individuals have a perceptual bias which impairs the ability of the individual to interpret the level of threat correctly. There is ample evidence in human and non-human primates that the amygdala plays a key role in social perception. Studies with human and non-human primates examining the amygdala's role in social perception have focused on the lateral and basolateral amygdala given their extensive connections with the visual system and because they are a highly dependent on vision. Conversely, rodents are more reliant on olfaction, and thus, we need a deeper understanding of amygdala interactions with olfactory structures during social encounters. The posterior cortical amygdala (COAp) is one such region which receives input from olfactory structures. Our preliminary data suggest that activation of ESR-1 cells in the COAp are necessary for aggressive behavior to occur in males but not females. Furthermore, these cells show an increase in activity during attack behavior in males. In addition to the expected input from the main olfactory bulb, we discovered that this cell population also receives input from the ventral striatopallidal system, which is involved in motivational processes. For the K99 phase of this proposal, I will test the hypothesis that the ventral striatopallidal system affects the motivation to attack by modulating preparatory activity in the COAp. Over the R00 phase, I will build a research program to test the hypothesis that the COAp mediates state-dependent responses to social olfactory stimuli. In order to induce an “aggressive state” in mice we will use the social instigation model. The results from this proposal will increase the field's understanding of how non-sensory variables affect what are traditionally known as sensory regions. In addition, the proposed training will allow me to develop a future research program geared towards identifying mechanisms underlying the effects of altered behavioral states on perceptual processes.