Neural circuit mechanisms for experience-dependent observational fear

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PROJECT SUMMARY The ability to vicariously experience the other's aversive feelings in a situation, a process called observational fear (OF), is critical to live in society. Malfunctions of OF represent well-described findings in individuals with autism spectrum disorders. In OF, an observer witnesses a demonstrator in an aversive situation and responds with fear behaviors. If the demonstrator's reaction is robust, the observer easily expresses OF without prior similar experience and social familiarity with demonstrator (we refer to as innate OF). However, in nature and our lives, the demonstrator's reaction is often ambiguous and thus difficult for the observer to understand. To fully understand the other's situation, the observer utilizes both prior similar own experience and social familiarity that facilitate OF (we refer to as experience-dependent OF; Exp OF). While innate OF primarily depends on the anterior cingulate cortex (ACC) and basolateral amygdala (BLA), the neural mechanisms of Exp OF remain unexplored. My goal is to elucidate the neural mechanisms of how both prior similar own experience and social familiarity enable the observer to fully understand the other's aversive situation from their ambiguous reaction, by examining hippocampal (HPC)-BLA neural circuits in a mouse OF model that delivers strong electrical shocks to the demonstrator eliciting a robust reaction or weak electrical shocks eliciting an ambiguous reaction. Recently, our preliminary studies showed that ACC is dispensable for Exp OF, while ACC is essential for innate OF. On the other hand, both dorsal HPC (dHPC) and ventral HPC (vHPC) are crucial for Exp OF, but not for innate OF. BLA is required for both Exp and innate OF. These findings lead us to propose distinct neural circuits in Exp and innate OF. The central hypothesis of this model is that the dorsoventral HPC to BLA pathways generate and reactivate a neural ensemble of BLA neurons encoding prior similar own fear Guided by strong preliminary data, first, we propose that the dorsoventral HPC to BLA pathways are crucial for Exp OF, while the ACC to BLA pathway is essential for innate OF. Second, we propose that the reactivation of a neural ensemble of BLA neurons encoding prior similar own fear experience (a fear memory ensemble) mediates Exp OF as the perception-action mechanisms. Third, we propose that the pathway from dHPC to BLA generates the fear memory ensemble in BLA during own fear experience and then vHPC neurons respond to the familiar demonstrator's fearful situation to reactivate the fear memory ensemble in BLA to elicit Exp OF. experience, which facilitates Exp OF, while ACC induces robust BLA activity for innate OF. Collectively, our proposed research will broadly impact the field of learning and memory by characterizing neural circuits and their neural process about how we understand the other's aversive situational experience. Potentially, the neural mechanisms can be generalized for other types of empathy to vicariously experience the other's feeling/situation.