Gaze following and facial mimicry are fundamental elements of social behavior in both humans and non-human primates. Gaze following is critical for the development of shared attention and for a mental phenomenon called theory of mind. Facial mimicry is a form of shared emotion and constitutes the basis of empathy. These behaviors are profoundly affected in neurodevelopmental disorders and in severe mental illness, including schizophrenia, depression, and social phobia. When the amygdala is damaged or is functioning abnormally gaze following and facial mimicry are also impaired, suggesting that the amygdala may play an important role in these behaviors. To determine the role of the amygdala in these basic social behaviors, we propose to inactivate the amygdala of monkeys while they "interact" with naturalistic videos that elicit gaze following and facial mimicry. The amygala, however, comprises several nuclei, each with a different connectivity and different functions. We propose to inactivate selectively each main nucleus of the amygdala to test the following hypotheses: (1) the basolateral nuclei of the primate amygdala are necessary for gaze following, and (2) the central nuclei are necessary for facial mimicry. These hypotheses are based on the known anatomical connectivity of each nuclear group with cortical and subcortical structures involved in social behavior. The basolateral nuclei are connected to cortical areas involved the control of eye movements and in higher cognitive functions that might be necessary to determine where individuals are looking. The central nuclei are connected to subcortical circuits that serve low- level perceptual and motor functions that might be necessary to make eye contact and to imitate involuntarily facial expression. The proposed research will determine the role (s) of different amygdala nuclei in the elaboration of basic social behaviors. This will complement our current understanding of the role of the amygdala in social perception. A more detailed understanding of the role that individual nuclei of the amygdala play in the production of gaze following and facial mimicry will take us one step closer toward identifying the causes of shared social deficits in neurodevelopmental and other psychiatric disorders.
The current proposal is relevant to mental health because it explores the possible source of shared deficits of social behavior in neurodevelopmental disorders and in several mental illnesses. Gaze following and facial mimicry are basic behaviors on which more complex social behaviors are built and they are impaired in multiple mental disorders. The proposed research will determine any causal relationship between the functional integrity of amygdala and production of these basic social behaviors in non-human primates.