Emotional expressions are an evolutionarily conserved form of communication and being able to recognize an emotion from a face or voice is a fundamental social function. Disturbances in emotional recognition are a common finding in many psychiatric diseases, but little is understood about the circuit processes that facilitate this behavior. Compared to neutral faces, viewing expressive faces (e.g. sad, angry, or happy faces) engages the amygdala and ventrolateral prefrontal cortex (VLPFC). Although the amygdala contains neurons that selectively respond to specific expressions, the overall activity of these neurons does not sort expressions into discrete categories. This suggests that the amygdala signals the salience of specific features but that it is not the site where categorization of these expressions occurs. In humans, the VLPFC is especially active when comparing facial expressions or matching expressions with descriptive words. In non-human primates, neurons in the VLPFC are highly responsive to faces and voices. Thus, the VLFPC may be a point where population activity categorizes expressions, but this has yet to be systematically tested. My preliminary data identifies VLPFC neurons with selective responses for expressions and a direct projection from the amygdala to the VLPFC, in the macaque. Building on these findings, this proposal seeks to combine anatomical tract-tracing, simultaneous dual-site multielectrode neurophysiology, and naturalistic, audiovisual expressions to test the hypothesis that the amygdala transmits information about the salient sensory features of emotional expressions directly to the VLPFC, where population activity segregates expressions into associated emotional categories. Using tissue from macaques with retrograde tracers placed at VLPFC sites that were highly responsive to faces and vocalizations, I will localize the origin of this projection in the amygdala and characterize it?s termination in complementary injections (Aim 1). Concurrently, I will implant multichannel electrodes into the amygdala and VLFPC to simultaneously record neuronal ensemble activity while macaques view movies of naturalistic, socio-emotional expressions i.e. facial gestures and associated vocalizations (Aim 2). By analyzing the sensory modalities that drive expression related responses, analyzing the population activity of these neurons, and comparing their response latencies between the amygdala and VLPFC, I will gain insight into the neuronal processing that occurs between these two regions to facilitate emotional recognition. In addition, learning to conduct anatomical and electrophysiological investigations into circuits for social behavior will serve as foundation for my intended a career as a translational researcher in psychiatry.
PROPOSAL NARRATIVE Facial and vocal expressions efficiently communicate inner emotional states to others, but how emotions are recognized from these expressions is far from understood. I propose to study the neural underpinnings of this process through a combination of anatomical and dual-site electrophysiological investigations between the amygdala and prefrontal cortex in macaques. These investigations will expand our understanding of the circuit mechanisms of this critical social behavior that is frequently disrupted in a variety of psychiatric disorders.
