Updated Project Summary: There is a fundamental gap in understanding how the brain produces social communication signals. Facial expressions are a vital social signal in societies, communicating internal affective state and valence of external stimuli. The continued existence of this gap is an important problem because until it is filled, it will be impossible to understand the neural principles that allow us to express emotions, exchange social information, and communicate with peers. Past work has been critically limited to properties of few cells in a single brain region. The recent discovery of the functional network for social communication signal production, when paired with multichannel electrode arrays, allows for simultaneous recordings from populations of cells which compose this distributed network. The long-term goal is to understand how the brain produces socially communicative acts. The overall objective is to elucidate how neural populations in discrete cortical areas control socially communicative facial movements. The central hypothesis is communicative facial movements are controlled by the coordinated activity of a set of functionally specific cortical regions, each containing cells with characteristic spatiotemporal receptive fields. The rationale is this proposal will determine the mechanisms of facial expression production from the level of single cells to cortical territories, enabling mechanistic study of socioemotional expression and its deficit. The hypothesis will be tested by pursuing three specific aims: 1) determine single-cell contributions to facial movement in different nodes of facial expression production network, 2) determine the functional specificity of different nodes of the facial expression production network, and 3) determine whether or not facial expressions result from discrete cortical states. Under the first and third aims, multichannel electrode arrays targeted to fMRI-localized regions will measure the simultaneous activity of neurons across multiple regions of the facial expression production network during socially communicative behavior. In Aim 2, the applicant will use these arrays to deliver intracortical microstimulation in order to causally determine each region’s functional specificity. The proposed research is innovative as it combines two cutting-edge neurophysiological methods in a novel model system of social communication to generate the first mechanistic descriptions of the cortical control of facial expressions. This research is significant because it 1) produces a mechanistic understanding from the level of single cells to a cortical network, of how the brain produces social communication signals through the face, and 2) forms a new model system in which hypotheses related to socioemotional expression and its deficit can be rigorously tested. The applicant’s career goal is to be an academic physician-scientist with a research program aimed at bringing the theoretical motivations and...