Project Summary In vertebrate animals, the vestibular system (primarily known as the “balance system” of the brain) interprets head-movement and orientation signals to provide organisms with a sense of self-motion. The vital contribution of vestibular system to reflexive control of posture, gaze, and gait is well characterized; however, far less is known about the neural substrates underlying higher-order vestibular functions, such as the perception of self- motion and the awareness of one's orientation in space. These functions rely on the cortical integration of vestibular input with somatosensory and visual input. In non-human primates, the parieto-insular vestibular cortex (PIVC) is uniquely suited to perform this multisensory integration. Unlike other vestibular-sensitive cortical areas, PIVC has direct access to vestibular, somatosensory, and visual input from the thalamus; indeed, it is hypothesized that other vestibular cortical areas receive their vestibular input from PIVC, thus making it a nexus for higher-order vestibular function. Despite its hypothesized importance, extremely little is known about the neural mechanisms by which PIVC integrates vestibular and extra-vestibular input, and whether this integration is context dependent. For example, it is unclear whether PIVC neurons differentiate between vestibular input generated during passive vs. active movements; such differentiation is seen in the vestibular nuclei and thalamus and is thought to be essential for producing a sense of motor agency. To investigate these issues, I propose to conduct high-density neurophysiological recordings in behaving primates during both passive stimulation and actively generated head and whole-body movement. In Aim 1, I will investigate how PIVC integrates passively applied vestibular and somatosensory input (Aim 1.1) and then vestibular and visual input (Aim 1.2). In Aim 2, I will investigate whether PIVC differentially processes vestibular input during passive and active movement. Specifically, I will examine how PIVC processes vestibular input generated during natural self-motion (i.e., self- motion relying on sensorimotor input in the form of a head-turning task, Aim 2.1). I will then examine how PIVC processes vestibular input generated during a learned, cognitively demanding motor task (Aim 2.2). In both aims, I will determine how individual neurons in PIVC encode vestibular and extra-vestibular input, as well as how this information is represented at the population level. The proposed experiments will resolve two questions which are fundamental to understanding PIVC function: 1) How does PIVC integrate multisensory input to construct a percept of self-motion? and 2) Is the processing of self-motion by PIVC neurons consistent with that required to provide a sense of motor agency? Furthermore, the proposed experiments will determine how sensorimotor and cognitive percepts of self-motion are represented in PIVC. This research will provide new i...