Cerebral cortex lesions, at the junction of the posterior parietal and superior temporal areas, cause an incapacitating syndrome of visuospatial disorientation (Holmes, 1918). The fact that visual, vestibular, or somatosensory pathology may also disrupt spatial orientation suggests that these mechanisms are integrated into a multisensory percept of extrapersonal space, possibly within parietotemporal cortex. During self-movement, visual motion processing interacts with vestibular and somatosensory mechanisms to support spatial orientation. I propose to test whether parietotemporal neurons might contribute to those interactions by recording neuronal responses to visual and non-visual motion stimuli. The activity of single neurons in parietotemporal areas MSTd and 7A of awake monkeys will be recorded during visual motion simulations of the self-movement scene, during vestibular and somatosensory activation by passive linear movement. Three sets of experiments are planned to examine critical issues regarding neuronal responses and self-movement perception. First, I will compare the relative selectivity of these neurons for the patterned visual motion seen during observer movement (optic flow) and visual figure motion, which can result from observer or object movement. Second, I will record the responses of these neurons to linear self-movement in the dark and determine what contributions vestibular and somatosensory mechanisms might make to those responses. Third, I will combine visual motion with linear self-movement to define the dynamics of multisensory interactions in these neurons. These studies will test the capacity of MSTd and 7A neurons to integrate visual, vestibular and somatosensory information during self-movement. My goal is to characterize their potential contributions to spatial vision, locomotor, and oculomotor control. The results will be relevant to understanding central mechanisms which serve fundamental behavioral capacities such as the stabilization of gain and gaze, and the maintenance of spatial orientation. In addition, the results will provide a basic understanding of how spatial vision might interact with the vestibular and somatosensory systems to maintain postural control in health, disease, and aging.
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