Although much is known about the anatomy and physiology of the primary sensory systems, much remains to be learned about the higher levels of processing underlying multimodal sensory integration. The goal of this project is to investigate these integrative processes as they relate to bow the human brain uses visual and eye position information to determine the location of objects in space. I propose to carry out electrical stimulation and intracranial evoked response studies in 30-40 patients who have had intracranial electrodes placed as part of the presurgical evaluation for medically intractable epilepsy. Specifically, I shall make a quantitative, systematic study of the effect of eye position on both the perceived location of the positive visual phenomena (phosphenes) induced by direct electrical stimulation of various cortical regions in humans and intracranially recorded visual evoked responses. The hypothesis that certain cortical regions represent visual information purely in a coordinate system that moves with the eyes (oculocentric) and others represent this information in a coordinate system defined by the position of the head (head-centered) will be tested and the anatomic locus of these regions will be defined. The effect of eye position on the target location errors that occur during electrical stimulation will elucidate the visual maps used by cortical regions from which phosphenes are not elicited. Advanced signal processing techniques will be employed to investigate the functional connections between the cortical areas studied. The knowledge obtained from this project will enhance our understanding of multimodal sensory integration in the brain. It will be of fundamental clinical importance in understanding and treating patients with visual neglect syndromes. In addition, the novel methods for quantitatively interpreting electrical stimulation studies and intracranial evoked responses developed as a result of this project will be of value in investigating other aspects of human neurophysiology.
