Corticovestibular interactions: anatomy, electrophysiology, and functional considerations.

This review summarizes anatomical and electrophysiological observations related to corticovestibular interactions as a step toward understanding their possible functions. Vestibular information is represented in at least three distinct regions of the cerebral cortex in cats and monkeys: the parietal and somatosensory cortex and the parietoinsular vestibular cortex. In addition, vestibular-related signals are found in more extensive regions, including the motor and premotor regions and frontal eye fields. Most of these regions also project directly to the vestibular nuclei. In monkeys, at least six cortical regions have been identified, including the motor, somatosensory, parietal and temporal areas. Most of these regions receive vestibular projections via the thalamus. Most neurons in those cortical areas respond to head velocity and receive converging vestibular, visual and somatosensory input. Electrical stimulation of some of these cortical areas in anesthetized cats influences the activity of many vestibular nuclear neurons including those projecting to the spinal cord. Lesions of the parietal vestibular regions impair the vestibulo-ocular reflex (VOR) and visual suppression of the VOR as well as vestibular-related cognitive functions such as spatial perception and memory in human subjects. Diffuse cortical damage also results in similar impairment of the VOR and suppression of the VOR and possibly the vestibulo-collic reflex. Such impairments after cortical lesions may well be due in part to interruption of cortico-vestibular connections. Future studies in alert animals should focus on the role of different cortical regions projecting to the vestibular nuclei, specifically on how each affects the processing of vestibular signals that mediate vestibulo-motor reflexes and that are used for vestibular related cognitive processes.