One of the general aims of this research is to show how the cerebral cortex controls the flow of afferent information selectively to direct purposeful movements of the hand. Prehensile movements of the hand use cutaneous feedback to adjust grip forces to the weight and friction of a handled object to minimize slip on the skin. By contrast, in manual exploration, the movements are organized to facilitate slip over the finger tips to acquire the tactile information necessary to achieve a perceptual objective such as object recognition. Because of the fundamentally different relationship of somatosensory input to motor output during prehension as opposed to exploratory movements, the same input afferents signaling normal and tangential forces on the skin may have different effects on the motor cortex under these two contrasting behavioral conditions. There are three specific aims associated with this proposal. The first is to show that during exploratory hand movements, the somatosensory cortex acts as a salient feature amplifier and filter used to extract particular stimulus characteristics encountered during active tactile exploration. The second objective is to show that the same stimulus features are somatotopically preserved and can be found in the neuronal discharge patterns of motor cortical cells receiving input relayed through the somatosensory cortex and controlling the muscles involved in exploratory hand movements. The third objective is to show that reversible inactivation of the somatosensory cortex produces deficits in exploratory movements guided by touch sensation and that these behavioral deficits are accompanied by a demonstrable loss or significant alteration in the cutaneous receptive fields of hand area neurons recorded in the motor cortex. This research has given rise to a close collaboration with Dr. Roger Madison of the Neurosurgery Division at Duke University Medical Center who is currently using our grasp and hold task and apparatus to develop and evaluate novel techniques for the neurosurgical repair of peripheral nerve injuries to the hand. The addition of tactile exploration task would be a particularly useful adjunct to this research application. Ultimately both the prehension and tactile exploration tasks have promise as diagnostic and therapeutic techniques to aid in rehabilitation medicine with stroke patients and patients with peripheral neuropathies.