The objective of this research is to gain a better understanding of the brain mechanisms underlying sensory-motor adaptation. Humans display a remarkable ability to adapt to a new situation, especially when available sensory information conflicts. Behaviorally, this adaptive ability has been well described. One way researchers have investigated this adaptation is by having subjects attempt to manually point at a visual target while wearing prism goggles. Initial reaching attempts are inaccurate because the prism systematically bends the light before it enters the eyes such that the target appears to shift left or right of its actual location. However, with repeated trials, the subject is able to adapt to the altered visual input and generate accurate responses. When the goggles are removed there is an aftereffect in which the reaching responses are inaccurate in the opposite direction to that observed during the prism exposure period. Based on these behavioral characteristics of prism adaptation, recent neurophysiological, clinical and human brain imaging studies have begun to identify the network of brain sites that contribute to this simple form of learning, but a more complete understanding of the potentially different contributions of the network's components is required. This goal will be accomplished by examining the degree to which adaptation is disrupted in normal, healthy human subjects when transcranial magnetic stimulation (TMS) is applied over the cerebellum, posterior parietal cortex, or premotor cortex during the training period. It is predicted that TMS delivered over each of these sites will have different effects on the degree of adaptation that occurs depending upon when the stimulation is given and the availability of visual feedback from the hand. In addition to expanding our basic understanding of the nature of sensorimotor adaptation and its underlying mechanisms, the proposed research may also be useful in contributing to the design of motor rehabilitation therapies.
