The purpose of this protocol is to investigate the changes in interhemispheric inhibition (IHI) between human motor cortices with learning of performance of an accurate motor task (pinch force control). Performing a simple motor task is associated with activation in the contralateral motor areas. Activation of the ipsilateral motor/premotor cortex might be elicited by performing more challenging and difficult unimanual motor tasks. However, the functional role played by this ipsilateral activation has been controversial, and is felt to be more prominent with more complex tasks. Several studies using paired-pulse transcranial magnetic stimulation (TMS) revealed a significant IHI from the active upon the non-active hemisphere. Together these results suggested IHI between motor cortical areas may play a critical role in motor control and could influence manual dexterity. Taking these into account, it raises the interesting question of whether the IHI balance between both motor cortices is progressively modified during the learning phase of an accurate motor task. We hypothesize that learning to perform a tracking motor task requiring accurate control of pinch force generation (Tracking accurate), will increase IHI from the "learning" to the "non-learning" hemisphere to a larger extent than learning to perform a less precise tracking motor task (Tracking non-accurate). The primary outcome measure will be the amount of changes in IHI from the "learning" to the "non-learning" hemisphere as a function of learning both motor tasks.
- INCLUSION CRITERIA Healthy volunteers will be eligible for the study if they are: - are between the ages of 18-40 years; - are right-handed; - are able to perform tasks required by the study; - are willing and able to give consent EXCLUSION CRITERIA Healthy volunteers will not be eligible for the study if they: - are unable to perform the tasks; - are left-handed; - have a history of neurological and psychiatric illness, or of alcohol or drug abuse or severe language disturbances or serious cognitive deficits; - have uncontrolled medical problems, such as heart, lung or kidney disease, epilepsy or diabetes mellitus, have severe tactile deficits (defined by Frey filaments exerting a force of 4 N to the distal pad of the finger); - have a cardiac pacemaker, intracardiac lines, implanted medication pumps, neural stimulators, metal in the cranium, with the exception of dental braces.