Mechanisms of interhemispheric inhibitionin human motor cortex

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Promoting neural plasticity within motor cortex is a key research focus in human neuroscience. This scientific interest is largely driven by the desire to understand how the brain and spinal cord control movement and to ultimately inform the development of therapeutic approaches. Within the motor cortex there are representations of muscles, and the space or territory occupied by these representations change depending on the context of the task. For example, when movement occurs, representations expand. However, little is known about the mechanisms that govern changes in the muscle representations within human motor cortex. One mechanism likely to contribute is called interhemispheric inhibition. This is a neural mechanism whereby the motor cortex in one hemisphere inhibits the activity of the motor cortex in the opposite hemisphere. Our previous research has shown that the strength of interhemispheric inhibition relates to the size of the muscle representation within motor cortex. This is an important finding because, if interhemispheric inhibition governs some properties of motor cortex organization, we may be able to manipulate interhemispheric inhibition as a method to alter the organization within motor cortex. To accurately and effectively utilize interhemispheric inhibition the proposed program addresses these questions: 1) What neurotransmitter receptors mediate interhemispheric inhibition? 2) Does the magnitude of interhemispheric inhibition relate to the size of the muscle representation within motor cortex? 3) Can interhemispheric inhibition be manipulated to create concomitant changes in the muscle representations within motor cortex? Focused on the primary motor cortex in humans, the proposed program will characterize a neural mechanism that is predicted to govern activity in motor cortex. The program will uniquely combine methodologies of neurophysiology, pharmacology, functional near-infrared spectroscopy, and one-proton magnetic resonance spectroscopy (1H-MRS) to address fundamental questions in human motor cortex. This ground-breaking research will make unprecedented strides in basic neuroscience by 1) identifying the inhibitory neurotransmitter receptors that mediate interhemispheric inhibition, 2) identifying new opportunities to modulate interhemispheric inhibition, and 3) identifying new opportunities to modify the organization of human motor cortex.