Abstract
Publisher Summary This chapter discusses the time course of motor excitability in relation to a task related movement, using subthreshold transcranial magnetic stimulation (TMS) to the motor cortex contralateral and ipsilateral to the movement. Motor cortex excitability is influenced by multiple inputs that may vary, depending on the task, preparation for voluntary movement, and sensory input. The task related movement was associated with a marked increase in the contralateral motor excitability. The time course of pre-movement motor excitability includes two excitatory phases, the first beginning about 500 ms before movement, separated by a short premovement inhibitory period (between 150 and 200 ms), from the second prominent phase, which peaked with the movement. Postmovement excitability gradually declined, but was still significantly elevated up to 600 ms after the movement. Excitability of the motor cortex ipsilateral to the movement was suppressed immediately, following the movement up to 1 s thereafter. The reasons underlying these discrepancies may relate to the methodology employed. Electroen-cephalography (ECG), magnetoencephalography (MEG), and evoked potentials reflect the summated activity in numerous brain regions. In contrast, transcranial magnetic stimulation (TMS) measures excitability in a more restricted region of the brain.
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