• W P Teo, J P Rodrigues, F L Mastaglia, and G W Thickbroom.
• Australian Neuro-Muscular Research Institute, Centre for Neuromuscular and Neurological Disorders, M518, University of Western Australia, Nedlands, WA 6009, Australia.
• Exp Brain Res. 2012 Jan 1; 216 (1): 41-9.

AbstractTranscranial magnetic stimulation has been used to study changes in central excitability associated with motor tasks. Recently, we reported that a finger flexion-extension task performed at a maximal voluntary rate (MVR) could not be sustained and that this was not due to muscle fatigue, but was more likely a breakdown in central motor control. To determine the central changes that accompany this type of movement task, we tracked motor-evoked potential (MEP) amplitude from the first dorsal interosseous (FDI) and abductor pollicis brevis (APB) muscles of the dominant hand in normal subjects for 20 min after a 10 sec index finger flexion-extension task performed at MVR and at a moderate sustainable rate (MSR) and half the MSR (MSR(/2)). The FDI MEP amplitude was reduced for up to 6-8 min after each of the tasks but there was a greater and longer-lasting reduction after the MSR and MSR(/2) tasks compared to the MVR task. There was a similar reduction in the amplitude of the FDI MEP after a 10 sec cyclic index finger abduction-adduction task when the FDI was acting as the prime mover. The amplitude of the MEP recorded from the inactive APB was also reduced after the flexion-extension tasks, but to a lesser degree and for a shorter duration. Measurements of short-interval cortical inhibition revealed an increase in inhibition after all of the finger flexion-extension tasks, with the MSR task being associated with the greatest degree of inhibition. These findings indicate that a demanding MVR finger movement task is followed by a period of reduced corticomotor excitability and increased intracortical inhibition. However, these changes also occur with and are greater with slower rates of movement and are not specific for motor demand, but may be indicative of adaptive changes in the central motor pathway after a period of repetitive movement.

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