Task-dependent modulation of excitatory and inhibitory functions within the human primary motor cortex

• DOI: 10.1007/s00221-003-1448-y
• Publication Date: 2016-10-17T22:14:40Z
• Authors: Michele Tinazzi; Simona Farina; Stefano Tamburin; Stefano Facchini; Antonio Fiaschi; Domenico Restivo; Alfredo Berardelli
• Keywords: Adult; Male; 0301 basic medicine; Analysis of Variance; magnetic stimulation; motor control; motor cortex; sensorimotor interaction; task dependence; Motor Cortex; Neural Inhibition; Evoked Potentials, Motor; 03 medical and health sciences; magnetic stimulation; motor cortex; motor control; task dependence; sensorimotor interaction; Motor Skills; Humans; Female; Electromagnetic Phenomena

We evaluated motor evoked potentials (MEPs) and duration of the cortical silent period (CSP) from the right first dorsal interosseous (FDI) muscle to transcranial magnetic stimulation (TMS) of the left motor cortex in ten healthy subjects performing different manual tasks. They abducted the index finger alone, pressed a strain gauge with the thumb and index finger in a pincer grip, and squeezed a 4-cm brass cylinder with all digits in a power grip. The level of FDI EMG activity across tasks was kept constant by providing subjects with acoustic-visual feedback of their muscle activity. The TMS elicited larger amplitude FDI MEPs during pincer and power grip than during the index finger abduction task, and larger amplitude MEPs during pincer gripping than during power gripping. The CSP was shorter during pincer and power grip than during the index finger abduction task and shorter during power gripping than during pincer gripping. These results suggest excitatory and inhibitory task-dependent changes in the motor cortex. Complex manual tasks (pincer and power gripping) elicit greater motor cortical excitation than a simple task (index finger abduction) presumably because they activate multiple synergistic muscles thus facilitating corticomotoneurons. The finger abduction task probably yielded greater motor cortical inhibition than the pincer and power tasks because muscles uninvolved in the task activated the cortical inhibitory circuit. Increased cortical excitatory and inhibitory functions during precision tasks (pincer gripping) probably explain why MEPs have larger amplitudes and CSPs have longer durations during pincer gripping than during power gripping.