P 14. A detailed evaluation of surround inhibition in human motor cortex using transcranial magnetic stimulation

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• 作者：N. Thirugnanasamb ; am ; R. Khera ; H. Wang ; S. Kukke ; M. Hallett
• 刊名：Clinical Neurophysiology
• 出版年：2013
• 出版时间：October, 2013
• 年：2013
• 卷：124
• 期：10
• 页码：e71
• 全文大小：37 K

文摘

Surround inhibition (SI) is a feature of motor control for which the physiology is still unknown . This phenomenon is impaired in patients with focal hand dystonia and hence it becomes relevant to study it more in detail. Several studies have demonstrated SI in the human motor system using transcranial magnetic stimulation (TMS) . In all these studies SI was measured by applying a single suprathreshold TMS pulse during the movement initiation phase. The figure of eight coil was positioned such that it induced current along the postero-anterior direction in the brain.

We were interested to study SI not just at a single intensity, but at intensities ranging from sub-threshold to supra-threshold levels. Also, we wanted to explore if SI could be elicited when the motor cortex was stimulated along other directions (antero-posterior, latero-medial).

10 healthy volunteers participated in the study. Their task was to perform a brief isometric index finger flexion on hearing a tone. EMG was recorded from the first dorsal interosseous (active muscle) and the abductor pollicis brevis (surround muscle). Single pulse TMS was applied at intensities ranging from 20 % to 100 % of maximum stimulator output at 5 % intervals either before the tone (rest) or after the tone ¡«75 ms before expected onset of muscle activity (SI). The MEP amplitudes were then plotted against stimulation intensities to obtain the MEP recruitment curves for the rest and SI conditions separately. The recruitment curves were plotted with the coil held in three directions (P-A, A-P, L-M) for every subject.

We found that SI can be elicited when the coil was positioned in the P-A direction and only within a certain range of supra-threshold intensities. Maximum SI was seen around 150 % MT. Stimulating the motor cortex along the A-P direction did not elicit SI, rather showed facilitation that peaked at around 120 % MT. We can therefore conclude that SI can be elicited in those neuronal groups that can be stimulated best along the PA direction.