Motor Potentials of Lower-Lip Mimetic Muscles and Distal Arm Muscles to Cortical Transcranial Magnetic Stimulation: The Possibility of One-Dimensional Separation of Two Cortical Representation Areas

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Abstract
The cortical representation of the abductor pollicis brevis muscle (APB) was investigated by transcranial magnetic stimulation (TMS) along the interaural line on the head surface in 17 healthy subjects. Comparing amplitudes of motor evoked potentials (MEPs) with those obtained by cortical TMS of lower-lip muscles, we found a considerable overlap between the areas from which reproducible MEPs of APB and lower-lip muscles could be elicited. However, there was a statistically significant separation of the two areas, the APB area being placed more medially. With regard to short examination procedures it can be concluded that a separation between distal arm and facial muscles is possible not only by two-dimensional cortical mapping procedures, but also by one-dimensional cortical TMS.