REPRESENTATION OF CORTICAL MOTOR FUNCTION AS REVEALED BY STEREOTACTICTRANSCRANIAL MAGNETIC STIMULATION

Cortical motor representation of 12 muscles of the trunk and the upper and lower extremity was investigated in 18 healthy subjects using foc al transcranial magnetic stimulation (TMS) in conjunction with a frame less stereotactic system (FSS). This combination allowed us to orienta te stimulation sites to the individual central sulcus rather than to b ony landmarks. Distinct but overlapping areas of muscle representation were identified and the 3-dimensional representation of those 12 musc les along the course of the central sulcus was obtained. With increasi ng stimulus intensity, the cortical output maps changed in that more m uscles became excitable, motor evoked potential (MEP) amplitude and si ze of the responsive area increased and latency of the MEP decreased. These effects were more pronounced for proximal than for distal muscle s, indicating a more widespread organization of corticospinal motor pr ojection related to proximal muscles. The combination of TMS and FSS r epresents a method with which functional information can be directly r elated to underlying cortical anatomy. This correlation will be useful in the assessment of higher brain functions with TMS. (C) 1998 Elsevi er Science Ireland Ltd.