Figure 7.

PET Non‐responders. The M1 response to voluntary finger tapping (left) and the absence of an M1 response to TMS (right) are shown in group‐mean SPIs formed from four subjects in whom a significant M1was not observed with per‐subject PET image analysis. Although the response to hand movement rose with averaging to a Z‐score of 4.0 (average of per‐subject Z‐scores = 3.4), no response to TMS was observed even with averaging. As TMS did produce corticospinal track excitation (as evidenced by TMS‐induced muscle contractions), we infer that the EMG was induced via direct axonal depolarization rather than via cortical excitation.