Intra- and intersubject reliability of abductor pollicis brevis muscle motor map characteristics with transcranial magnetic stimulation.

Abstract

To determine consistency in motor maps of the abductor pollicis brevis (APB) muscle using transcranial magnetic stimulation (TMS) with conventional and close-spaced surface electrode recording placements. Nonrandom convenience sample. TMS laboratory. Eleven participants without any known neurologic disorders. The left hemisphere of right-hand-dominant subjects was mapped using TMS at each of 2 sessions, separated by 1 to 8 weeks. Measurements at each session included the resting motor threshold, active site locations and average motor response amplitude for active sites, normalized map volume, and center of gravity (COG) for both electrode array configurations. The normalized map volume was larger for the conventional electrode placement than for the close electrode placement (4.23 cm2 vs 3.44 cm2, P=.010). Resting motor threshold was higher for the close-spaced than for the conventional-spaced electrodes (48.36% vs 46.59%, P=.028). No statistical difference was found between sessions and within electrode placements for the normalized map volume, for resting motor threshold, or for the mean motor amplitude of the most active site for each map. No statistical difference was observed for the COG distance between electrode placements. This study revealed differences between close-spaced and conventional-spaced surface electrode placement for TMS motor map volumes and for resting motor thresholds. The motor maps for the APB muscle were reliably reproducible between sessions for each electrode array.