MEPs elicited by rotational-field multi-directional dual-H-coil TMS show marked differences compared to MEPs elicited by uni-directional figure-of-8 and H7 coils

Uni-directional transcranial magnetic stimulation (udTMS; e.g., via figure-of-8 coil) depolarizes mainly neurons whose axonal orientation aligns with the direction of the induced electric field. A novel dual H-coil (T360°Coil Array) TMS system (Brainsway TM , Israel) generates a rotational magnetic field aimed to recruit a larger neuronal population by induction of a multidirectional electric field (rfTMS). The purpose of this study was to assess comparatively neurophysiological properties of motor evoked potentials (MEPs) elicited from the first-dorsal interosseous (FDI) muscle following udTMS (via figure-of-8 and H7 coils) vs. multidirectional rfTMS. In this study, 10 healthy adult subjects received TMS via the three coil configurations in random order. The results showed that rfTMS elicited larger MEPs at a lower resting motor threshold (rMT) compared to the uni-directional coils. These findings suggest that rfTMS is likely to recruit larger populations of neurons compared to conventional udTMS coil configurations. This may bear advantages in efforts to enhance motor recovery following brain damage by treatments using TMS.