Selective magnetic stimulation of cervical nerve roots with a figure-eight coil

We investigated the possibility of selective stimulation of cervical nerve roots in healthy subjects. The skin surface on the anterior neck was divided into 12 portions of 2 cm×2 cm each. Each portion was stimulated magnetically with a figure-eight coil. Induced eddy currents were downward. M-waves of the infraspinatus, the deltoid, the biceps brachii, the triceps brachii, the extensor digitorum communis, the flexor carpi ulnaris, the abductor pollicis brevis, and the abductor digiti minimi were monitored. The stimulation of some specific portions evoked M-waves of only the infraspinatus and the deltoid. The infraspinatus and the deltoid are innervated predominantly by the 5th cervical nerve, so these results suggest that the 5th cervical nerve root was selectively stimulated with a figure-eight coil