Responses in extraocular muscles from magnetic stimulation of the cat brain
Mimura, O.; Wanaka, Y.; Iwasaki, Y.; Ikeda, N.; Takubo, K.; Shimo-oku, M.
Nippon Ganka Gakkai Zasshi 94(9): 786-791
1990
ISSN/ISBN: 0029-0203 PMID: 2248163 Document Number: 357515
In 12 adult cats, pulsed magnetic stimuli were applied to the scalp, with the center of the stimulating coil over the interparietal bone. Recordings were obtained from the superior rectus, lateral rectus and inferior oblique muscles with concentric needle electrodes. In all cats, single muscle action potentials were recorded easily in all the muscles examined with latencies of 3.2 .apprx. 37.5ms (mean 15.6ms). These reponses disappeared after intravenous administration of pancuronium bromide. Furthermore, the elicited action potentials in the inferior oblique muscles disappeared by amputation of the inferior oblique branch of the oculomotor nerve. In some motor units, stronger stimuli shortened the latency of the responses. In most units, however, stimulus intensity did not influence the latency of responses over a wide range. The mean latency (15.6ms) is coincident with the latency of cortical spike potentials preceding voluntary saccades. This remarkable coincidence suggests that our pulsed magnetic stimuli have a very strong possibility of generation of human saccades. Thus, magnetic stimulation of the scalp may provide further information relevant to the normal operation of the oculomotor system.