Transcranial magnetic stimulation of the oculomotor and abducens nerves: determining the site of excitation in the cat.

The authors have attempted to stimulate the feline oculomotor and abducens nerves using a magnetic coil (MC) and to determine the optimal reliable MC position for eliciting motor evoked potentials. The authors have also determined the site of excitation to analyze the validity and potential advantages of this technique as a means of neurophysiologically studying the oculomotor and abducens nerves. The potentials of both of these muscles are evoked by MC placed to be symmetrical to the line connecting the vertex and the center of the eyeball on the side being examined, as the coil center corresponds to the midpoint of this line. The latencies of the motor responses of the superior rectus and lateral rectus were 1.08 +/- 0.22 and 1.02 +/- 0.21 msec, respectively, suggesting that magnetic stimulation excites both the oculomotor and the abducens nerve at the superior orbital fissure.