THE EFFECT OF MAGNETIC COIL ORIENTATION ON THE EXCITATION OF THE MEDIAN NERVE

Objective - We investigated the effect of magnetic coil orientation on the excitation of the median nerve in healthy subjects. Methods - An 8-shaped coil, 3.2 cm in outer diameter, was used. The median nerve wa s stimulated at the elbow while the compound muscle action potentials (CMAPs) of abductor pollicis brevis muscle were recorded at 4 differen t directions of the induced current: orthodromic, antidromic, medio-la teral and latero-medial. Results - We found that the amplitude of the CMAP was the greatest in a medio-lateral (ML) direction. We also measu red the induced electric field in the saline tank that mimicked the fo rearm. The induced electric field and its spatial gradient were the gr eatest in the ML direction among 4 directions. Conclusion - The fact t hat the forearm is a restrictive volume conductor may result in the di fferent effects of coil orientation on the excitation of the median ne rve at the elbow.