Large and small coils in magnetic stimulation of the proximal portion of the facial nerve.

Abstract

Magnetic stimulation (Magstim model 200) was performed with a large coil (14 cm in diameter) and a small coil (7 cm in diameter) in 12 healthy persons. Muscle potentials were obtained from ipsilateral orbicularis oris and nasalis muscles when magnetic stimulation was performed by placing a large or small magnetic coil at T6 or by placing a large magnetic coil at C4. The latency obtained by placing a magnetic coil at T6 was 1.2-1.3 ms (with a large coil) and 1.3-1.4 ms (with a small coil) longer, and the latency obtained by placing a large magnetic coil at C4 was 1.3-1.4 ms longer than the latencies obtained by stimulating at the stylomastoid foramen. The proximal portion of the facial nerve is considered to be stimulated transcranially when magnetic stimulation is performed by placing either a large or small coil at T6 or by placing a large coil at C4.