The excitation site of the accessory nerve to the magnetic stimulation ± the relationship between the orientation of the magnetic ®eld and the excitation site

Objective: The relationship between the accessory nerve excitation site and the magnetic field direction was investigated to prove whether the cranial nerve excitation site to the transcranial magnetic stimulation is constant or not. Methods: Compound muscle action potentials (CMAPs) elicited by the transcranial magnetic stimulation were recorded from the trapezius muscles of 7 adult cats. The waveforms of CMAPs were detected before craniectomy, after craniectomy, and after cutting the accessory nerve at the C1, at the jugular tubercle, and at the jugular foramen. The optimal orientation was determined by rotating the coil clockwise in increments of 22.5° from the rostral direction. Results: The accessory nerve was stimulated by the magnetic stimulation at the C1, at the jugular tubercle or at the jubular foramen, and these excitation sites varied with coil orientation. The average angles of the optimal orientation of the magnetic coil were 77.1° for C1, 122.1–263.6° for the jugular tubercle, and 308.6–32.1° for the jugular foramen. Conclusions: The accessory nerve excitation site varied with the orientation of the magnetic coil. This study suggested the possibility of a variety of the cranial nerve excitation sites to the transcranial magnetic stimulation.