Magnetic Transcranial and Electric Direct Stimulation of the Facial Motor Cortex in Dogs

Magnetic stimulation may allow noninvasive study of the entire course of the facial nerve. Our goal was to determine if evoked muscle action potentials can be obtained in facial musculature using electric direct cortical and noninvasive transcranial magnetic stimulation of the canine motor cortex. Thirty-four dogs were studied with electric direct cortical stimulation through a craniotomy and magnetic transcranial stimulation of the facial motor cortex. Facial nerve stimulation in the cerebellopontine angle allowed comparison to cortical responses. Latencies of 6.08 and 9.52 msec for orbicularis oculi and levator nasolabial, respectively, were determined with magnetic transcranial stimulation, compared with 4.22 and 5.78 msec with electric direct cortical stimulation. In conclusion, magnetic stimulation of the facial motor cortex is possible in dogs, with longer central conduction times than with electric direct stimulation.