Motor-evoked potentials of tongue musculature in dogs

Transcranial brain stimulation by either electrical or noninvasive magnetic stimulation has produced motor responses of limb musculature. However, recordings from muscles innervated by cranial nerves have not previously been reported. A right-sided craniotomy was performed in 18 dogs. An electric stimulus was delivered to the motor cortex via surface electrodes and evoked EMG responses were recorded from the tongue musculature to determine conduction time. Magnetic stimulation of the motor cortex yielded EMG latencies similar to those obtained by electrical direct cortical stimulation, thus demonstrating the potential of magnetic stimulation in intraoperative and outpatient clinical evaluation of hypoglossal nerve disorders. For the first time, it appears possible to noninvasively stimulate the cranial nerves proximal to the point of injury and to evaluate more central conduction pathways.