Trigeminal nerve stimulation: short latency somatosensory evoked potentials.

We have devised a technique to measure trigeminal somatosensory evoked potentials, stimulating the mentalis nerve at the mandibular foramen and recording the evoked early potential on the scalp at 3.2 msec. The early potential was easily recognized in all normal subjects and on the asymptomatic side of patients with facial pain. The latency of the early potential in normals was 1 to 2 msec less than half the latency of the mechanically induced jaw jerk. The early potential appeared simultaneously on both sides after stimulation of either the right or left mentalis nerve and may have its origin in deep brainstem structures, the Gasserian ganglion, or the trigeminal nerve. The technique is useful in documenting the functional integrity of peripheral and central afferent pathways of the trigeminal nerve.