Somatosensory evoked potentials following tongue stimulation in normal subjects and patients with lesions of the afferent trigeminal system.

Somatosensory evoked potentials (SEPs) after unilateral stimulation of the tongue were recorded in 20 normal subjects and in 20 patients with peripheral and central lesions of the afferent trigeminal pathway. Potentials were recorded up to 50 msec latency via electrodes placed on the scalp (between C3/4 and T3/4), the tragus and intra-orally with a fronto-central reference. In several instances simultaneous records from facial and masticatory muscles were obtained in order to detect muscle artifacts. (1) Very early components up to 5 msec were contaminated by muscular artifacts arising from muscle twitch of the tip of the tongue. (2) Reflex potentials could be recorded over the tragus at latencies between 15 and 25 msec when the jaw-opening muscles were preactivated but not during relaxation. (3) A positive potential with a latency of 21 msec and maximum amplitude over the contralateral scalp was present in all normal subjects and on the non-affected sides of all patients. (4) Cortical SEPs were absent in 19 of the 20 patients with central or peripheral lesions of the lingual nerve pathway (presenting clinically with neuralgia, hypoaesthesia or anaesthesia). In one patient a delayed potential was recorded. Lingual nerve SEPs provide a useful tool for monitoring lingual nerve function. As with other SEP techniques, no conclusions concerning the type and extent of the underlying pathology can be drawn.