Trigeminal-hypoglossal silent period: a pontomedullary brainstem reflex.

INTRODUCTION

Animal studies have shown inhibitory connections between the sensory trigeminal nucleus and hypoglossal nucleus. I investigated whether these inhibitory projections are present in humans.

METHODS

I examined 18 healthy subjects, 2 patients with brainstem stroke, and 5 patients with multiple sclerosis using a specially designed oral stimulation and recording device.

RESULTS

In 16 of 18 subjects, a bilateral suppression period of tongue muscle activity after unilateral electrical stimulation of the mucosal V2 afferents was observed. The silent period started at 31.1 (SD 4.7) ms (ipsilateral) and 32.0 (SD 4.9) ms (contralateral). The mean duration of the silent period was 31.4 (SD 10.2) ms (ispilateral) and 32.5 (SD 9.8) ms (contralateral). Patients with dorsolateral pontomedullary lesions had ipsilateral absence of the silent period.

CONCLUSIONS

This study confirms the existence of a bilateral trigeminal-hypoglossal silent period in humans.