Visual input to the hypoglossal nucleus.

Photic stimulation of the retina elicits in the mediocaudal part of the XIIth nucleus the appearance of pronounced field potentials and responses of single hypoglossal units. The latency of the evoked potentials, characterized by a complex sequence of positive-negative waves, was 32.75 +/- 2.5 ms for the initial component p1, 42.25 +/- 3.30 ms for n1, 49.75 +/- 3.09 ms for p2, and 67 +/- 3.94 ms for n2. The hypoglossal neurons, antidromically identified by electrical stimulation of the XIIth nerve, responded with several combinations of excitation-inhibition at various latencies. Nineteen percent of the units responded to both retinae and 10% only to one retina, mainly to the contralateral one. As the mediocaudal part of the hypoglossal nucleus receives vestibular information, it can be concluded that the hypoglossal units adjust their firing in relation to head position and also by using visual information.