Electrophysiological evidence for crossed oligosynaptic trigemino-facial connections in normal man.

A crossed short latency component (R1) of the human blink reflex could be elicited in orbicularis oculi muscles to stimulation of the contralateral supraorbital nerve, when infraliminal conditioning stimuli were applied to various cutaneous afferents of the body (facial, upper and lower limbs). The crossed R1 responses appeared when the time interval between the conditioning and the test stimuli was of 30 to 40 ms, 50 to 65 ms and 95 to 110 ms for facial, upper and lower limbs afferents respectively. For the same time intervals, these conditioning volleys also exerted a facilitatory effect on the ipsilateral R1 responses. Furthermore, crossed R1 responses were also obtained during supraspinal facilitation induced by a voluntary contraction of the eyelids. These data show that crossed oligosynaptic trigemino-facial reflex connections exist in normal subjects, which become functional when adequate conditioning stimuli are available.