Changes in the blink responses to combined trigeminal, acoustic and visual repetitive stimulation, studied in the human subject.

Habituation of blink reflexes as measured by amplitude decrement in the orbicularis oculi EMG was examined in 9 human subjects using combinations of repetitive electric stimuli to the bridge of the nose (trigeminal stim.), short clicks (acoustic stim.), and flashes (visual stim.). With trains of paired stimuli, both homogeneous and mixed, habituation was increased when the two stimuli were separated by 250 msec but was decreased when the interval was 30 (50) msec, as compared to single stimulus trains of identical repetition rate. Following acoustic or visual prehabituation the habituation to trigeminal stimuli was enhanced. This "transfer of habituation' was also obtained with acoustic before visual stimuli and vice versa. Regarding dishabituation, interposition of single extrastimuli, for example visual or acoustic within repeated trigeminal stimulation, was more effective than a simple pause by omitting one electric pulse. The results suggest the existence of a pool of interneurones that is that the common final relay for the blink relfex afferents from the trigeminal, acoustic and visual input.