TO BLINK OR NOT TO BLINK - INHIBITION AND FACILITATION OF REFLEX BLINKS

A reflex blink typically inhibits subsequent blinks. In this study, we investigated whether the nature and time course of this inhibition va ry when different combinations of blink-evoking stimuli are used. We u sed the paired stimulus paradigm, in which two blink-evoking stimuli - a conditioning stimulus followed by a test stimulus - are presented w ith a variety of interstimulus intervals, to examine the interactions between blinks evoked by trigeminal and acoustic stimuli in rats and h umans. In addition, we studied the effect of a blink-evoking trigemina l stimulus on subsequent gaze-evoked blinks in humans. The results rev ealed that long-lasting inhibition occurred when the conditioning and test stimuli were within the same modality. A shorter period of inhibi tion followed by facilitation occurred when the stimuli were in differ ent modalities. The data demonstrate that a blink-evoking stimulus ini tiates a lengthy period of inhibition in its own sensory pathway and a shorter period of inhibition in the reticular formation and/or in bli nk motoneurons. In addition, the results show that the blink-evoking s timulus also initiates a facilitatory process. Thus, the magnitude of a blink reflects a balance between inhibitory and facilitatory process es.