VOLUNTARY EYELID CONTRACTION MODIFIES THE BLINK REFLEX RECOVERY CYCLE

In order to determine the extent to which the recovery cycle of the bl ink reflex is modified by voluntary contraction of the eyelids we inve stigated the electrically elicited blink reflex with paired stimuli of identical intensity in 9 healthy subjects. We pseudorandomly administ ered two interstimulus intervals (150 ms and 250 ms) in three differen t conditions of voluntary contraction of the orbicularis oculi muscle (relaxed, mild lid closure and strong lid closure). Our results show t hat inhibition of the R2 response following the second stimulus is sig nificantly reduced with voluntary contraction. In addition, we found s ignificantly larger amplitudes and shorter latencies of R1 and R2 with voluntary contraction. We conclude that in healthy subjects, voluntar y eyelid contraction causes facilitation or disinhibition not only in the nuclei of the seventh cranial nerve, but also in the polysynaptic pathway of the R2. The possible implications on the interpretation of clinical data are discussed.