Voluntary movement and excitability of cutaneous eyeblink reflexes.

Abstract

ABSTRACTReflex responses from eyelid muscles were evaluated when subjects prepared to or made brief or sustained voluntary contractions of eyelid or forearm muscles in a signaled reaction time task. The eyeblink reflex consists of an early and unilateral response, R1, and a longer latency bilateral response, R2. A similar pattern of reflex excitability was observed for all phasic movements. The R1 was transiently potentiated by the warning stimulus, increased again at the end of the preparatory period, increased more in the reaction interval and immediately after movement onset, and finally declined to control levels by 500 ms after onset of voluntary movement. The R2 responses were typically depressed at the same times that R1 responses were enhanced. When sustained contractions were performed and reflexes were elicited after movement eyelid onset, the patterns of early R1 enhancement and R2 depression occurred, both for about 500 ms, and gave way to continued R1 and also R2 enhancement as long as eyelid movement continued. The different behavioral responses of R1 and R2 reflect differences in the physiological properties of the separable neuroanatomical pathways for the two eyelid reflex responses.