Different forms of blinks and their two-stage control.

The purpose of this paper is to examine blink kinematics and the neural basis of blinks evoked reflexively by different kinds of stimuli. The kinematics of the upper lid movement and the electromyographic response of lid muscles levator palpebrae and orbicularis oculi were recorded in the rabbit during trigeminally and visually-evoked blinks. We find that there is a basic, kinematic difference between blinks. A blink in response to an airpuff is more rapidly accomplished and achieves a higher velocity than does an equal amplitude blink in response to a flash of light. The two forms of the reflex blink result from differences in the nature and timing of activity in antagonistic lid muscle motoneurons. Nevertheless, most characteristics of blink neural control are common to both reflex blinks. Most importantly, it appears that blinks are produced by two-stage neural control, an early component that is preprogrammed and a late component that is under stimulus control.