Blink-perturbed saccades in monkey. I. Behavioral analysis

Saccadic eye movements are thought to be influenced by blinking through pre motor interactions, but it is still unclear how. The present paper describe s the properties of blink-associated eye movements and quantifies the effec t of reflex blinks on the latencies, metrics, and kinematics of saccades in the monkey. In particular, it is examined to what extent the saccadic syst em accounts for blink-related perturbations of the saccade trajectory. Trig eminal reflex blinks were elicited near the onset of visually evoked saccad es by means of air puffs directed on the eye. Reflex blinks were also evoke d during a straight-ahead fixation task. Eye and eyelid movements were meas ured with the magnetic-induction technique. The data show that saccade late ncies were reduced substantially when reflex blinks were evoked prior to th e impending visual saccades as if these saccades were triggered by the blin k. The evoked blinks also caused profound spatial-temporal perturbations of the saccades. Deflections of the saccade trajectory, usually upward, exten ded up to similar to 15 degrees. Saccade peak velocities were reduced, and a two- to threefold increase in saccade duration was typically observed. In general, these perturbations were largely compensated in saccade mid-fligh t, despite the absence of visual feedback, yielding near-normal endpoint ac curacies. Further analysis revealed that blink-perturbed saccades could not be described as a linear superposition of a pure blink-associated eye move ment and an unperturbed saccade. When evoked during straight-ahead fixation , blinks were accompanied by initially upward and slightly abducting eye ro tations of similar to 2-15 degrees. Back and forth wiggles of the eye were frequently seen; but in many cases the return movement was incomplete. Rath er than drifting back to its starting position, the eye then maintained its eccentric orbital position until a downward corrective saccade toward the fixation spot followed. Blink-associated eye movements were quite rapid, al beit slower than saccades, and the velocity-amplitude-duration characterist ics of the initial excursions as well as the return movements were approxim ately linear. These data strongly support the idea that blinks interfere wi th the saccade premotor circuit, presumably upstream from the neural eye-po sition integrator. They also indicated that a neural mechanism, rather than passive elastic restoring forces within the oculomotor plant, underlies th e compensatory behavior. The tight latency coupling between saccades and bl inks is consistent with an inhibition of omnipause neurons by the blink sys tem, suggesting that the observed changes in saccade kinematics arise elsew here in the saccadic premotor system.