Study of pursuit and vestibulo-ocular cancellation.

This present study, a follow-up of our earlier investigation, further examines the time courses of recovery of oculomotor and vestibular function while patients are under the sedative effect of a single dose of secobarbital (Seconal). The assessment included tests for saccade and smooth pursuit, and the vestibulo-ocular reflex and its cancellation, as evaluated by sinusoidal and pseudorandom rotation in a high-frequency hydraulic chair (up to 5 Hz). Analysis of results showed that the vestibulo-ocular reflex (VOR) gain, depressed soon after drug intake, recovered substantially after a few hours. Changes in VOR gain were more pronounced with higher frequencies of rotation at 2 and 3 Hz, and greater with pseudorandom than sinusoidal stimulation. Under barbiturate influence, pursuit and VOR cancellation followed distinctly different time courses of recovery. This dissociation between VOR cancellation and pursuit supports the theory that these two systems are subserved by different mechanisms. Saccadic hypermetria was also observed after drug intake.