Eye instability induced by vestibular stimulation in rabbits

The slow compensatory phases of the vestibule-ocular reflex (VOR) in the ra bbit tend to drift and the drift reverses the direction. This periodic alte rnating drift (PAD) has two peculiar characteristics: (I) it is induced by sinusoidal vestibular stimulation in naive animals, being evoked immediatel y after stimulus onset and persisting after the end of stimulation; (2) the peak velocity and period of the drift are dependent on stimulus amplitude. PAD of the rabbit has strong similarities with PAN, a periodic alternating nystagmus observed in humans with cerbellar disorders and in monkeys after nodulo-uvulectomy, although its peak velocity is smaller. It is hypothesiz ed that PAD is due to a slight instability, caused by vestibular stimulatio n in darkness, of the cerebellar adaptive loop, which exerts a variable gai n control on the time constant of the velocity storage integrator. NeuroRep ort 12:1847-1850 (C) 2001 Lippincott Williams & Wilkins.