Induction of periodic alternating nystagmus in intact goldfish by sinusoidal rotation.

During movement, the vestibulo-ocular reflex (VOR) normally maintains retinal image stability by making slow-phase eye rotations that counterbalance head rotations. These eye rotations are nystagmic when the on-going slow-phases are interrupted by fast-phase eye rotations that reset eye position. Periodic alternating nystagmus (PAN) is an eye-movement disorder characterized by uncontrollable nystagmus that alternates direction roughly sinusoidally (at about 0.005 Hz). PAN has been observed only in humans with cerebellar disorders and in monkeys with lesions to the cerebellar nodulus and uvula. We show experimentally in intact goldfish that prolonged rotation in darkness for 1 h at specific frequencies (0.05-0.1 Hz) induces PAN, upon which the normal VOR response is superimposed. We show computationally that rotation-induced PAN may result from decreased cerebellar inhibition of VOR brain stem neural pathways.