Role of cerebellar nodulus and uvula on the vestibular quick phase spatialconstancy

We investigated the orientation of quick phases (QPs) of vestibularly-induc ed eye movements in rabbits in response to "off-vertical" sinusoidal vestib ular stimulation. We also examined the possible role of the cerebellar nodu lus arid ventral uvula in controlling QP spatial orientation and modificati on. During "off-vertical" vestibular stimulation QPS remained aligned with the earth's horizontal plane, while the slow phases (SPs) were aligned with the plane of vestibular stimulation. This suggests that QPs are coded in g ravito-inertial coordinates and SPs in head coordinates. When rabbits were oscillated in the light (20 degrees peak-to-peak; 0.2 Hz) about an "off-ver tical" axis for 2 h, the QPs changed their trajectory, abandoning the earth 's horizontal plane to approach the plane of the stimulus. By contrast, in the absence of conjunctive optokinetic stimulation, QPs remained fixed in t he earth's horizontal plane even after 2 h of "off-vertical" stimulation. T he conjunctive combination of optokinetic and vestibular stimulation caused QPs to change their plane of rotation. After lesion of the nodulus-uvula t he ability of rabbits to reorient QPs during conjoint vestibular-optokineti c stimulation was maintained. We conclude that the space orientation and ad aptation of QPs do not require cerebellar control.