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We showed previously that smooth pursuit training combined with whole-body rotation in the orthogonal plane induces adaptive cross-axis vestibulo-ocular reflex (VOR). To gain an insight into the possible pathways and the nature of error signals for cross-axis VOR adaptation, we examined further properties of adaptive responses. In the first series, we trained monkeys for vertical pursuit during sinusoidal yaw rotation at 0.5 Hz (± 10°) by presenting a target spot either in phase with, or with phase shifts (lead or lag) of 90° to, the chair for 1 h. After training, sinusoidal or trapezoidal yaw rotation was tested in complete darkness without a target. Different training conditions resulted in different amounts of phase shift in cross-axis VOR. Trapezoidal yaw rotation (peak acceleration ≈ 780°/s[sup 2]) revealed further differences in the direction, latency and time course of the adaptive responses depending on the conditions of the pursuit task. At least two (fast and slow) components with different latencies were induced in the cross-axis VOR by trapezoidal rotation after in-phase and phase-shift training. Adaptive responses were accurately simulated by the weighted sum of these two components. In the second series, we examined the effects of sequentially flashed (10 μs) targets in the horizontal plane during pitch rotation. The monkeys learned to track such targets by smooth pursuit, and cross-axis VOR was also induced after such apparent motion stimuli without retinal slip of the target image. These results indicate the importance of eye velocity for cross-axis VOR and suggest that this adaptation occurs most probably in the smooth pursuit pathways. [ABSTRACT FROM AUTHOR]

The present research analysed on chronic animals the functional recovery of eye motility after impairment of the proprioceptive input at the level of the semilunar ganglion. The horizontal vestibulo-ocular reflex (HVOR) was recorded in normal pigmented rabbits before and after a partial electrolytic lesion of the semilunar ganglion. The recordings were repeated daily for 8-10 days to evaluate the recovery. Immediately after the lesion, as previously observed, HVOR slow phases were unaffected, while quick phases (QPs) showed a reduction in peak velocity and a deviation of trajectories from the horizontal plane. QP peak velocity was almost completely restored within 3-5 days, while trajectory deviation was not corrected during the observation period. Furthermore, in some animals, the variability of trajectories showed, starting from days 3-5, a progressive increase that led to a greater spatial disorganization. A process of lesion-induced plasticity takes place, but only the velocity of QPs can be recovered rapidly, while the QP trajectory impairment does not appear to be compensated substantially, which underlines a determinant role in the control of QP spatial orientation exerted by EOM proprioceptive signals. [ABSTRACT FROM AUTHOR]

We showed previously that smooth pursuit training combined with whole-body rotation in the orthogonal plane induces adaptive cross-axis vestibulo-ocular reflex (VOR). To gain an insight into the possible pathways and the nature of error signals for cross-axis VOR adaptation, we examined further properties of adaptive responses. In the first series, we trained monkeys for vertical pursuit during sinusoidal yaw rotation at 0.5 Hz ( ±10°) by presenting a target spot either in phase with, or with phase shifts (lead or lag) of 90° to, the chair for 1 h. After training, sinusoidal or trapezoidal yaw rotation was tested in complete darkness without a target. Different training conditions resulted in different amounts of phase shift in cross-axis VOR. Trapezoidal yaw rotation (peak acceleration ≈780°/s 2 ) revealed further differences in the direction, latency and time course of the adaptive responses depending on the conditions of the pursuit task. At least two (fast and slow) components with different latencies were induced in the cross-axis VOR by trapezoidal rotation after in-phase and phase-shift training. Adaptive responses were accurately simulated by the weighted sum of these two components. In the second series, we examined the effects of sequentially flashed (10 μs) targets in the horizontal plane during pitch rotation. The monkeys learned to track such targets by smooth pursuit, and cross-axis VOR was also induced after such apparent motion stimuli without retinal slip of the target image. These results indicate the importance of eye velocity for cross-axis VOR and suggest that this adaptation occurs most probably in the smooth pursuit pathways. [ABSTRACT FROM AUTHOR]

We investigated the orientation of quick phases (QPs) of vestibularly-induced eye movements in rabbits in response to ''off-vertical'' sinusoidal vestibular stimulation. We also examined the possible role of the cerebellar nodulus and ventral uvula in controlling QP spatial orientation and modification. 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 gravito-inertial coordinates and SPs in head coordinates. When rabbits were oscillated in the light (20° peak-to-peak; 0.2 Hz) about an ''off-vertical'' 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 the earth's horizontal plane even after 2 h of ''off-vertical'' stimulation. The conjunctive combination of optokinetic and vestibular stimulation caused QPs to change their plane of rotation. After lesion of the nodulus-uvula the ability of rabbits to reorient QPs during conjoint vestibular-optokinetic stimulation was maintained. We conclude that the space orientation and adaptation of QPs do not require cerebellar control. [ABSTRACT FROM AUTHOR]