VOR baseline and adaptation.
(A) Compensatory eye movements, aimed at minimizing retinal slip caused by visual and/or vestibular input, were used to test motor performance in L7-SK2 mice. L7-SK2 mice (n = 10) and controls (n = 26) were head-fixed on a table, and sinusoidal rotation (0.1–1.0 Hz) of the surrounding screen or the table evoked reflexive eye movements that were recorded by a table-mounted camera with IR lights. (B) Gain (measure of eye movement amplitude) and phase (measure of timing of the OKR evoked by rotation of the screen) did not differ between L7-SK2 and control mice. (C) The VOR, evoked by table rotation in the dark, was affected in L7-SK2 mice; both gain and phase were significantly impaired. (D) The combination of vestibular and visual input by rotation of the mouse in the light evoked the VVOR. With visual input, the VOR deficits in L7-SK2 were no longer present. (E) Next, mismatched visual and vestibular input was used to trigger adaptation of the eye movements in order to test motor-learning abilities in L7-SK2 mice. Training sessions (see cartoons) consisted of in-phase rotation of the vestibular and visual input with the same amplitude (5°, 0.6 Hz) on the first training day (day 1, also referred to as VOR gain decrease) and increasing amplitude of the visual input on days 2, 3, and 4. This training induced a reversal of VOR phase (from head to left = eyes to right to head to left = eyes to left), probed by VOR recordings in the dark (plotted data). L7-SK2 mice reversed their VOR phase faster than controls, with significantly higher phase values on all days. (F) Directly following the phase-reversal training, the OKR was probed again to determine OKR gain increase. Both L7-SK2 and control mice were able to increase their OKR gain compared to pretraining values in B. (G) Finally, the ability to perform VOR gain increase was also tested by subjecting mice to out-of-phase visual and vestibular input (5°, 0.6 Hz). Here, no effect of the mutation was observed in the ability to adapt the VOR gain. All data are mean ± SEM (note: for some data points, the error bars are obscured by the marker). *p < 0.05; **p < 0.01; ***p < 0.001. See also S4 Table. IR, infrared; OKR, optokinetic reflex; SEM, standard error of the mean; VOR, vestibulo-ocular reflex; VVOR, visually enhanced VOR.