Plasticity in the vestibule-ocular reflex and its application for rehabilitation for the patients with peripheral vestibular disorders

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To elucidate the optical parameters in the training procedure for the patients with peripheral vestibular disorders, we investigated the usefulness of the sinusoidal off-vertical axis rotation (OVAR) to evaluate the otolith function in the healthy subjects (n=8), plasticity in the vestibule-ocular reflex (VOK) (n=9).In the sinusoidal nose-down OVAR, all subjects showed significant VOR gain reduction (p<0.05) in the OVAR at 0.8Hz compared with earth vertical axis relation (EVAR) at 0.8Hz. We concluded that the sinusoidal nose-down OVAR at 0.8Hz may evaluate the otolith function without discomfort for the patients with otolith disorders.In the plasticity experiments, 7 of the subjects who participated in the x2 adaptation experiment at 0.3 Hz and 30° amplitude showed a steady increase of VOR gain within a couple of trials. One of the remaining 2 subjects showed a decrease in VOR gain in all the three trials, and *ther subject showed a VOR gain increase in three trials and decrease in 2 trials. In the x2 adaptation experiment at 0.3 Hz and 80° amplitude (peak velocity : 28°/s), the percentage gain change ((post-pre)/pre) was 133% at the same stimulation and 100% at 0.4 Hz (peak velocity : 37°/s). The gain change was 65% at 0.1 Hz and 60° amplitude (peak velocity : 18%/s), and 64% at 0.2 Hz and 60° amplitude (peak velocity : 37° /s). In the xl adaptation experiment (30° at 0.3 Hz), the percentage gain change was -62% under the same conditions, 50% at 0.1 Hz and 60° amplitude, and -30% at 0.2 Hz and 60° amplitude. No change of VOR gain was observed at other frequencies, and the subject was not adapted at 0.1 Hz and 30° amplitude. The larger VOR gain increase in the x2 adaptation experiment for the faster head angular acceleration leads to the conclusion that the VOR gain mechanism can set very different gain states for the VOR that are quite similar in terms of the head acceleration.