Correlation between semicircular ocular reflex and otolith ocular reflex and its application for clinical diagnosis using off-vertical axis rotation(OVAR)

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The vestibulo-ocular reflex(VOR) produces compensatory eye movements during head movements. The VOR consists of the angular VOR and the linear VOR. The VOR is under adaptive control that corrects VOR performance when visual-vestibular mismatch arises during head movements. Most experiments concerning plasticity of the VOR have used the semicircular-ocular reflex(ScOR). So far, there has been no investigation on the effect of adaptive plasticity of the otolith-ocular reflex(OOR) on the ScOR. In this study, using a linear sled, we tested the hypothesis that the ScOR is altered by changes in the OOR. To modify the OOR, we used an adaptation paradigm. Eight subjects were rotated sinusoidally at 0.125 Hz and 60 deg/sec peak angular acceleration for 40 minutes, while viewing earth-fixed vertical stripes on the wall while wearing the binocular magnifying lenses (x 2 paradigm). Four subjects were rotated sinusoidally for 40 minutes, while viewing head-fixed LED (x 0 paradigm). In the x 2 paradigm, 6 of the 8 subjects showed an increase in OOR sensitivity after adaptation. Each of the 6 subjects who showed an increase in OOR sensitivity after adaptation also showed an increased ScOR gain at 0.125Hz. In the x 0 paradigm, 2 of the 4 subjects showed a decrease in OOR sensitivity after adaptation. Each of the 2 subjects who showed an decrease in OOR sensitivity after adaptation also showed an decrease ScOR gain at 0.125Hz. These results suggest that the OOR and the ScOR share common neural pathways in such a way that a change in the synaptic efficacy of one pathway is accompanied by a commensurate change in the other.