Vincent Lagadec

Background: Impaired vestibulo-ocular reflex (VOR) can be compensated by catch-up saccades and/or increased residual VOR. Prediction and intention seem able to potentiate both responses, but how do these effects combine, particularly in individuals with bilateral vestibulopathy (BVP), remains largely unknown. Objective: To compare the impact of passive, predictive and voluntary conditions of head impulse tests (HIT) on global oculomotor compensatory responses in individual with BVP. Methods: HIT were performed in Passive(P)-Random, Passive(P)-Cued and Active head movement conditions. VOR gain and latency and gain of the 1 ^st catch up saccades were calculated for the 32 tested ears. Among the 1 ^st catch up saccade, a separate analysis of covert saccades was performed. Results: Latency of covert saccades was shorter in the Active compared to P-Random and P-Cued. First saccades showed shorter latency and greater gain in the P-Cued condition versus P-Random. VOR gain was significantly higher in the Active condition compared to P-Random and P-Cued. Most individuals enhanced catch-up saccades and VOR gain simultaneously while others either boosted VOR gain while reducing saccade efficiency, or enhanced saccade efficiency while decreasing VOR gain. Conclusions: Prediction and intention improve gaze during HIT in individuals with BVP by optimising existent oculomotor responses. During active movements, these effects combined according to subjects’ individual strategies.