Velocity-selective adaptation of the horizontal and cross-axis vestibulo-ocular reflex in the mouse

Abstract

One commonly observed phenomenon of vestibulo-ocular reflex (VOR) adaptation is a frequency-selective change in gain (eye velocity / head velocity) and phase (relative timing between the vestibular stimulus and response) based on the frequency content of the adaptation training stimulus. The neural mechanism behind this type of adaptation is not clear. Our aim was to determine whether there were other parameter-selective effects on VOR adaptation; specifically velocity-selective and acceleration-selective changes in the horizontal VOR gain and phase. We also wanted to determine whether parameter-selectivity was also in place for cross-axis adaptation training (a visual-vestibular training stimulus that elicits a vestibular-evoked torsional eye movement during horizontal head rotations). We measured VOR gain and phase in 17 C57BL/6 mice during baseline (no adaptation training) and after gain-increase, gain-decrease and cross-axis adaptation training using a sinusoidal visual-vestibular (mismatch) stimulus with whole-body rotations (vestibular stimulus) with peak-velocity 20º/s and 50º/s both with a fixed frequency of 0.5 Hz. Our results show pronounced velocity-selectivity of VOR adaptation. The difference in horizontal VOR gain after gain-increase versus gain-decrease adaptation was maximal when the sinusoidal testing stimulus matched the adaptation training stimulus peak-velocity. We also observed similar velocity-selectivity after cross-axis adaptation training. Our data suggest that frequency-selectivity could be a manifestation of both velocity- and acceleration-selectivity because when one of these is absent, e.g., acceleration-selectivity in the mouse, then frequency-selectivity is also reduced.