Incremental Vestibulo-ocular Reflex Adaptation Training Dynamically Tailored for Each Individual.

BACKGROUND AND PURPOSE

Unilateral incremental vestibulo-ocular reflex (VOR) adaptation (IVA) increases the VOR gain (= eye/head velocity) for head rotations to one side by ∼10%. Prior IVA studies involved setting the initial VOR training gain demand at the subject's starting value (= 1 in a healthy subject), with the gain preset to increment by 0.1 every 90 seconds over 15 minutes, defined as Static IVA. We determined whether a dynamically calculated gain demand (= "actual gain" + 0.1) would result in greater adaptation, defined as Dynamic IVA.

METHODS

Using a hybrid video-oculography and StableEyes training system, we measured the active (self-generated head impulse) and passive (imposed, unpredictable head impulse) VOR gain in 8 healthy subjects before and after 15 minutes of Static (ie, preset) and Dynamic IVA training consisting of active, leftward and rightward, horizontal head impulses (peak amplitude 15°, peak velocity 150°/s, and peak acceleration 3000°/s). We also measured the active VOR gain during training.

RESULTS

The VOR gain increase toward the adapting side was ∼5% larger after Dynamic compared with Static IVA training (Dynamic: 13.9% ± 5.2%, Static: 9.4% ± 7.3%; P < 0.05).

DISCUSSION AND CONCLUSIONS

Our data suggest that 17°/s retinal image slip (due to the 0.1 gain difference between demand and actual gain) is sufficient to drive robust VOR adaptation. The implications for vestibular rehabilitation are that Dynamic IVA training not only produces better VOR adaptation but also allows more flexible training, for example, training can be spread over several smaller time blocks, without undoing prior adaptation.