Rapid acclimatization to baseline stimulation with a multi-canal vestibulocochlear implant

It is hypothesized that a vestibular implant should re-establish baseline activity of the ampullary nerves. Use of a constant baseline stimulation potentially allows encoding of bi-directional head movements, through the addition of signal modulations. Effective stimulation of the vestibular nerves depends on the ability to acclimate to this baseline signal. This study aims to measure eye movement responses and evaluate patient perception after turning ON and OFF single-canal and multi-canal baseline stimulation with a vestibulocochlear implant.

Nine subjects with a multi-canal vestibulocochlear implant were investigated by turning baseline stimulation ON and OFF. Eye movements were recorded at fixed time points. To quantify acclimatization, both the relative time constant (time until the nystagmus decreases to 37% of its initial maximum value) and the absolute time constant (time until the velocity drops below 5°/s) were calculated. Following each recording, patients' perceptions were collected.

A rapid logarithmic decay in response dynamics was observed in all subjects after turning baseline stimulation ON and OFF. Full acclimatization was typically achieved within one minute. The response dynamics were reproducible when tested twice and were comparable when using a stimulation rate of either 100% or 50%. In general, turning baseline stimulation OFF resulted in lower response dynamics compared to ON.

The ability to quickly acclimate to step changes in stimulation amplitude level is beneficial and suggests the presence of efficient neuronal processes that aid in the process of dual-state adaptation. Rapid acclimatization paves the way for safe and convenient use of the implant.

ClinicalTrials.gov: NCT04918745. Registered 28 April 2021.