The Effect of Bone-Conducted Stimulation on Rotary Chair Time Constants in Patients With Vestibular Migraines

This study is designed to investigate the effects of The Otolith Labs bone conduction device (BCD) on the vestibular system. In the context of this trial, the BCD was designed and developed to reduce the effects of external stimulation of the vestibular system. The eventual intended use of the device is for people who have vestibular disorders (e.g. Vestibular Migraine, Meniere's Disease) who may benefit from a device that can provide a normalizing response to an abnormal vestibular neural signal.

To better understand the functioning principles of the BCD, the investigators want to conduct standard clinical testing using a rotary chair, specifically

• Step velocity testing (SVT) with the chair rotating and vision denied
• Optokinetic testing (OKT) with the chair stationary and visual field moving

Published studies have demonstrated that a reduction in the vestibulo-ocular reflex (VOR) time constants during optokinetic and velocity step testing is correlated with improved motion sickness symptoms. The investigators aim to determine if the BCD similarly reduces the VOR time constant. A reduction in time constant has been shown to be strongly correlated with a reduced time constant of integration in the central velocity storage (a long time constant very strongly correlates with motion sensitivity and with the severity of vestibular migraine episodes.

In this study, the BCD is set at one of three settings- turned off, low power level, high power level, -while the participant is undergoing testing at 60 °/s (patient's own motion for step velocity testing, or projected image for OKT). The same test methodology and equipment shall be used for all participants. In total, 6 rotational tests - one clockwise rotation and one counterclockwise rotation at each of the three power settings, and 6 static tests - with the visual field moving left then right at each of the three power settings, will be conducted and the order of the high/low power settings will be randomized to the second/third set of SVT and OKT. The device is adjusted to a new power level a few seconds before initiating each SVT and OKT.

Eye movements will be tracked during the SVT and OKT to evaluate decay in amplitudes and frequency of nystagmus over time (typically around 15 seconds). Comparison will be made between the three power conditions to evaluate the effect of bone conduction stimulation on the vestibular sense stimulated by rotation.

The participant will be prompted to report on the Fast Motion Scale (FMS) - a simple, validated 20 point verbally reported numerical rating scale - prior to and following each chair session to gauge the momentary level of motion sickness perception. The FMS will be reported a total of 12 times per participant (pre- & post-rotary tests).

Participants will complete the Motion Sickness Sensitivity Questionnaire Short Form (MSSQ-SF) to determine their history of sensitivity to provocative motion. Participants will also complete the Vestibular Migraine Patient Assessment Tool and Handicap Inventory (VM-PATHI) to assess the correlation of the potential change in time constants and VOR gain to the perceived severity of their vestibular migraine condition.

Inclusion criteria

• Definite or probable vestibular migraine
• Residing in the United States

Exclusion criteria

• Head injury (e.g. skull fracture, concussion) within the last six months
• Neurodegenerative disorder
• Recent use of specified medications
• History of:

• Vestibular neuritis / labyrinthitis
• Vestibular schwannoma or acoustic neuroma
• Radiographically unexplored unilateral or sudden sensorineural hearing loss
• History of surgery to the skull base or head,
• Surgery to the middle ear in the past 6 months,
• Surgery to the inner ear (e.g. labyrinthectomy) at any time.
• Eye surgery within the previous 3 months
• Significant reported history of ear disease, intravenous ototoxic medications