To assess the contributions of the vestibular system to whole-body motion discrimination in the dark, we measured direction-recognition thresholds as a function of frequency for yaw rotation, superior-inferior translation (“z-translation”), inter-aural translation (“y-translation”), and roll-tilt for 14 normal subjects and for three patients following total bilateral vestibular ablation. The patients had significantly higher average threshold measurements than normal (p<0.01) for yaw-rotation (depending upon frequency, 5.4× to 15.7× greater), z-translation (8.3× to 56.8× greater), y-translation (1.7× to 4.5× greater), and roll tilt (1.3× to 3.0× greater) – establishing the predominant contributions of the vestibular system for these motions in the dark.

Vestibular symptoms caused by migraine, referred to as vestibular migraine, are a frequently diagnosed but poorly understood entity. Based on recent evidence that normal subjects generate vestibular-mediated percepts of head motion and reflexive eye movements using different mechanisms, we hypothesized that percepts of head motion may be abnormal in vestibular migraine. We therefore measured motion detection thresholds in patients with vestibular migraine, migraine patients with no history of vestibular symptoms, and normal subjects using the following paradigms: roll rotation while supine (dynamically activating the semicircular canals); quasi-static roll tilt (statically activating the otolith organs); and dynamic roll tilt (dynamically activating the canals and otoliths). Thresholds were determined while patients were asymptomatic using a staircase paradigm, whereby the peak acceleration of the motion was decreased or increased based on correct or incorrect reports of movement direction. We found a dramatic reduction in motion thresholds in vestibular migraine compared to normal and migraine subjects in the dynamic roll tilt paradigm, but normal thresholds in the roll rotation and quasi-static roll tilt paradigms. These results suggest that patients with vestibular migraine may have enhanced perceptual sensitivity (e.g. increased signal-to-noise ratio) for head motions that dynamically modulate canal and otolith inputs together.

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