Human 3-D aVOR with and without otolith stimulation

Abstract

We describe in detail the frequency response of the human three-dimensional angular vestibulo-ocular response (3-D aVOR) over a frequency range of 0.05-1 Hz. Gain and phase of the human aVOR were determined for passive head rotations in the dark, with the rotation axis either aligned with or perpendicular to the direction of gravity (earth-vertical or earth-horizontal). In the latter case, the oscillations dynamically stimulated both the otolith organs and the semi-circular canals. We conducted experiments in pitch and yaw, and compared the results with previously-published roll data. Regardless of the axis of rotation and the orientation of the subject, the gain in aVOR increased with frequency to about 0.3 Hz, and was approximately constant from 0.3 to 1 Hz. The aVOR gain during pitch and yaw rotations was larger than during roll rotations. Otolith and canal cues combined differently depending upon the axis of rotation: for torsional and pitch rotations, aVOR gain was higher with otolith input; for yaw rotations the aVOR was not affected by otolith stimulation. There was a phase lead in all three dimensions for frequencies below 0.3 Hz when only the canals were stimulated. For roll and pitch rotations this phase lead vanished with dynamic otolith stimulation. In contrast, the horizontal phase showed no improvement with additional otolith input during yaw rotations. The lack of a significant otolith contribution to the yaw aVOR was observed when subjects were supine, prone or lying on their sides. Our results confirm studies with less-natural stimuli (off-vertical axis rotation) that the otoliths contribute a head-rotation signal to the aVOR. However, the magnitude of the contribution depends on the axis of rotation, with the gain in otolith-canal crosscoupling being smallest for yaw axis rotations. This could be because, in humans, typical yaw head movements will stimulate the otoliths to a much lesser extent then typical pitch and roll head movements.

Reducing pain by moving? A commentary on Ferrè et al. 2013

“…The peak velocity (the relevant stimulus for the vestibular system) was 30 deg/s at all frequencies. Testing of sinusoidal stimuli at different frequencies was necessary to obtain a sustained cover of the spectrum of natural angular stimulation of the vestibular response (Fernandez & Goldberg, 1971;Leigh & Zee, 2006) and, concurrently, provided a frequency response characterization in line with previous vestibular studies (Bockisch, Straumann, & Haslwanter, 2005). …”

Cox’s Chair Revisited: Can Spinning Alter Mood States?

“…As described previously (30) the three-axis rotational stimulator is driven by three servo-controlled motorized axes (Acutronic, Switzerland), controlled with Acutrol software and hardware, and interfaced with Lab VIEW software. Subjects are comfortably seated in a chair and secured with safety belts.…”

“…Individually adjusted masks (Simmed BV, Reeuwijk, The Netherlands), made of a thermoplastic material (Posicast), were molded to the contour of the head after warming with an opening in the mask made for the mouth. The mask is attached to the back of the chair, and restricts head movements very effectively without causing discomfort (30). …”

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“…A second possibility is that otolith signals are part of the response (Angelaki and Dickman 2003; Bockisch et al 2005). The contribution of tilt VOR to the 3D eye velocity response depends on the orientation of the stimulus axis (Merfeld 1995; Merfeld et al 2005).…”

“…Most head movements are not restricted to a single rotation about one particular axis such as yaw, pitch, or roll but are composed of 3D translations and rotations about an axis with different orientation and amplitudes in 3D space (Grossman et al 1989; Crane and Demer 1997). The contribution and interaction of the different parts of the vestibular system (canals and otoliths) on ocular stabilization has been investigated in many studies (Groen et al 1999; Schmid-Priscoveanu et al 2000; Bockisch et al 2005; for a review, see also Angelaki and Cullen 2008). Although the quality of the VOR response is usually quantified by the gain (ratio between eye and head velocity), alignment of the eye rotation axis with respect to the head rotation axis is also an important determinant.…”