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. 2017 Feb 8:7:42071.
doi: 10.1038/srep42071.

Ocular Reflex Phase during Off-Vertical Axis Rotation in Humans is Modified by Head-Turn-On-Trunk Position

Samantha B Douglas  1 , Gilles Clément  2 , Pierre Denise  3 , Scott J Wood  1
Affiliations

Ocular Reflex Phase during Off-Vertical Axis Rotation in Humans is Modified by Head-Turn-On-Trunk Position

Samantha B Douglas et al. Sci Rep. .

Abstract

Constant velocity Off-Vertical Axis Rotation (OVAR) imposes a continuously varying orientation of the head and body relative to gravity, which generates a modulation of horizontal (conjugate and vergence), vertical, and torsional eye movements. We introduced the head-turn-on-trunk paradigm during OVAR to examine the extent to whether the modulation of these ocular reflexes is mediated by graviceptors in the head, i.e., otoliths, versus other body graviceptors. Ten human subjects were rotated in darkness about their longitudinal axis 20° off-vertical at a constant velocity of 45 and 180°/s, corresponding to 0.125 and 0.5 Hz. Binocular responses were obtained with the head and trunk aligned, and then with the head turned relative to the trunk 40° to the right or left of center. The modulation of vertical and torsional eye position was greater at 0.125 Hz while the modulation of horizontal and vergence slow phase velocity was greater at 0.5 Hz. The amplitude modulation was not significantly altered by head-on-trunk position, but the phases shifted towards alignment with the head. These results are consistent with the modulation of ocular reflexes during OVAR being primarily mediated by the otoliths in response to the sinusoidally varying linear acceleration along the interaural and naso-occipital head axis.

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Conflict of interest statement

The authors declare no competing financial interests.

Figures

Figure 1
Figure 1. Recordings of torsional (blue) and vertical (red) eye movements in one typical subject with the head aligned with the trunk during several cycles of OVAR in darkness at both 0.125 Hz and 0.5 Hz.
The torsional eye position was modulated by the continuously varying roll tilt (blue) and vertical eye position was modulated by the continuously varying pitch tilt (red).
Figure 2
Figure 2. Recordings of horizontal (blue) and vergence (red) slow phase eye velocity (SPV) in one typical subject with the head aligned with the trunk during several cycles of OVAR in darkness at both 0.125 Hz and 0.5 Hz.
The horizontal SPV was modulated by the sinusoidally varying linear velocity about the head inter-aural axis (blue). The vergence SPV was modulated by the sinusoidally varying linear velocity about the head naso-occipital axis (red).
Figure 3
Figure 3. Amplitude and phase of torsional (Tor) and vertical (Ver) eye position during OVAR at 0.125 Hz and 0.5 Hz for various head-turn-on-trunk (HTOT) positions.
Mean ± Standard deviation of all 10 subjects.
Figure 4
Figure 4. Amplitude and phase of horizontal (Hor) and vergence (Ver) slow phase eye velocity (SPV) during OVAR at 0.125 Hz and 0.5 Hz for various head-turn-on-trunk (HTOT) positions.
Mean ± Standard deviation of all 10 subjects.
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