Abstract
Internal representation of gravity can be quantified by measuring the subjective visual vertical (SVV). Modulation of verticality perception during head tilts may be perturbed in vestibular disorders causing SVV tilts in the upright head position. This study aimed to determine the influence of head tilts on the estimation of SVV in acute vestibular disorders. We measured the SVV in 37 patients with acute vestibular symptoms due to unilateral vestibular neuritis (VN) (n = 28) and lateral medullary infarction (LMI) (n = 9). Measurements of the SVV were performed under head upright, head tilt 30° and 60° in each direction. Seventeen normal subjects served as the control. In controls, head tilt of 30° produced a contraversive shift of the SVV (the E-effect), and head tilt of 60° generated an ipsiversive shift (the A-effect). Patients with VN showed only the A-effect irrespective of the direction and amplitude of head tilt. Patients with LMI could estimate earth verticality accurately during head tilts. Patients with VN during the recovery phase showed the patterns of SVV modulation similar to those observed in the controls either with head upright or tilted. Given the absence of the E-effect in acute VN, the peripheral otolithic inputs appear to be essential in the perception of earth vertical during small static head tilts.
Highlights
Internal representation of gravity can be quantified in a standard way by setting a luminous rod along the perceived vertical in darkness, the subjective visual vertical (SVV)
With the head tilted 30° in each direction, the SVV tended to be tilted in the opposite direction of the head tilts, but remained within the normal range and did not show a statistical difference from the VPRIMARY (VRED30 = −0.05 ± 2.56°, VLED30 = +0.21 ± 2.84°)
Head tilts 30° caused the shift of SVV in the opposite direction of head tilt, and head tilts 60° caused the shift of SVV in the same direction of head tilt
Summary
Internal representation of gravity can be quantified in a standard way by setting a luminous rod along the perceived vertical in darkness, the subjective visual vertical (SVV). Vestibular, and somatosensory information all contributes to internal estimation of the verticality [1], the otolithic input is most important. The SVV in the head upright position is aligned with the gravitational vertical and the yaw axes of the eyes and head [2]. SVV adjustments are subjected to a systematic bias even in normal subjects, which depends upon the tilt angles. When the head tilt angle is less than 30°, the SVV slightly rotates in the opposite direction of the head tilt, the Müller or E-effect [3]. The tilt angles of about 30°–60° produce rotation
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