Displacement of listing's plane by galvanic vestibular stimulation measured by 3-dimensional video-oculography

Saccadic eye movements are located in Listings plane (LP). Activation of the semicircular canals moves the eye positions out of LP, whereas activation of the otolith organs shifts LP. Bipolar galvanic vestibular stimulation (GVS) with DC current stimulates the vestibular periphery, and it is thought to resemble virtual rotations mainly in roll. Eye positions were measured with 3-dimensional (3-D) video-oculography, using sclera markers to determine the ocular torsion. The subjects were seated in darkness, with the head fixed in the upright position, and instructed to perform a saccade when the visual target appeared. GVS was applied in blocks of 10 s. During GVS, subjects showed nystagmus. Eye positions moved out of LP and returned with a torsional offset. Only positions after saccadic eye movements were selected to evaluate that offset. In a group of four healthy subjects, the mean offset to LP was 0.4 degrees (mean current 2.5 mA), with a SD that was greater for GVS (1.0 degrees) than for the control condition (0.4 degrees).