Maintained ocular torsion produced by bilateral and unilateral galvanic (DC) vestibular stimulation in humans

• Published in: Experimental brain research Vol. 122; no. 4; pp. 453 - 458
• Main Authors: WATSON, S. R. D, BRIZUELA, A. E, CURTHOYS, I. S, COLEBATCH, J. G, MACDOUGALL, H. G, HALMAGYI, G. M
• Format: Journal Article
• Language: English
• Published: Berlin Springer 01.10.1998
• Subjects: Adult; Biological and medical sciences; Electric Stimulation; Eye Movements - physiology; Functional Laterality - physiology; Fundamental and applied biological sciences. Psychology; Humans; Middle Aged; Motor control and motor pathways. Reflexes. Control centers of vegetative functions. Vestibular system and equilibration; Reference Values; Space life sciences; Torsion Abnormality; Vertebrates: nervous system and sense organs; Vestibule, Labyrinth - physiology; Videotape Recording; Human; Galvanic vestibular test; Otolith; Vestibular system; Galvanic current; Eye movement; Torsion; Inner ear
• ISSN: 0014-4819; 1432-1106
• DOI: 10.1007/s002210050533

This study was designed to measure ocular movements evoked by galvanic (DC) stimulation using computerised video-oculography. Long duration (>30 s) galvanic vestibular stimulation at currents of up to 5 mA through large-area surface electrodes over the mastoid processes causes maintained changes in the ocular torsional position of both eyes in healthy human subjects. With the subject seated and the head held firmly, torsion was measured by a computer-based image-processing system (VTM). Torsion was recorded in darkness, with or without a single fixation point. With bilateral stimulation, the upper poles of both eyes always torted away from the side of cathode placement and toward the anode. For unilateral stimulation, torsion was directed away from the cathode or toward the anode. The magnitude of ocular torsion was dependent on current strength: with bilateral stimulation the peak torsion was on average 2.88 degrees for 5-mA current intensity compared with 1.58 degrees for 3 mA. A smaller amplitude of torsion was obtained for unilateral stimulation. The average peak torsion was the same for both eyes for all forms of stimulation. Our findings indicate that low-intensity galvanic stimulation evokes ocular torsion in normal subjects, an effect which is consistent with an action on otolith afferents.