We recently discovered that static magnetic fields from high-strength MRI machines induce nystagmus in all normal humans, and that a magneto-hydrodynamic Lorentz force, derived from ionic currents in the endolymph and pushing on the cupula, best explains this effect. Individuals with no labyrinthine function have no nystagmus. The influence of magnetic vestibular stimulation (MVS) in individuals with unilateral deficits in labyrinthine function is unknown and may provide insight into the mechanism of MVS. These individuals should experience MVS, but with a different pattern of nystagmus consistent with their unilateral deficit in labyrinthine function. We recorded eye movements in the static magnetic field of a 7 T MRI machine in nine individuals with unilateral labyrinthine hypofunction, as determined by head impulse testing and vestibular-evoked myogenic potentials (VEMP). Eye movements were recorded using infrared video-oculography. Static head positions were varied in pitch with the body supine, and slow-phase eye velocity (SPV) was assessed. All subjects exhibited predominantly horizontal nystagmus after entering the magnet head-first, lying supine. The SPV direction reversed when entering feet-first. Pitching chin-to-chest caused subjects to reach a null point for horizontal SPV. Right unilateral vestibular hypofunction (UVH) subjects developed slow-phase-up nystagmus and left UVH subjects, slow-phase-down nystagmus. Vertical and torsional components were consistent with superior semicircular canal excitation or inhibition, respectively, of the intact ear. These findings provide compelling support for the hypothesis that MVS is a result of a Lorentz force and suggest that the function of individual structures within the labyrinth can be assessed with MVS. As a novel method of comfortable and sustained labyrinthine stimulation, MVS can provide new insights into vestibular physiology and pathophysiology.
Keywords: vestibular, magnetic, semicircular canals, Lorentz, magneto-hydrodynamics
Citation: Ward BK, Roberts DC, Della Santina CC, Carey JP and Zee DS (2014) Magnetic vestibular stimulation in subjects with unilateral labyrinthine disorders. Front. Neurol. 5:28. doi: 10.3389/fneur.2014.00028
Received: 03 February 2014; Accepted: 27 February 2014;
Published online: 13 March 2014.
Edited by:Sergio Carmona, Instituto de Neurociencias de Buenos Aires – INEBA, Argentina
Reviewed by:Marianne Dieterich, Ludwig-Maximilians-University, Germany
Copyright: © 2014 Ward, Roberts, Della Santina, Carey and Zee. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
*Correspondence: Bryan K. Ward, Department of Otolaryngology – Head and Neck Surgery, Johns Hopkins University School of Medicine, 601 North Caroline Street, 6th Floor, Baltimore, MD 21287-0910, USA e-mail: firstname.lastname@example.org