Magnetic Vestibular Stimulation (MVS) As a Technique for Understanding the Normal and Diseased Labyrinth

Abstract

Humans often experience dizziness and vertigo around strong static magnetic fields such as those present in an MRI scanner. Recent evidence supports the idea that this effect is the result of inner ear vestibular stimulation and that the mechanism is a magnetohydrodynamic force (Lorentz force) that is generated by the interactions between normal ionic currents in the inner ear endolymph and the strong static magnetic field of MRI machines. While in the MRI, the Lorentz force displaces the cupula of the lateral and anterior semicircular canals, as if the head was rotating with a constant acceleration. If a human subject’s eye movements are recorded when they are in darkness in an MRI machine (i.e., without fixation), there is a persistent nystagmus that diminishes but does not completely disappear over time. When the person exits the magnetic field, there is a transient aftereffect (nystagmus beating in the opposite direction) that reflects adaptation that occurred in the MRI. This magnetic vestibular stimulation (MVS) is a useful technique for exploring set-point adaptation, the process by which the brain adapts to a change in its environment, which in this case is vestibular imbalance. Here, we review the mechanism of MVS, how MVS produces a unique stimulus to the labyrinth that allows us to explore set-point adaptation, and how this technique might apply to the understanding and treatment of vestibular and other neurological disorders.

Classification of vestibular signs and examination techniques: Nystagmus and nystagmus-like movements

“…Comment: A strong static magnetic field, such as within an MRI scanner, induces nystagmus in subjects with normal vestibular function that is proportional to the magnetic field strength and whose direction is dependent on magnetic field polarity and head orientation. This nystagmus has been attributed to Lorentz forces from interaction between the magnetic field and naturally occurring ionic currents in the endolymph fluid acting to push the semicircular canal cupula to a new position [81,133,160].…”

Mouse Magnetic-field Nystagmus in Strong Static Magnetic Fields Is Dependent on the Presence of Nox3

“…In the inner ear a Lorentz force, engendered by both a strong static magnetic field and current entering utricular hair cells, is believed to create a force that acts on the endolymph above the utricle, causing semicircular canal cupular deflection and consequently, an observable nystagmus. This phenomenon has subsequently been corroborated in humans by other groups, and models have predicted that in strong MRI machines the forces are sufficient to deflect the cupulae 3–5 . Built upon both assessments of nystagmus direction in humans with functioning and diseased labyrinths and models of hair cell currents, the present theory of magnetic vestibular stimulation (MVS) is that the stimulated labyrinthine structures are the lateral and superior semicircular canals 6–8 , and that the utricle is the primary current source 1,4 .…”

Review of Audiovestibular Symptoms Following Exposure to Acoustic and Electromagnetic Energy Outside Conventional Human Hearing

“…Subsequently, Roberts et al systematically studied nystagmus in humans exposed to 7T MRI and proposed that a Lorentz force occurs in the labyrinth of healthy humans in an MRI, generated by the interactions of the strong static magnetic field and natural electric currents entering hair cells of the utricle (141). To date, this hypothesis explains the vertigo and nystagmus experienced by humans, rats and mice in magnetic fields (142). Importantly, this effect occurred due to the static magnetic field alone and not from radiofrequency pulses or time-varying magnetic fields.…”