Highly read on www.cell.com 25 Sept–25 Oct

The vertigo that many people experience when near or inside magnetic resonance imaging (MRI) machines may be due to a direct effect of the strong magnetic field on the fluid in the inner ear.

The labyrinth of the inner ear controls balance and consists of semicircular canals filled with ionic fluid. Dale Roberts at Johns Hopkins University in Baltimore, Maryland, and his colleagues placed ten healthy volunteers and two patients with dysfunctional labyrinths into MRI scanners, and exposed them to a static magnetic field. The healthy people — but not those with damaged labyrinths — continuously flicked their eyes sideways, as if to correct for perceived head movements. The pattern of eye movement depended on the polarity of the magnetic field and the orientation of the head.

The authors say that their data can best be explained by the action of a particular magnetic force, the Lorentz force, on the potassium-ion-rich labyrinth fluid. This force pushes the fluid against pressure sensors to bring about the sensation of vertigo.

Curr. Biol. 21, 1635–1640 (2011)