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Submission + - MRI Magnets Cause Nystagmus (jhu.edu)

tibit writes: "In an interesting twist on "it's so old it's new again", Johns Hopkins researchers led by Dale Roberts found what must have been causing much confusion for doctors the world over: strong external magnetic field can stimulate the semicircular canals, causing vertigo and nystagmus (pendular eye motion). It's a textbook case of Lorentz force in action: our angular rate gyros, the semicircular canals in the middle ear, filled with endolymph, have a ionic current flowing across. In magnetic field, the current produces a force that pushes the lymph along the channel, causing stimulation of the cupula — a pressure sensor at the end of the channel. This is interpreted by the brain as rotation of head in space, and causes a nystagmus that's supposed to stabilize the image on the retina. Of course the subject is laying down and not spinning in space, and the mismatch between inertial measurements coming from the ear and real situation causes vertigo."

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