The overall goal of this research is to understand the effects of large static magnetic fields, such as those encountered in an MRI machine, on brain function in general and the vestibular system in particular. This proposal follows anecdotal reports of subjects feeling dizzy near and in high strength MRI scanners and builds on an astounding discovery: All normal subjects develop a horizontal spontaneous nystagmus (drift of the eyes) when simply placed in the static field inside a 7 Tesla MRI machine, without any images being taken. This magnetic field-induced nystagmus likely reflects a vestibular imbalance induced by the effect of the magnetic field on the inner ear labyrinths. Previous research on MRI induced vertigo relied largely on subjective reports of dizziness and perception of movement. Using eye movements we have an objective, easily quantified way to investigate the effects of magnetic fields on brain function. Here we propose to investigate this phenomenon to understand its basic mechanism and relationship to labyrinthine function, and to derive the implications 1) for the diagnosis and potentially treatment of patients with brain diseases and especially those of the inner ear, 2) for neuroscientists who must interpret the changes in brain activity associated with different behavioral tasks during functional imaging studies, and.3) for the safety of human patients who undergo MRI scanning and for the health care workers who are exposed to magnetic fields. We first plan to discover whether induction of electric currents, flow of fluids within the semicircular canals, or the diamagnetic properties of labyrinthine structures, is the likely cause of the magnetic field induced nystagmus. Our strategy is to record eye movements using an infrared video system (to look for nystagmus in the dark so that subjects cannot fixate and suppress any induced nystagmus) and simultaneously the strength of the magnetic field as subjects are moved into and out of the bore at different speeds, in magnetic fields of different strength, for different durations in the MRI bore, and with the head in different orientations in the bore. To decipher the role of labyrinthine structures in this phenomenon we will see the pattern of MRI induced nystagmus in patients with different types of labyrinthine loss (e.g., unilateral vs. bilateral, partial vs. complete). We will use vestibular function tests performed away from the magnet including caloric and head rotational responses to assess the function of the semicircular canals, and ocular and cervical vestibular evoked myogenic potentials (VEMPs) to assess the otolith organs. These experiments address fundamental questions about the influence of magnetic fields on brain function. There will be important and potentially unsettling ramifications of the results of these experiments for many key areas of functional imaging research including cognition, motor control and perception. Finally, there are potentially important applications to medical diagnosis and treatment of vestibular disorders.