Functional magnetic resonance imaging (fMRI) is widely used to study brain activation with high spatial resolution. Recently, human studies have shown that the strong static magnetic field required for fMRI incidentally yields magnetic vestibular stimulation (MVS). These studies show that MVS: 1) is evoked by the static field, 2) does not require subject movement, and 3) does not depend upon magnetic field changes (e.g., dB/dt). These empirical findings suggest that magnetic vestibular stimulation (MVS) could affect a large number of fMRI studies, including resting state brain imaging, since MVS yields vestibular responses that vary with inner ear orientation relative to the magnetic field. Given the pervasive influence of vestibular stimuli - including influences on visual processing, cardiovascular regulation, equilibrium, and motion sickness - MVS could potentially contaminate a broad range of imaging studies. To address these concerns, we propose to develop a procedure to minimize the influences of MVS (Aim 1). Furthermore, once we can minimize the influences of MVS, we will also choose to employ MVS when desired (Aim 2). More specifically, our goal in Aim 1 is to develop a procedure to minimize the influence of MVS by measuring perception and nystagmus in a 7T magnet to find a range of head positions for each subject that yield no perceptible and minimal measurable MVS effects. To minimize the influence of variations in peripheral vestibular anatomy, we also propose to image the gross anatomy (e.g., semicircular canal orientation) of the vestibular periphery. To demonstrate that MVS impacts resting state activation and to demonstrate that we can minimize its influence, functional imaging will be performed with the head tilted into one of two positions - a position found to eliminate MVS-evoked perceptual illusions and minimize nystagmus and a second position that yields both perceptual illusions and nystagmus. After determining how to minimize MVS due to the static magnetic field in Aim 1, we propose to employ MVS evoked by the static magnetic field in Aim 2 to investigate why fMRI activation differs from normal for patients suffering from vestibular migraine (VM) - a disorder accompanied by abnormal processing of vestibular stimuli.
Functional magnetic resonance imaging (fMRI) is widely used to study human and animal brain activation. Recently, magnetic vestibular stimulation (MVS), which can affect images obtained via fMRI, has been discovered to occur in the strong magnets used to perform functional imaging. We propose to characterize this MVS in different head positions. Armed with this understanding, we plan to develop a procedure that will allow us both: (a) to employ MVS as a new form of controllable vestibular stimulation when desired and (b) to minimize MVS when we wish.
