Sobell Department of Motor Neuroscience and Movement Disorders, Institute of Neurology, University College London, London, United Kingdom.
PLoS One. 2013 Oct 30;8(10):e78748. doi: 10.1371/journal.pone.0078748. eCollection 2013.
Vertigo is sometimes experienced in and around MRI scanners. Mechanisms involving stimulation of the vestibular system by movement in magnetic fields or magnetic field spatial gradients have been proposed. However, it was recently shown that vestibular-dependent ocular nystagmus is evoked when stationary in homogenous static magnetic fields. The proposed mechanism involves Lorentz forces acting on endolymph to deflect semicircular canal (SCC) cupulae. To investigate whether vertigo arises from a similar mechanism we recorded qualitative and quantitative aspects of vertigo and 2D eye movements from supine healthy adults (n = 25) deprived of vision while pushed into the 7T static field of an MRI scanner. Exposures were variable and included up to 135s stationary at 7T. Nystagmus was mainly horizontal, persisted during long-exposures with partial decline, and reversed upon withdrawal. The dominant vertiginous perception with the head facing up was rotation in the horizontal plane (85% incidence) with a consistent direction across participants. With the head turned 90 degrees in yaw the perception did not transform into equivalent vertical plane rotation, indicating a context-dependency of the perception. During long exposures, illusory rotation lasted on average 50 s, including 42 s whilst stationary at 7T. Upon withdrawal, perception re-emerged and reversed, lasting on average 30 s. Onset fields for nystagmus and perception were significantly correlated (p<.05). Although perception did not persist as long as nystagmus, this is a known feature of continuous SSC stimulation. These observations, and others in the paper, are compatible with magnetic-field evoked-vertigo and nystagmus sharing a common mechanism. With this interpretation, response decay and reversal upon withdrawal from the field, are due to adaptation to continuous vestibular input. Although the study does not entirely exclude the possibility of mechanisms involving transient vestibular stimulation during movement in and out of the bore, we argue these are less likely.
眩晕有时会在磁共振成像 (MRI) 扫描仪内外发生。人们提出了一些机制,涉及磁场或磁场空间梯度对前庭系统的刺激。然而,最近的研究表明,当处于均匀静磁场中静止时,会诱发依赖前庭的眼球性眼震。所提出的机制涉及作用在内淋巴上的洛伦兹力,使半规管(SCC)帽偏转。为了研究眩晕是否来自类似的机制,我们记录了 25 名仰卧健康成年人在被推入 MRI 扫描仪的 7T 静磁场时的眩晕的定性和定量方面以及 2D 眼球运动。暴露时间是可变的,包括在 7T 处最多 135s 的静止。眼震主要是水平的,在长时间暴露时持续存在,部分下降,撤出时反转。头部朝上时主要的眩晕感觉是在水平平面上旋转(85%的发生率),参与者的方向一致。当头向侧面转动 90 度时,感觉不会转变为等效的垂直平面旋转,表明感觉具有上下文依赖性。在长时间暴露时,错觉旋转持续平均 50s,包括在 7T 处静止时持续 42s。撤出时,感觉重新出现并反转,持续平均 30s。眼震和感觉的起始场显著相关(p<.05)。尽管感觉持续时间不如眼震长,但这是连续 SCC 刺激的已知特征。这些观察结果和本文中的其他结果与磁场诱发的眩晕和眼震具有共同机制是一致的。根据这种解释,当从磁场中撤出时,反应的衰减和反转是由于对连续前庭输入的适应。虽然该研究并没有完全排除在进出磁体时运动过程中短暂性前庭刺激的可能性,但我们认为这种可能性较小。