Mian Omar S, Li Yan, Antunes Andre, Glover Paul M, Day Brian L
Sobell Department of Motor Neuroscience and Movement Disorders, Institute of Neurology, University College London, London, UK.
Sir Peter Mansfield Imaging Centre, University of Nottingham, Nottingham, UK.
J Physiol. 2016 Feb 15;594(4):1051-67. doi: 10.1113/JP271513. Epub 2015 Dec 30.
Lying supine in a strong magnetic field, such as in magnetic resonance imaging scanners, can induce a perception of whole-body rotation. The leading hypothesis to explain this invokes a Lorentz force mechanism acting on vestibular endolymph that acts to stimulate semicircular canals. The hypothesis predicts that the perception of whole-body rotation will depend on head orientation in the field. Results showed that the direction and magnitude of apparent whole-body rotation while stationary in a 7 T magnetic field is influenced by head orientation. The data are compatible with the Lorentz force hypothesis of magnetic vestibular stimulation and furthermore demonstrate the operation of a spatial transformation process from head-referenced vestibular signals to Earth-referenced body motion.
High strength static magnetic fields are known to induce vertigo, believed to be via stimulation of the vestibular system. The leading hypothesis (Lorentz forces) predicts that the induced vertigo should depend on the orientation of the magnetic field relative to the head. In this study we examined the effect of static head pitch (-80 to +40 deg; 12 participants) and roll (-40 to +40 deg; 11 participants) on qualitative and quantitative aspects of vertigo experienced in the dark by healthy humans when exposed to the static uniform magnetic field inside a 7 T MRI scanner. Three participants were additionally examined at 180 deg pitch and roll orientations. The effect of roll orientation on horizontal and vertical nystagmus was also measured and was found to affect only the vertical component. Vertigo was most discomforting when head pitch was around 60 deg extension and was mildest when it was around 20 deg flexion. Quantitative analysis of vertigo focused on the induced perception of horizontal-plane rotation reported online with the aid of hand-held switches. Head orientation had effects on both the magnitude and the direction of this perceived rotation. The data suggest sinusoidal relationships between head orientation and perception with spatial periods of 180 deg for pitch and 360 deg for roll, which we explain is consistent with the Lorentz force hypothesis. The effects of head pitch on vertigo and previously reported nystagmus are consistent with both effects being driven by a common vestibular signal. To explain all the observed effects, this common signal requires contributions from multiple semicircular canals.
仰卧于强磁场中，如在磁共振成像扫描仪内，可诱发全身旋转的感觉。解释这一现象的主流假说是，作用于前庭内淋巴的洛伦兹力机制会刺激半规管。该假说预测，全身旋转的感觉将取决于头部在磁场中的方向。结果表明，在7T磁场中静止时，明显的全身旋转方向和幅度受头部方向影响。这些数据与磁前庭刺激的洛伦兹力假说相符，并且进一步证明了从前庭信号到地球参考系身体运动的空间转换过程的运作。
已知高强度静磁场会诱发眩晕，据信是通过刺激前庭系统。主流假说（洛伦兹力）预测，诱发的眩晕应取决于磁场相对于头部的方向。在本研究中，我们研究了静态头部俯仰（-80至+40度；12名参与者）和横滚（-40至+40度；11名参与者）对健康人在7T磁共振成像扫描仪内的静磁场中于黑暗中所经历眩晕的定性和定量方面的影响。另外3名参与者在俯仰和横滚方向为180度时也接受了检查。还测量了横滚方向对水平和垂直眼球震颤的影响，发现其仅影响垂直分量。当头部俯仰约为60度伸展时，眩晕最不适，而在约20度屈曲时最轻微。眩晕的定量分析集中在借助手持开关在线报告的水平面旋转诱发感觉上。头部方向对这种感知旋转的幅度和方向均有影响。数据表明头部方向与感知之间呈正弦关系，俯仰的空间周期为180度，横滚为360度，我们解释这与洛伦兹力假说一致。头部俯仰对眩晕和先前报道的眼球震颤的影响与两者均由共同的前庭信号驱动一致。为了解释所有观察到的效应，这种共同信号需要多个半规管的贡献。
