Estimating Vestibular Perceptual Thresholds using a Six-Degree-of-Freedom Motion Platform.

Vestibular perceptual thresholds refer to the motion intensity required to enable a participant to detect or discriminate a motion based on vestibular input. Using passive motion profiles provided by six degree-of-motion platforms, vestibular perceptual thresholds can be estimated for any kind of motion and thereby target each of the sub-components of the vestibular end-organ. Assessments of vestibular thresholds are clinically relevant as they complement diagnostic tools such as caloric irrigation, the head impulse test (HIT), or vestibular evoked myogenic potentials (VEMPs), which only provide information on sub-components of the vestibular system, but none of them allow for assessing all components. There are several methods with different advantages and disadvantages for estimating vestibular perceptual thresholds. In this article, we present a protocol using an adaptive staircase algorithm and sinusoidal motion profiles for an efficient estimation procedure. Adaptive staircase algorithms consider the response history to determine the peak velocity of the next stimuli and are the most commonly used algorithms in the vestibular domain. We further discuss the impact of motion frequency on vestibular perceptual thresholds

Quantifying the influence of magnetic vestibular stimulation on spatial tasks

Strong magnetic fields induce dizziness, vertigo, and nystagmus due to Lorentz forces acting on the cupula in the semi-circular canals (Roberts et al. 2012). Studies using passive motion, galvanic or caloric vestibular stimulation have shown that vestibular information can interfere with cognitive tasks with spatial components (e.g., Falconer & Mast, 2012). In this study, we were interested if magnetic vestibular stimulation (MVS) in a 7 Tesla MRI scanner influences performance in cognitive tasks with spatial components. 30 participants solved a mental rotation task in a 7T MR scanner with an egocentric and an allocentric strategy. The findings of previous studies suggest that only the egocentric strategy should be affected by altered vestibular information. The allocentric strategy served as a control condition. The strength of MVS was manipulated within participants by letting them solve the task inside the bore with two different head positions, resulting in a stronger and a weaker stimulation condition (Wyssen et al., in press). Response time analyses showed that overall participants responded slower under stronger stimulation than under weaker stimulation. This effect of magnetic vestibular stimulation on response times was only present in the egocentric mental rotation task but not when participants used the allocentric strategy. However, participants showed inter-individual differences, and the strength of the individual effect could not be linked to the individual stimulation strength quantified by nystagmus. The findings of our study suggest that MVS could influence cognitive tasks with spatial components in MRI scanners. The effect of magnetic vestibular stimulation should be considered in fMRI studies using ultra-high magnetic fields using spatial tasks, as it could be a possible confounder. In the future magnet ic vestibular stimulation could serve as a tool to investigate the interrelation of vestibular information and spatial cognition. References: (1) Roberts, D. C., Marcelli, V., Gillen, J. S., Carey, J. P., Della Santina, C. C., & Zee, D. S. (2011). MRI magnetic field stimulates rotational sensors of the brain. Curr. Biol., 21(19), 1635-1640. (2) Falconer C. J., Mast F.W. (2012). Balancing the mind: vestibular induced facilitation of egocentric mental transformations. Exp. Psychol., 59(6):332-9. (3) Wyssen, G., Morrison, M., Korda, A., Wimmer, W., Otero-Millan, J., Ertl, M., Szukics, A.A., Wyss, T., Wagner, F., Caversaccio, M.D., Mantokoudis, G., Mast, F.W. (in press). Measuring the Influence of Magnetic Vestibular Stimulation on Nystagmus, Self-Motion Perception, and Cognitive Performance in a 7T MRT. J. Vis. Exp., e64022

Influence of magnetic vestibular stimulation on self-motion perception

Ultrahigh magnetic fields (UHF) induce dizziness, vertigo and nystagmus due to Lorentz forces acting on the cupula in the semi-circular canals, an effect called magnetic vestibular stimulation (MVS) (Roberts et al., 2011; Ward et al., 2015). As the effect of the magnetic field on the cupula remains constant throughout the exposure, MVS is specifically suitable for studying cognitive performance under vestibular stimulation. The effect of MVS can be set near to zero by tilting the head 30° forward towards the body, allowing to compare different strengths of MVS within subjects (Mian et al., 2016). Furthermore, MVS serves as a suitable non-invasive model for unilateral failure of the vestibular system, which enables studying compensatory processes (Ertl and Boegle, 2019). We conducted our study in a Siemens Terra 7 Tesla Scanner and tested 8 young, healthy participants and plan to include 30 more. The study had two main goals. First, to investigate the process of perception-reflex uncoupling, as under MVS self-motion perception differs from measured nystagmus in direction as well as time course. While horizontal nystagmus was predominant, most participants report a percept of roll rotation, and less frequent a percept of yaw rotation or a mixture of both when moving in to and out of the magnetic field. This matches previous studies (Mian et al., 2013). Reported percepts did not correspond fully to measured reflexive eye-movements. Overall, stronger nystagmus indicated stronger percepts. Roll percepts make sense because the brain integrates the prior knowledge and sensory evidence. In supine position, yaw but not roll rotation would also elicit change in direction of gravity. Second, to quantify influence of continuous vestibular stimulation on cognitive functions with spatial components. Behavioral and neuroimaging studies have shown repeatedly that caloric, galvanic and motion platform-induced vestibular stimulation can affect performance in spatial tasks, such as mental rotation (Klaus et al., 2019; Falconer & Mast, 2012). The influence of MVS on spatial cognition is relevant for fMRI studies as MVS can be a confounder, especially in studies using UHFs. In our study, we did not find a meaningful effect of MVS on mental body rotation performance, neither in allocentric nor in egocentric strategy. In the future, we aim to compare healthy participants and patients with vestibular disorders to investigate adaption and habituation mechanisms

Hippocampal volume in patients with bilateral and unilateral peripheral vestibular dysfunction.

Previous studies have found that peripheral vestibular dysfunction is associated with altered volumes in different brain structures, especially in the hippocampus. However, published evidence is conflicting. Based on previous findings, we compared hippocampal volume, as well as supramarginal, superior temporal, and postcentral gyrus in a sample of 55 patients with different conditions of peripheral vestibular dysfunction (bilateral, chronic unilateral, acute unilateral) to 39 age- and sex-matched healthy controls. In addition, we explored deviations in gray-matter volumes in hippocampal subfields. We also analysed correlations between morphometric data and visuo-spatial performance. Patients with vestibular dysfunction did not differ in total hippocampal volume from healthy controls. However, a reduced volume in the right presubiculum of the hippocampus and the left supramarginal gyrus was observed in patients with chronic and acute unilateral vestibular dysfunction, but not in patients with bilateral vestibular dysfunction. No association of altered volumes with visuo-spatial performance was found. An asymmetric vestibular input due to unilateral vestibular dysfunction might lead to reduced central brain volumes that are involved in vestibular processing

Measuring the Influence of Magnetic Vestibular Stimulation on Nystagmus, Self-Motion Perception, and Cognitive Performance in a 7T MRT.

Strong magnetic fields induce dizziness, vertigo, and nystagmus due to Lorentz forces acting on the cupula in the semi-circular canals, an effect called magnetic vestibular stimulation (MVS). In this article, we present an experimental setup in a 7T MRT scanner (MRI scanner) that allows the investigation of the influence of strong magnetic fields on nystagmus as well as perceptual and cognitive responses. The strength of MVS is manipulated by altering the head positions of the participants. The orientation of the participants' semicircular canals with respect to the static magnetic field is assessed by combining a 3D magnetometer and 3D constructive interference in steady-state (3D-CISS) images. This approach allows to account for intra- and inter-individual differences in participants' responses to MVS. In the future, MVS can be useful for clinical research, for example, in the investigation of compensatory processes in vestibular disorders. Furthermore, it could foster insights into the interplay between vestibular information and cognitive processes in terms of spatial cognition and the emergence of self-motion percepts under conflicting sensory information. In fMRI studies, MVS can elicit a possible confounding effect, especially in tasks influenced by vestibular information or in studies comparing vestibular patients with healthy controls

Measuring the influence of magnetic vestibular stimulation on nystamus, self-motion perception, and cognitive performance in a 7T MRT

This repository contains ressources for measuring effects of magnetic vestibular stimulation (MVS)

PlatformCommander — An open source software for an easy integration of motion platforms in research laboratories

Motion platforms are used to study human behavior and brain function during passive motions. The software for controlling motion platforms is typically developed by the respective laboratories. Such customized, closed source solutions make replications of studies or multi-center collaborations difficult. Therefore, we developed PlatformCommander, an open-source software package for interfacing two often used motion platform models (6DOF2000E., MB-E-6DOF). The software includes a server implementing the interaction with the motion platform and additional devices, and a client application, connecting to the server and controlling experiments. PlatformCommander is ideal for the synchronization of data from different sources with high temporal precision