Buetler Karin A, Penalver-Andres Joaquin, Özen Özhan, Ferriroli Luca, Müri René M, Cazzoli Dario, Marchal-Crespo Laura
Motor Learning and Neurorehabilitation Laboratory, ARTORG Center for Biomedical Engineering Research, University of Bern, Bern, Switzerland.
Psychosomatic Medicine, Department of Neurology, University Hospital of Bern (Inselspital), Bern, Switzerland.
Front Hum Neurosci. 2022 Feb 9;15:787487. doi: 10.3389/fnhum.2021.787487. eCollection 2021.
To offer engaging neurorehabilitation training to neurologic patients, motor tasks are often visualized in virtual reality (VR). Recently introduced head-mounted displays (HMDs) allow to realistically mimic the body of the user from a first-person perspective (i.e., avatar) in a highly immersive VR environment. In this immersive environment, users may embody avatars with different body characteristics. Importantly, body characteristics impact how people perform actions. Therefore, alternating body perceptions using immersive VR may be a powerful tool to promote motor activity in neurologic patients. However, the ability of the brain to adapt motor commands based on a perceived modified reality has not yet been fully explored. To fill this gap, we "tricked the brain" using immersive VR and investigated if multisensory feedback modulating the physical properties of an embodied avatar influences motor brain networks and control. Ten healthy participants were immersed in a virtual environment using an HMD, where they saw an avatar from first-person perspective. We slowly transformed the surface of the avatar (i.e., the "skin material") from human to stone. We enforced this visual change by repetitively touching the real arm of the participant and the arm of the avatar with a (virtual) hammer, while progressively replacing the sound of the hammer against skin with stone hitting sound via loudspeaker. We applied single-pulse transcranial magnetic simulation (TMS) to evaluate changes in motor cortical excitability associated with the illusion. Further, to investigate if the "stone illusion" affected motor control, participants performed a reaching task with the human and stone avatar. Questionnaires assessed the subjectively reported strength of embodiment and illusion. Our results show that participants experienced the "stone arm illusion." Particularly, they rated their arm as heavier, colder, stiffer, and more insensitive when immersed with the stone than human avatar, without the illusion affecting their experienced feeling of body ownership. Further, the reported illusion strength was associated with enhanced motor cortical excitability and faster movement initiations, indicating that participants may have physically mirrored and compensated for the embodied body characteristics of the stone avatar. Together, immersive VR has the potential to influence motor brain networks by subtly modifying the perception of reality, opening new perspectives for the motor recovery of patients.
为了给神经科患者提供引人入胜的神经康复训练，运动任务通常在虚拟现实（VR）中进行可视化呈现。最近推出的头戴式显示器（HMD）能够在高度沉浸式的VR环境中从第一人称视角（即虚拟化身）逼真地模拟用户的身体。在这个沉浸式环境中，用户可以化身具有不同身体特征的虚拟角色。重要的是，身体特征会影响人们执行动作的方式。因此，使用沉浸式VR交替身体感知可能是促进神经科患者运动活动的有力工具。然而，大脑基于感知到的改变后的现实调整运动指令的能力尚未得到充分探索。为了填补这一空白，我们使用沉浸式VR“欺骗大脑”，并研究多感官反馈调节虚拟化身的物理属性是否会影响运动脑网络和控制。十名健康参与者使用HMD沉浸在虚拟环境中，在那里他们从第一人称视角看到一个虚拟化身。我们将虚拟化身的表面（即“皮肤材质”）从人类慢慢地转变为石头。我们通过用（虚拟）锤子反复触摸参与者的真实手臂和虚拟化身的手臂来强化这种视觉变化，同时通过扬声器逐渐用石头撞击的声音取代锤子敲击皮肤的声音。我们应用单脉冲经颅磁刺激（TMS）来评估与这种错觉相关的运动皮层兴奋性的变化。此外，为了研究“石头错觉”是否影响运动控制，参与者对人类和石头虚拟化身执行了伸手任务。问卷调查评估了主观报告的沉浸感和错觉强度。我们的结果表明，参与者体验到了“石头手臂错觉”。特别是，当他们沉浸在石头虚拟化身中时，他们将自己的手臂评定为比沉浸在人类虚拟化身中时更重、更冷、更僵硬且更不敏感，而这种错觉并未影响他们对身体所有权的体验感受。此外，报告的错觉强度与增强的运动皮层兴奋性和更快的运动启动相关，这表明参与者可能在身体上模仿并补偿了石头虚拟化身的身体特征。总之，沉浸式VR有潜力通过微妙地改变对现实的感知来影响运动脑网络，为患者的运动恢复开辟新的前景。
