Pozeg Polona, Rognini Giulio, Salomon Roy, Blanke Olaf
Center for Neuroprosthetics, School of Life Science, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland; Laboratory of Cognitive Neuroscience, Brain Mind Institute, School of Life Science, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland.
Center for Neuroprosthetics, School of Life Science, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland; Laboratory of Cognitive Neuroscience, Brain Mind Institute, School of Life Science, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland; Robotic Systems Laboratory 1, Institute of Microengineering, School of Engineering, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland.
PLoS One. 2014 Apr 3;9(4):e94008. doi: 10.1371/journal.pone.0094008. eCollection 2014.
Manipulation of hand posture, such as crossing the hands, has been frequently used to study how the body and its immediately surrounding space are represented in the brain. Abundant data show that crossed arms posture impairs remapping of tactile stimuli from somatotopic to external space reference frame and deteriorates performance on several tactile processing tasks. Here we investigated how impaired tactile remapping affects the illusory self-touch, induced by the non-visual variant of the rubber hand illusion (RHI) paradigm. In this paradigm blindfolded participants (Experiment 1) had their hands either uncrossed or crossed over the body midline. The strength of illusory self-touch was measured with questionnaire ratings and proprioceptive drift. Our results showed that, during synchronous tactile stimulation, the strength of illusory self-touch increased when hands were crossed compared to the uncrossed posture. Follow-up experiments showed that the increase in illusion strength was not related to unfamiliar hand position (Experiment 2) and that it was equally strengthened regardless of where in the peripersonal space the hands were crossed (Experiment 3). However, while the boosting effect of crossing the hands was evident from subjective ratings, the proprioceptive drift was not modulated by crossed posture. Finally, in contrast to the illusion increase in the non-visual RHI, the crossed hand postures did not alter illusory ownership or proprioceptive drift in the classical, visuo-tactile version of RHI (Experiment 4). We argue that the increase in illusory self-touch is related to misalignment of somatotopic and external reference frames and consequently inadequate tactile-proprioceptive integration, leading to re-weighting of the tactile and proprioceptive signals.The present study not only shows that illusory self-touch can be induced by crossing the hands, but importantly, that this posture is associated with a stronger illusion.
手部姿势的操控，例如交叉双手，已被频繁用于研究身体及其紧邻空间在大脑中是如何被表征的。大量数据表明，交叉双臂姿势会损害触觉刺激从躯体感觉拓扑图到外部空间参考框架的重新映射，并降低多项触觉处理任务的表现。在此，我们研究了受损的触觉重新映射如何影响由橡皮手错觉（RHI）范式的非视觉变体诱发的错觉性自我触摸。在这个范式中，蒙眼的参与者（实验1）双手要么不交叉，要么交叉于身体中线之上。通过问卷评分和本体感觉漂移来测量错觉性自我触摸的强度。我们的结果表明，在同步触觉刺激期间，与双手不交叉的姿势相比，当双手交叉时，错觉性自我触摸的强度会增加。后续实验表明，错觉强度的增加与不熟悉的手部位置无关（实验2），并且无论双手在个人周边空间的何处交叉，错觉强度都会同样增强（实验3）。然而，虽然从主观评分中可以明显看出交叉双手的增强效果，但本体感觉漂移并未受到交叉姿势的调节。最后，与非视觉RHI中的错觉增加相反，交叉的手部姿势并未改变经典视觉触觉版本RHI中的错觉所有权或本体感觉漂移（实验4）。我们认为，错觉性自我触摸的增加与躯体感觉拓扑图和外部参考框架的错位有关，进而导致触觉 - 本体感觉整合不足，从而导致触觉和本体感觉信号的重新加权。本研究不仅表明交叉双手可以诱发错觉性自我触摸，而且重要的是，这种姿势与更强的错觉有关。
