MANIBUS Lab, Psychology Department, University of Turin, Italy.
Donders Institute for Brain, Cognition and Behaviour, Radboud University, the Netherlands.
Cortex. 2022 Aug;153:207-219. doi: 10.1016/j.cortex.2022.05.005. Epub 2022 May 24.
To investigate the relationship between the sense of body ownership and motor control, we capitalized on a rare bizarre disorder wherein another person's hand is misattributed to their own body, i.e., a pathological form of embodiment (E+). Importantly, despite E+ is usually associated with motor deficits, we had the opportunity to test two E+ patients with spared motor function, thus able to perform a reaching task. Crucially, these patients had proprioceptive deafferentation, allowing us to purely isolate the embodiment-dependent effect from proprioception-dependent ones that are usually associated in experimental manipulations of body ownership in healthy participants. Previous evidence suggests that the reaching movement vector is attracted towards an embodied hand during the rubber hand illusion (RHI). However, these results are confounded by the spared proprioception, whose modulation alone could explain the effects on reach planning. The neuropsychological approach employed here provides unambiguous evidence about the role of body ownership in reach planning. Indeed, three brain-damaged patients with proprioceptive deafferentation, two E+ and a well-matched control patient without pathological embodiment (E-), and 10 age-matched healthy controls underwent a reaching task wherein they had to reach for a target from a fixed starting point, while an alien hand (the co-experimenter's) was placed on the table. Irrespective of proprioception, damaged in all patients, only in E+ patients reaching errors were significantly more shifted consistently with the pathological belief, i.e., as if they planned movements from the position of the alien (embodied) hand, as compared to controls. Furthermore, with an additional experiment on healthy participants, we demonstrated that reaching errors observed during the RHI correlate with the changes in ownership. In conclusion, our neuropsychological approach suggests that when planning a reach, we do so from where our owned hand is and not from its physical location.
为了研究身体所有权和运动控制之间的关系，我们利用了一种罕见的奇异障碍，即他人的手被错误地归因于自己的身体，即一种病理性的体现形式（E+）。重要的是，尽管 E+通常与运动缺陷有关，但我们有机会测试两名运动功能未受损的 E+患者，从而能够执行伸手任务。至关重要的是，这些患者存在本体感觉传入缺失，使我们能够纯粹从本体感觉依赖的影响中分离出与健康参与者进行身体所有权实验操作通常相关的体现依赖性影响。先前的证据表明，在橡胶手错觉（RHI）中，伸手运动向量会被吸引到体现的手上。然而，这些结果受到保留的本体感觉的影响，单独对其进行调节就可以解释对伸手计划的影响。这里采用的神经心理学方法提供了明确的证据，证明了身体所有权在伸手计划中的作用。实际上，三名患有本体感觉传入缺失的脑损伤患者、两名 E+患者和一名无病理性体现的匹配对照组患者（E-）以及 10 名年龄匹配的健康对照组参与者进行了伸手任务，他们必须从固定起点伸手去够目标，同时将一个陌生的手（实验者的手）放在桌子上。无论本体感觉如何，所有患者都受损，只有在 E+患者中，伸手错误明显更偏向于病理性信念，即好像他们从陌生（体现的）手的位置计划动作，与对照组相比。此外，通过对健康参与者进行额外的实验，我们证明了在 RHI 期间观察到的伸手错误与所有权的变化相关。总之，我们的神经心理学方法表明，在计划伸手时，我们是从自己拥有的手的位置而不是从其物理位置进行计划。
