Institute of Psychiatry, King's College London, UK.
Neuropsychologia. 2011 Dec;49(14):3946-55. doi: 10.1016/j.neuropsychologia.2011.10.011. Epub 2011 Oct 17.
Right-hemisphere stroke can lead to the somatoparaphrenic delusion that parts of one's own body belong to someone else. To our knowledge, no previous study has experimentally assessed the sense of body part ownership in somatoparaphrenic patients when they see the body from a third-person perspective, as in a mirror. In alternating trials, we provided either direct first-person perspective vision of the arms, or indirect third-person perspective vision via a mirror in the frontal plane. We tested body ownership in these conditions in five patients with right-hemisphere lesions with left hemiplegia and neglect, including two patients with this somatoparaphrenic delusion. The somatoparaphrenic patients systematically attributed the ownership of their left plegic hands to someone else in direct view, but showed a statistically significant increase in ownership of the left hand in mirror view trials, as compared with the three control patients. Depending on the view offered (mirror or direct), judgements of ownership and disownership of the same limb could alternate within a few seconds. The patients did not particularly remark on these dramatic and repeated alterations between ownership and disownership. Conditions of direct- and mirror-view with simultaneous touch of the hand by the experimenter showed the same patterns of results as conditions without touch. This study provides the first experimental evidence that limb disownership can be altered using self-observation in a mirror, and in turn suggests dissociation between first- and third-person visual perspectives on the body. Furthermore, the fact that reinstatement of ownership by third-person perspective did not permanently abolish somatoparaphrenia suggests that the subjective sense of body ownership remained dominated by an impaired first-person representation of the body that could not be updated, nor integrated with other signals. More generally, our findings suggest that a neural network involving the perisylvian areas of the right hemisphere may be necessary for the integration of multiple representations of one's body and for a higher order re-representation of various bodily signals into a first-person sense of body ownership. We suggest that other areas, possibly including the occipital cortex, may be involved in the recognition of the body from a third-person visual perspective. We thus propose that somatoparaphrenia can be regarded as a neurogenic dissociation between the 'subjectively felt' and 'objectively seen' body. This recalls the developmental finding that young infants cannot link their 'felt body' with the view of themselves in a mirror.
右脑卒中可导致体像障碍，使患者产生错觉，认为自己身体的某些部分属于他人。据我们所知，之前尚无研究从第三人称视角（如镜子中）评估体像障碍患者对自身身体部位的拥有感。在交替试验中，我们分别直接给予患者第一人称视角的手臂视觉刺激，或通过正面放置的镜子给予间接的第三人称视角视觉刺激。我们在五项右侧大脑损伤伴左侧偏瘫和忽视的患者中测试了这些条件下的身体拥有感，其中包括两名患有这种体像障碍的患者。在直接观察中，这些体像障碍患者系统地将他们左侧偏瘫手的所有权归因于他人，但在镜子观察试验中，他们对左手的所有权明显增加，与三名对照患者相比。取决于提供的视图（镜子或直接），在几秒钟内可以交替出现对同一肢体的拥有和不拥有的判断。患者并没有特别注意到这些在拥有和不拥有之间的戏剧性和反复变化。直接观察和镜子观察条件下，同时由实验者触摸手的条件，与没有触摸的条件下表现出相同的结果模式。这项研究首次提供了实验证据，表明通过自我观察镜子中的身体，可以改变肢体的不拥有感，这反过来表明身体的第一人称和第三人称视觉视角之间存在分离。此外，通过第三人称视角重新获得所有权并没有永久消除体像障碍，这表明身体拥有感的主观感觉仍然由受损的第一人称身体表示主导，这种表示无法更新，也无法与其他信号整合。更一般地说，我们的发现表明，涉及右大脑外侧裂周围区域的神经网络可能是整合身体的多个表示以及将各种身体信号重新表示为第一人称身体拥有感所必需的。我们认为，其他区域，可能包括枕叶皮层，可能参与从第三人称视觉角度识别身体。因此，我们提出体像障碍可以被视为身体的“主观感觉”和“客观看到”之间的神经源性分离。这让人想起了发展心理学中的发现，即幼儿无法将自己的“感觉身体”与镜子中的自己的视图联系起来。
