身体所有感と一人称視点の自分の手

Neuropsychologia. 2011 Dec;49(14):3946-55. 

Mirror-view reverses somatoparaphrenia: dissociation between first- and third-person perspectives on body ownership.

Fotopoulou A1, Jenkinson PM, Tsakiris M, Haggard P, Rudd A, Kopelman MD.

• 1Institute of Psychiatry, King's College London, UK. a.fotopoulou@kcl.ac.uk

Abstract

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 inmirror 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.

右半球への脳損傷により、自己の身体が誰か他人の身体の一部のように感じる身体パラフレニアという症状を呈する事がある。身体パラフレニアの患者において自己の身体を鏡を通して三人称視点で見る事により、見ている自分の身体に対する所有感がどのように変化するかを実験的に調べた研究は、我々が知る限りない。そこで、身体パラフレニアの患者に、直接腕を見るという１人称視点または、鏡を通して腕を見るという３人称視点の２つの条件下を設けて、実験を行った。これらの２条件を、５名の右半球損傷患者（２名が身体パラフレニアを有する）に行い身体所有感を調べた。その結果、身体パラフレニア患者では、直接手を見る条件において左麻痺手の身体所有感が低く、他人の手のように感じるが、鏡を通して手を見る条件では、身体所有感が有意に上がり、自己の身体と感じていた。視点の違いによる所有感の有無は、数秒程度ですぐに変化が見られた。患者は、このドラマティックで繰り返される所有感の有無の変化に関してあまり注意を向けていなかった。また、人称視点を変化させると同時に実験者が麻痺手に触れることによる違いは生じなかった。この研究は、身体所有感の欠如は、鏡を用いて見る事により変化し、身体に関する１人称視点と３人称視点の身体が、それぞれ異なる処理を受けていることが示唆される。さらに、３人称視点による身体所有感の惹起が、永久的に身体パラフレニアを消失させない事は、主観的な身体所有感が、障害された身体の１人称称視点の表象により支配されている事が示唆される。

一人称視点で感じる所有感と三人称視点で感じる所有感が異なっている可能性があるんですかね〜。