Article

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.
CI - Copyright (c) 2011 Elsevier Ltd. All rights reserved.

Langue : ANGLAIS