Recognition of self-produced movement in a case of severe neglect

We report the case of a 50-year-old man (Mr PA) who sustained a right thalamic-temporo-parietal lesion resulting in severe hemispatial neglect and somatoparaphrenic delusions in the acute phase. One month after the lesion, Mr PA's ability to recognize his own movements was systematically analysed by means of an apparatus which allowed either the patient's or the examiner's moving hand to be displayed on a single screen. When viewing the examiner's hand, the patient saw a movement which was either identical (congruent condition) or different from his own (incongruent condition). In the latter conditions, both the examiner's and the patient's hand movements were synchronized in order to have the best match in both space and time. Since both hands were covered with identical gloves, attribution judgements could be produced only by comparing an internal representation of the executed movement to the visual image presented on the screen. When moving his contralesional hand, Mr PA systematically denied being the owner of the hand displayed on the screen, regardless of whether it was his own or the examiner's. Attribution errors were very frequent, and denial of ownership was associated with confabulatory behaviour. The behaviour of Mr PA was compared to that of four normal subjects and two neglect patients. In neither group did subjects present feeling of non-belonging towards their own hand, or confabulatory behaviour. In agreement with previous reports relating abnormal activity in the right parietal cortex and misattribution of the source of an action, we suggest that the behaviour of Mr PA is a consequence of a disorder of body awareness. More precisely, we propose that in the present case, the body-reference system was defective, thus inducing the patient to refuse ownership of the hand presented on the screen, even when it was actually his own.