Perception of self-generated movement following left parietal lesion

Three apraxic patients with lesions in the left parietal cortex were requir ed to execute finger movements with either hand, while the visual feedback they received about the movement was manipulated systematically. We used a device which allowed us to present on a video monitor either the patient's hand or the examiner's hand simultaneously performing an identical or a dif ferent movement. In each trial, patients were required to decide whether th e hand shown on the screen was their own or not. Hand movements produced in response to verbal command included simple (single-finger extension) and c omplex gestures (multi-finger extension). Ownership judgements were analyse d and compared with those produced by six normal controls and two non-aprax ic neurological patients. Apraxic patients and controls accurately recogniz ed their own hand on the screen (own movement condition) and correctly iden tified the viewed hand as the examiner's when it performed a movement diffe rent from their own movement (incongruent movement condition). However, whe n the viewed hand was the examiner's hand executing their own movement (con gruent movement condition), apraxic patients were significantly more impair ed than controls. When the results were analysed as a function of gesture t ype, the number of correct responses was significantly lower for apraxic pa tients with respect to controls only for complex gestures. Interestingly, w hen patients executed the finger gestures inaccurately, they still failed t o recognize the examiner's hand as alien, and claimed that the correct move ment presented on the screen was their own. These results confirm that pari etal lesions alter the representational aspects of gestures, and suggest a failure in evaluating and comparing internal and external feedback about mo vement. We conclude that the parietal cortex plays an important role in gen erating and maintaining a kinaesthetic model of ongoing movements.