Cortical correlates of gesture processing: Clues to the cerebral mechanisms underlying apraxia during the imitation of meaningless gestures

The clinical test of imitation of meaningless gestures is highly sensitive in revealing limb apraxia after dominant left brain damage. To relate lesio n locations in apraxic patients to functional brain activation and to revea l the neuronal network subserving gesture: representation, repeated measure ments were made in seven healthy subjects during a gesture discrimination t ask. Observing paired images of either meaningless hand or meaningless fing er gestures, subjects had to indicate whether they were identical or differ ent. As a control condition subjects simply had to indicate whether two por trayed persons were identical or not. Brain activity during the discriminat ion of hand gestures was strongly lateralized to the left hemisphere, a pro minent peak activation being localized within the inferior parietal cortex (BA40). The discrimination of finger gestures induced a more symmetrical ac tivation and rCBF peaks in the right intraparietal sulcus and in medial vis ual association areas (BA18/19). Two additional foci of prominent rCBF incr ease were found. One focus was located at the left lateral occipitotemporal junction (BA 19/37) and was related to both tasks; the other in the pre-SM A was particularly related to hand gestures. The pattern of task-dependent activation corresponds closely to the predictions made from the clinical fi ndings, and underlines the left brain dominance for meaningless hand gestur es and the critical involvement of the parietal cortex. The lateral visual association areas appear to support first stages of gesture representation, and the parietal cortex is part of the dorsal action stream. Finger gestur es may require in addition precise visual analysis and spatial attention en abled by occipital and right intraparietal activity. Pre-SIMA activity duri ng the perception of hand gestures may reflect engagement of a network, tha t is intimately related to gesture execution. (C) 2001 Academic Press.