Imitating gestures and manipulating a mannikin--the representation of the human body in ideomotor apraxia.

Imitation of meaningless gestures was examined in patients with left brain damage (LBD), right brain damage (RBD) and controls. In addition to imitation on the own body, patients were asked to replicate the gestures on a life-sized mannikin. Manual dexterity was assessed by manipulation of beads, and general visuospatial abilities by block-design. LBD patients who displayed apraxia when imitating gestures on their own bodies scored dramatically worse than any other group when imitation was assessed on the mannikin. By contrast, on block-design and manipulation of beads patients with RBD were inferior not only to LBD patients without apraxia but also to apractic patients. Analysis of CT scans revealed that apraxia occurred with frontal, parietal and deep lesions, and that the impairment on the manipulation of the mannikin was present regardless of lesion site. The results support the contention that the basic deficit underlying impaired imitation of meaningless gestures in apraxia is to be sought at a conceptual level. Possibly, patients with apraxia are not able to evoke and represent conceptual knowledge about the human body which is necessary for performing the apparently simple task of imitating gestures.