The meaning of meaningless gestures: a study of visuo-imitative apraxia.

In two patients with damage to the inferior portion of the left angular gyrus severely defective imitation of meaningless gestures contrasted with preserved performance of meaningful gestures to verbal command and with preserved imitation of meaningful gestures. In one patient the imitation deficit was restricted to the imitation of hand positions while imitation of finger configurations was normal. In both patients replication of the hand positions on a mannikin was as defective as imitation on themselves. This pattern of preserved and impaired performances is incompatible with two-stage models of apraxia which posit that defective imitation stems from damage to an executional stage of gesture production. Interruption of a direct route from perception to execution of action could account for the dissociation between defective imitation of meaningless and preserved performance of meaningful gestures. We propose that functioning of this route requires the integrity of general knowledge about the structure of the human body.