Recognition and imitation of pantomimed motor acts after unilateral parietal and premotor lesions: a perspective on apraxia.

We compared gesture comprehension and imitation in patients with lesions in the left parietal lobe (LPAR, n=5) and premotor cortex/supplementary motor area (LPMA, n=8) in patients with damage to the right parietal lobe (RPAR, n=6) and right premotor/supplementary motor area (RPMA, n=6) and in 16 non-brain damaged control subjects. Three patients with left parietal lobe damage had aphasia. Subjects were shown 136 meaningful pantomimed motor acts on a videoscreen and were asked to identify the movements and to imitate the motor acts from memory with their ipsilesional and contralesional hand or with both hands simultaneously. Motor tasks included gestures without object use (e.g. to salute, to wave) pantomimed imitation of gestures on one's own body (e.g. to comb one's hair) and pantomimed imitation of motor acts which imply tool use to an object in extrapersonal space (e.g. to hammer a nail). Videotaped test performance was analysed by two independent raters; errors were classified as spatial errors, body part as object, parapraxic performance and non-identifiable movements. In addition, action discrimination was tested by evaluating whether a complex motor sequence was correctly performed. Results indicate that LPAR patients were most severely disturbed when imitation performance was assessed. Interestingly, LPAR patients were worse when imitating gestures on their own bodies than imitating movements with reference to an external object use with most pronounced deficits in the spatial domain. In contrast to imitation, comprehension was not or only slightly disturbed and no clear correlation was found between the severity of imitation deficits and gesture comprehension. Moreover, although the three patients with aphasia imitated the movements more poorly than non-aphasic LPAR patients, the severity of comprehension errors did not differ. Whereas unimanual imitating performance and gesture comprehension of PMA patients did not differ significantly from control subjects, bimanual tasks were severely disturbed, in particular when executing different movements simultaneously with the right and left hands.