Deficient sequencing of pantomimes in apraxia

Typically, the apraxic deficit of patients with left hemisphere damage is more pronounced for complex, i.e., sequential actions, than for simple ones. This impaired action sequencing can be attributed to a faulty selection of movements, a deficit of shifting motor attention, or, alternatively, disturbed processing of action-related temporal information.

Twenty patients with lesions of the left hemisphere with and without apraxia and 20 patients with right hemisphere lesions with and without neglect were asked to detect errors in the sequential structure or the spatial configuration of object-related complex actions, visually presented as actions with objects or pantomimes.

As expected, both patients with apraxia and neglect performed worse than patients without neuropsychological deficit (or elderly control subjects, n = 10). Side of lesion per se did not influence error rate. In contrast, left hemisphere-damaged patients with apraxia showed a specific deficit in detecting errors in the sequential structure of complex pantomime actions. In accordance with functional imaging studies showing an involvement of the left parietal cortex in movement-related temporal processing, lesion analysis of the patients with left hemisphere lesions revealed that damage to the inferior parietal cortex (angular gyrus) was associated with this specific impairment in detecting sequential errors in pantomime action.

The data suggest that impaired processing of temporal movement information due to lesions of the left inferior parietal cortex contributes to the complex action sequencing deficit in apraxia.