Motor impairment in patients with parietal lesions: disturbances of meaningless arm movement sequences

The execution of meaningless movement sequences was studied in 12 patients with lesions of the parietal cortex in comparison to the performance of age - and sex-matched controls. Five sequences of increasing complexity had to be performed by imitation and after verbal instruction. The performance err ors were qualitatively scored by means of four error categories (temporal o r spatial error, addition or omission of movement components). This study e xamined whether the error scores depended on instruction modality, movement complexity or lesion side. Patients with left parietal lesions produced mo re errors than those with right parietal lesions and control subjects. Whil e additions or omissions of movement components occurred almost equally in all groups, temporal and spatial errors were more frequent in patients with left parietal lesions only. In addition, only the latter group showed a si gnificant increase of error rates with increasing movement complexity. Ther e were no significant differences between the contra- and ipsilesional hand in any group. These results demonstrate that lesions in the left parietal lobe lead to a disturbed spatio-temporal organisation of movement that beco mes increasingly prominent for more complex movements. (C) 2001 Elsevier Sc ience Ltd. All rights reserved.