Purpose Although both frontal and parietal cortices, particularly in the right hemisphere, are thought to be associated with visuospatial processing, the specific neuroanatomical sites essential for this ability are not well established. The purpose of this study was to more precisely identify the specific cortical regions that control visuospatial ability.
Methods The study included 67 normal control subjects, 33 stroke subjects with left hemisphere damage (LHD) and 24 stroke subjects with right hemisphere damage (RHD). Performance on the Block Design (BD) subtest of the Wechsler Adult Intelligence Scale (WAIS-R) was our measure of spatial ability. MRIs or CT scans were obtained on all stroke subjects and the specific brain area(s) damaged were traced into a computer program. Subjects were separated into six groups depending on whether the LHD or RHD was anterior (ant), posterior (post), or both anterior and posterior (ant-post) to the central sulcus. The areas of damage were overlapped separately depending on whether BD performance was normal or impaired (1 SD below the mean score of control subjects) and the lesion overlaps were compared to identify the specific brain regions most important for BD performance.
Results Subjects with ant, post, ant-post RHD or post LHD performed significantly worse than the control group; those with ant-post RHD scored lower than all other subjects in the study. Subjects with BD impairment were more likely to have damage of the left or right dorsolateral prefrontal and left parietal cortices than were subjects with normal BD performance. In contrast, subjects with BD impairment were not more likely to have damage to the right parietal cortex.
Conclusions Consistent with previous research highlighting the overall importance of the right hemisphere in spatial processing, we found that subjects with RHD performed worse on BD than those with LHD. Involvement of bilateral dorsolateral prefrontal cortices in BD performance agrees with the known importance of this area for spatial working memory and planning while involvement of the left parietal cortex supports previous work that emphasizes a role for this area in processing spatial details. However, lack of localization of visuospatial skill to the right inferior parietal cortex is inconsistent with the previous literature. This was the first study to couple MRI lesion localization with BD performance, but if replicated, these findings suggest that complex spatial processing is more diffusely controlled within the right hemisphere than the left hemisphere. Further investigation using more advanced imaging techniques, such as voxel-based lesion-symptoms mapping (VSLM), will allow for more precise cortical localization of visuospatial processing.
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