Crossed aphasia and related anomalies of cerebral organization: case reports and a genetic hypothesis.

Anomalous lateralization of cognitive functions is observed in a small percentage of right-handed patients with unilateral brain damage, either crossed aphasia (aphasia after right brain damage) or "crossed nonaphasia" (left brain damage without aphasia but with visuospatial and other deficits typical of right brain damage). No comprehensive theory of these anomalous cases has been proposed. Nine new right-handed cases (plus one left-handed case) were analyzed and the literature was reviewed. The dramatically anomalous organization of cognitive functions is best explained by random lateralization of all cognitive functions in a small subset of the population. The RS theory of cerebral dominance can account for this pattern of anomalies in right-handers and may account for the most common patterns of dominance observed in left-handers.