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Lateralization of language to the left hemisphere is considered a key aspect of human brain organization. We used diffusion tensor MRI to perform in vivo virtual dissection of language pathways to assess the relationship between brain asymmetry and cognitive performance in the normal population. Our findings suggest interhemispheric differences in direct connections between Broca's and Wernicke's territories, with extreme leftward lateralization in more than half of the subjects and bilateral symmetrical distribution in only 17.5% of the subjects. Importantly, individuals with more symmetric patterns of connections are better overall at remembering words using semantic association. Moreover, preliminary analysis suggests females are more likely to have a symmetrical pattern of connections. These findings suggest that the degree of lateralization of perisylvian pathways is heterogeneous in the normal population and, paradoxically, bilateral representation, not extreme lateralization, might ultimately be advantageous for specific cognitive functions.

Original publication

DOI

10.1073/pnas.0702116104

Type

Journal article

Journal

Proc Natl Acad Sci U S A

Publication Date

23/10/2007

Volume

104

Pages

17163 - 17168

Keywords

Adult, Brain, Brain Mapping, Female, Functional Laterality, Humans, Language, Male, Mental Recall, Sex Characteristics, Verbal Behavior