Cerebral lateralization of language in normal left-handed people studied by functional MRI

Objective: To use functional MRI (fMRI) to further define the occurrence of left-hemisphere, bilateral, and right-hemisphere language in a normal left-handed population. Methods: A total of 100 healthy volunteers, consisting of 50 left-handed subjects and a reference group of 50 right-handed subjects, were studied by fMRI of the frontal cortex during silent word generation. Results: Ninety-six percent of right-handed subjects showed fMRI changes lateralized to the left hemisphere, whereas 4% showed a bilateral activation pattern. In contrast, left-hemisphere lateralization occurred in 76% of left-handers, bilateral activation in 14%, and right-hemisphere lateralization in the remaining 10%. The predominance of right-hemisphere activation, however, was weak in these cases; only a single left-handed subject (2%) showed complete right-hemisphere lateralization. Conclusions: Silent word generation lateralizes to the left cerebral hemisphere in both handedness groups, but right-hemisphere participation is frequent in normal left-handed subjects. Exclusive right-hemisphere activation rarely occurred in the frontal lobe region studied.