LATERALIZED HUMAN BRAIN LANGUAGE SYSTEMS DEMONSTRATED BY TASK SUBTRACTION FUNCTIONAL MAGNETIC-RESONANCE-IMAGING

Objective: To develop a procedure for noninvasive measurement of langu age lateralization with functional magnetic resonance imaging (MRI). D esign: Functional neuroimaging using time-series echo-planar MRI. Sett ing: University medical center research facility. Subjects: Five healt hy, right-handed, young adults. Main Outcome Measures: Number of MRI v oxels in left and right hemispheres showing task-related signal increa ses during two contrasting auditory processing tasks. The nonlinguisti c task involved processing of pure tones, while the linguistic task in volved processing of single words based on semantic content. Results: The pure-tone processing task activated temporal lobe auditory areas a nd dorsolateral frontal regions bilaterally. Using this task as a cont rol condition, the semantic processing task resulted in lateralized ac tivity in distributed regions of the left hemisphere. A significant ef fect of task on intrahemispheric activity pattern was demonstrated in every subject. Results were reproduced in preliminary studies of test- retest reliability. Conclusions: The results demonstrate the lateraliz ed anatomy of semantic linguistic systems in contrast to nonlinguistic auditory sensory processors and introduce a task subtraction techniqu e adapted for functional MRI as a noninvasive measure of language late ralization.