OBJECTIVE: To develop a procedure for noninvasive measurement of
language lateralization with functional magnetic resonance imaging
(MRI). DESIGN: Functional neuroimaging using time-series echo-planar
MRI. SETTING: University medical center research facility. SUBJECTS:
Five healthy, right-handed, young adults. MAIN OUTCOME MEASURES:
Number of MRI voxels in left and right hemispheres showing
task-related signal increases during two contrasting auditory
processing tasks. The nonlinguistic task involved processing of pure
tones, while the linguistic task involved processing of single words
based on semantic content. RESULTS: The pure-tone processing task
activated temporal lobe auditory areas and dorsolateral frontal
regions bilaterally. Using this task as a control condition, the
semantic processing task resulted in lateralized activity in
distributed regions of the left hemisphere. A significant effect 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 lateralized
anatomy of semantic linguistic systems in contrast to non-linguistic
auditory sensory processors and introduce a task subtraction technique
adapted for functional MRI as a noninvasive measure of language
lateralization.