Evaluation of hemispheric dominance for language using functional MRI: a comparison with positron emission tomography

The utility of a conventional (i.e., nonecho-planar) functional magnetic resonance imaging (fMRI) technique to determine hemispheric dominance for language was assessed using a semantic generation task in which subjects were presented with a series of nouns and generated aloud a verb for each one. A direct comparison of the fMRI results with positron emission tomography (PET), acquired from the same subjects, was also performed. When analyzed by group averaging, the results of this work were in concordance with those of previous PET studies, showing a left hemispheric dominance for language. Analyzed on a individual basis, 7 out of 9 subjects were left-hemisphere dominant and 2 subjects were right-hemisphere dominant; this applied with both PeT and fMRI methods. The direct comparison between PET and fMRI further demonstrated that fMRI can replicate PET findings. Of the total activation foci detected by PeT, 92% were observed by fMRI. On the other hand, fMRI reported 64% more activations than did PET. This may reflect differences in procedure, spatial resolution, sensitivity, and the underlying physiological mechanism between PET and fMRI. This study suggests that the fMRI technique, even using conventional MRI scanners, could be clinically useful in evaluating hemispheric dominance for language on an individual subject-by-subject basis.