Functional magnetic resonance imaging of human brain activity ina verbal fluency task

OBJECTIVES—Functional MRI (fMRI) holds the promiseof non-invasive mapping of human brain function in both health anddisease. Yet its sensitivity and reliability for mapping highercognitive function are still being determined. Using verbal fluency asa task, the objective was to ascertain the consistency of fMRI on aconventional scanner for determining the anatomic substrate of languagebetween subjects and between sexes. Comparison was made with previous PET studies.
METHODS—Using a 1.5 Tesla magnet and an echoplanarpulse sequence, whole brain fMRI was obtained from 12 normal righthanded subjects (6 males and 6 females) as they performed a verbalfluency task.
RESULTS—A broadly consistent pattern of responsewas seen across subjects. Areas showing activation changes included theleft prefrontal cortex and right cerebellum, in agreement with previousPET ¹⁵O-H₂O studies. In addition, significantlydecreased responses were seen in the posterior cingulate and over anextensive area of mesial and dorsolateral parietal and superiortemporal cortices. The male cohort showed a slight asymmetry ofparietal deactivation, with more involvement on the right, whereas thefemale cohort showed a small region of activation in the rightorbitofrontal cortex. There were individual task related regionalchanges in all 12 subjects with the area showing the most significantchange being the left prefrontal cortex in all cases.
CONCLUSIONS—Magnetic resonance scanners ofconventional field strength can provide functional brain mapping datawith a sensitivity at least that of PET. Activation was seen in leftprefrontal and right cerebellar regions, as with PET. However,decremental responses were seen over a much larger area of theposterior cortex than had been anticipated by prior studies. Theability to see a response in each subject individually suggests thatfMRI may be useful in the preinterventional mapping of pathologicalstates, and offers a non-invasive alternative to the Wada test forassessment of hemispheric dominance. There were no gross differences inthe pattern of activation between male and female subjects.