Comparison of rhyming and word generation with FMRI

Functional magnetic resonance imaging (FMRI) has been successfully used to non-invasively map language function, but has several disadvantages. These include severe motion sensitivity, which limits overt verbal responses in b ehavioral paradigms, such as word generation. The lack of overt responses p revents behavioral validation, making data interpretation difficult. Our ob jective was to compare the FMRI activation patterns of a novel silent rhyme determination task requiring a non-verbal response, to covert word generat ion from visually presented letters. Five strongly right-handed subjects pe rformed both tasks during multi-slice coronal echo-planar T2*-weighted FMRI . Single subject activation maps were generated for each task by correlatio n analysis of single pixel time series to a boxcar reference function. Thes e maps for the two tasks were separately interpolated to 256(3), transforme d into Talairach space, summed, and thresholded at t>6. Combined activation maps from both tasks showed similar robust perisylvian language area activ ation, including inferior frontal gyrus, posterior superior temporal lobe, and fusiform gyrus. Subjects performed well on the rhyming task, which acti vated left hemisphere cortical regions more selectively than the word gener ation task. The rhyming task showed less activation than the word generatio n task in areas typically not considered specifically related to language f unction, such as the dorsolateral prefrontal cortex and anterior cingulate. The rhyming task is a useful tool for brain mapping and clinical applicati ons, potentially more specific to cortical language areas than verbal fluen cy. (C) 2000 Wiley-Liss, Inc.