Effects of generation mode in fMRI adaptations of semantic fluency: Paced production and overt speech

Abstract

Verbal fluency is a widely used neuropsychological paradigm. In fMRI implementations, conventional unpaced (self-paced) versions are suboptimal due to uncontrolled timing of responses, and overt responses carry the risk of motion artifact. We investigated the behavioral and neurofunctional effects of response pacing and overt speech in semantic category-driven word generation. Twelve right-handed adults (8 female) ages 21-37 were scanned in four conditions each: Paced-Overt, Paced-Covert, Unpaced-Overt, and Unpaced-Covert. There was no significant difference in the number of exemplars generated between overt versions of the paced and unpaced conditions. Imaging results for category-driven word generation overall showed left-hemispheric activation in inferior frontal cortex, premotor cortex, cingulate gyrus, thalamus, and basal ganglia. Direct comparison of generation modes revealed significantly greater activation for the paced compared to unpaced conditions in right superior temporal, bilateral middle frontal, and bilateral anterior cingulate cortex, including regions associated with sustained attention, motor planning, and response inhibition. Covert (compared to overt) conditions showed significantly greater effects in right parietal and anterior cingulate, as well as left middle temporal and superior frontal regions. We conclude that paced overt paradigms are useful adaptations of conventional semantic fluency in fMRI, given their superiority with regard to control over and monitoring of behavioral responses. However, response pacing is associated with additional non-linguistic effects related to response inhibition, motor preparation, and sustained attention.

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“…In line with previous findings, 35,36 the healthy controls exhibited a typical activation pattern of paced overt verbal fluency task: areas related to category-driven word generation (left inferior and middle frontal cortex, the superior and middle temporal regions, left thalamus and lentiform nucleus), areas associated with paced response and overt articulation (cingulate cortex, right superior parietal cortex, insular cortex, thalamus, lentiform nucleus and cerebellum; see supplemental Figure S1 and Table S1 for details). These clusters were chosen as a priori ROIs for subsequent analyses.…”

“…We adopted the verbal fluency paradigm described by Basho and colleagues 35 to test language function. This fMRI task was chosen because it allows an appropriate response monitoring and a tight control over and reduced individual variability of task performance, making it suitable for the application in patients with cognitive deficits.…”

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