Relative shift in activity from medial to lateral frontal cortex during internally versus externally guided word generation

Goldberg (1985) hypothesized that as language output changes from internall y to externally guided production, activity shifts from supplementary motor area (SMA) to lateral premotor areas, including Broca's area. To test this hypothesis, 15 right-handed native English speakers performed three word g eneration tasks varying in the amount of internal guidance and a repetition task during functional magnetic resonance imaging (fMRI). Volumes of signi ficant activity for each task versus a resting state were derived using vox el-by-voxel repeated-measures t tests (p <.001) across subjects. Changes in the size of activity volumes for left medial frontal regions (SMA and pre- SMA/BA 32) versus left lateral frontal regions (Broca's area, inferior fron tal sulcus) were assessed as internal guidance of word generation decreased and external guidance increased. Comparing SMA to Broca's area, Goldberg's hypothesis was not verified. However, pre-SMA/BA 32 activity volumes decre ased significantly and inferior frontal sulcus activity volumes increased s ignificantly as word generation tasks moved from internally to externally g uided.