Comparison of brain activation during word retrieval done silently and aloud using fMRI

Using functional MRI we compared the patterns of activation in an effortful word retrieval task (stem completion) performed both silently and aloud. T he silent and overt conditions showed expected differences in activation ma gnitude in regions such as primary motor cortex. Some regions, such as fron tal operculum and dorsolateral frontal cortex, showed similar activation ma gnitude across conditions. Thalamus was more active on the left in both con ditions and showed a symmetric drop in activity in the silent compared with the overt condition. Putamen was also more active in the overt condition a nd showed a larger decrease in activity on the right than on the left in th e silent compared with the overt condition. Thus it appears that silent and overt performance of this task engage the thalamus and putamen in differen t ways. (C) 2000 Academic Press.