Similar and dissociable mechanisms for attention to internal versus external information

We compared two attentional executive processes: updating, which involved attending to a perceptually present stimulus, and refreshing, which involved attending to a mentally active representation of a stimulus no longer perceptually present. In separate blocks, participants either replaced a word being held in working memory with a different word (update), or they thought back to a just previously seen word that was no longer perceptually present (refresh). Bilateral areas of frontal cortex, supplementary motor area, and parietal cortex were similarly active for both updating and refreshing, suggesting that a common network of areas is recruited to bring information to the current focus of attention. In a direct comparison of update and refresh, regions more active for update than refresh included regions primarily in right frontal cortex, as well as bilateral posterior visual processing regions. Regions more active for refresh than update included regions primarily in left dorsolateral frontal and left temporal cortex and bilateral inferior frontal cortex. These findings help account for the similarity in areas activated across different cognitive tasks and may help specify the particular executive processes engaged in more complex tasks.