An examination of the effects of stimulus type, encoding task, and functional connectivity on the role of right...

Right anterior prefrontal cortex and other brain areas are active during memory retrieval but the role of prefrontal cortex and how it interacts with these other regions to mediate memory function remain unclear. To explore these issues we used positron emission tomography to examine the effects of stimulus material and encoding task on brain activity during visual recognition, assessing both task-related changes and functional connectivity. Words and pictures of objects were encoded using perceptual and semantic strategies, resulting in better memory for semantically encoded items. There was no significant effect of prior encoding strategy on brain activity during recognition. Right anterior prefrontal cortex was equally active during recognition of both types of stimuli irrespective of initial encoding strategy. Regions whose activity was positively correlated with activity in right anterior prefrontal cortex included widespread areas of prefrontal and inferior temporal cortices bilaterally. Activity in this entire network of regions was negatively correlated with recognition accuracy of semantically encoded items. These results suggest that initial encoding task has little impact on the set of brain regions that is active during subsequent recognition. Right anterior prefrontal cortex appears to be involved in retrieval mode, reflected in its equivalent activity across conditions differing in both stimulus type and encoding task, and also in retrieval effort, shown by the negative correlation between its functional connectivity and individual differences in recognition accuracy.