The role of the prefrontal cortex in recognition memory and memory for source: An fMRI study

We employed fLMRI to index neural activity in prefrontal cortex during test s of recognition and source memory. At study, subjects were presented with words displayed either to the left or right of fixation, and, depending on the side, performed one of two orienting tasks. The test phase consisted of a sequence of three 10-word blocks, displayed in central vision. For one b lock, subjects performed recognition judgements on a mixture of two old and eight, new words (low density recognition). For another block, recognition judgements were performed on a mixture of eight old and two new words (hig h density recognition). In the remaining block, also consisting of eight ol d and two new items, the requirement was to judge whether each word had bee n presented at study an the left or the right. Relative to the low density condition, high density recognition was associated with increased activity in right and, to a lesser extent, left, anterior prefrontal cortex (BA 10), replicating the findings of two previous PET studies. Right anterior prefr ontal activity did not show any further increase during the source task. In stead, greater activity was found, relative to high density recognition, in left RA 10, left inferior frontal gyrus (BA 45/47), and bilateral opercula r cortices (EA 45/47). The findings are inconsistent with the proposal that activation of right anterior prefrontal cortex during memory retrieval ref lects "postretrieval" processing demands, such demands being considerably g reater for judgments of source than recognition. The findings provide furth er evidence that the left prefrontal cortex plays a role in episodic memory retrieval when the task explicitly requires recovery of contextual as well as item information.