Dissociating source memory decisions in prefrontal cortex: fMRI of diagnostic and disqualifying monitoring

■ We used event-related fMRI to study two types of retrieval monitoring that regulate episodic memory accuracy: diagnostic and disqualifying monitoring. Diagnostic monitoring relies on expectations, whereby the failure to retrieve expected recollec-tions prevents source memory misattributions (sometimes called the distinctiveness heuristic). Disqualifying monitoring relies on corroborative evidence, whereby the successful recollec-tion of accurate source information prevents misattribution to an alternative source (sometimes called recall to reject). Using criterial recollection tests, we found that orienting retrieval toward distinctive recollections (colored pictures) reduced source memory misattributions compared with a control test in which retrieval was oriented toward less distinctive recollections (colored font). However, the corresponding neural activity de-pended on the type of monitoring engaged on these tests. Rejecting items based on the absence of picture recollections (i.e., the distinctiveness heuristic) decreased activity in dorsolat-eral prefrontal cortex relative to the control test, whereas rejecting items based on successful picture recollections (i.e., a recall-to-reject strategy) increased activity in dorsolateral prefrontal cortex. There also was some evidence that these effects were differentially lateralized. This study provides the first neuroimaging compari-son of these two recollection-based monitoring processes and ad-vances theories of prefrontal involvement in memory retrieval.