Past research has shown that judgments of learning (JOLs), subjective confidence judgments made at study about later memorability, are inferential in nature and based on cues available during encoding. Participants tend to use fluency as a cue and give higher JOLs to more fluently encoded items, despite having better recognition memory for disfluently encoded items, which leads to poor JOL accuracy. Research has implicated the dorsolateral prefrontal cortex (DLPFC) and anterior prefrontal cortex (aPFC) in JOL and encoding processes, but no studies to date have tested how the roles of these regions vary with the information on which JOLs are based. We used high-definition transcranial direct current stimulation to test the causal roles of DLPFC and aPFC in encoding success, JOL ratings, and JOL accuracy. Participants studied and made JOLs about words that varied in fluency (i.e., frequency and orientation). High-definition transcranial direct current stimulation over the DLPFC impaired encoding, as evidenced by an increase in subsequent false alarms. For words that were less fluently encoded, aPFC stimulation improved JOL accuracy, perhaps making participants more aware of encoding failures under conditions of disfluency. Conversely, DLPFC and aPFC stimulation decreased JOL accuracy for high-frequency words, suggesting the roles of these regions in JOLs vary with the cognitive bases of the judgments. These results contribute to our understanding of the causal roles of prefrontal regions in objective and subjective memory processes and how their contributions to metamemory accuracy vary with information on which subjective assessments are based.

Metamemory refers to knowledge and monitoring of one's own memory. Metamemory monitoring can be done prospectively with respect to subsequent memory retrieval or retrospectively with respect to previous memory retrieval. In this study, we used fMRI to compare neural activity during prospective feeling-of-knowing and retrospective confidence tasks in order to examine common and distinct mechanisms supporting multiple forms of metamemory monitoring. Both metamemory tasks, compared to non-metamemory tasks, were associated with greater activity in medial prefrontal, medial parietal, and lateral parietal regions, which have previously been implicated in internally directed cognition. Furthermore, compared to non-metamemory tasks, metamemory tasks were associated with less activity in occipital regions, and in lateral inferior frontal and dorsal medial prefrontal regions, which have previously shown involvement in visual processing and stimulus-oriented attention, respectively. Thus, neural activity related to metamemory is characterized by both a shift toward internally directed cognition and away from externally directed cognition. Several regions demonstrated differences in neural activity between feeling-of-knowing and confidence tasks, including fusiform, medial temporal lobe, and medial parietal regions; furthermore, these regions also showed interaction effects between task and the subjective metamemory rating, suggesting that they are sensitive to the information monitored in each particular task. These findings demonstrate both common and distinct neural mechanisms supporting metamemory processes and also serve to elucidate the functional roles of previously characterized brain networks.

Successful memory typically implies both objective accuracy and subjective confidence, but there are instances when confidence and accuracy diverge. This dissociation suggests that there may be distinct neural patterns of activation related to confidence and accuracy. We used event-related functional magnetic resonance imaging to study the encoding of novel face–name associations, assessed with a postscan memory test that included objective measures of accuracy and subjective measures of confidence. We showed specific neural activity in the left inferior prefrontal cortex associated with trials when subjects expressed high confidence that they had chosen the correct name for the face and made a correct identification. Moreover, we found that this region was also associated with imparting high confidence when subjects chose the incorrect name. However, medial temporal lobe regions showed activity only for high-confidence correct trials. Many functional magnetic resonance imaging studies have shown that the medial temporal lobe and left prefrontal regions are particularly important for the successful formation of memories by using a combination of subjective and objective measures. Our findings suggest that these regions may be differentially involved in the objective and subjective components of memory and that the origins of confidence–accuracy dissociations may be related to incomplete activation of the neural pattern seen in successful encoding. These findings may also aid understanding of eyewitness misidentifications and memory distortions.