Medial prefrontal cortex plays a critical and selective role in 'feeling of knowing' meta-memory judgments

The frontal lobes are thought to play a role in the monitoring of memory performance, or 'meta-memory', but the specific circuits involved have yet to be definitively established. Medial prefrontal cortex in general and the anterior cingulate cortex in particular, have been implicated in other forms of monitoring, such as error and conflict monitoring. Here, we tested the hypothesis that medial prefrontal cortex plays a critical role in memory monitoring, aiming to determine whether this region contributed to all, or only some classes of meta-memory judgments. We also investigated the relationship between these judgments and memory performance itself. Three types of meta-memory judgment were measured in 5 subjects with focal damage to medial prefrontal cortex, with maximal overlap in dorsal anterior cingulate cortex, compared to 19 healthy, demographically matched control subjects performing a face-name episodic memory task. Judgment-of-learning accuracy was not affected by such damage. In contrast, both recall confidence and feeling-of-knowing judgments were impaired. Memory performance was itself impaired in the patient group, so we performed a second experiment to examine the relationship between memory and meta-memory deficits. In an easier memory task, where patients performed as well as controls, recall confidence accuracy improved to within the control range despite medial prefrontal damage. In contrast, feeling-of-knowing judgments remained less accurate in the patient group. These results argue that medial prefrontal cortex plays a critical role in generating accurate recall confidence and feeling-of-knowing judgments, but is not necessary for judgment-of-learning. The role of this region in feeling-of-knowing seems to be, at least in part, independent of its role in memory itself.