The role of VMPC in metamemorial judgments of content retrievability

Abstract

Making judgments about the retrievability of information is a critical part of the metamemory processes engaged during remembering. A recent study of patients with frontal lesions suggests that ventral medial prefrontal cortex (VMPC) plays a critical role in such judgments [Schnyer, D. M., Verfaellie, M., Alexander, M. P., Lafleche, G., Nicholls, L., & Kaszniak, A. W. A role for right medial prefrontal cortex in accurate feeling of knowing judgments: Evidence from patients with lesions to frontal cortex. Neuropsychologia, 42, 957-966, 2004]. The observed impairment was thought to reflect an inability to determine the accessibility of memory contents. To further examine the neuroanatomical basis of content accessibility assessment, we used fMRI in an episodic feeling-of-knowing (FOK) paradigm. Participants were asked to make trial-by-trial predictions about the retrievability of the final word that completed studied sentences and then to select the correct completion from among alternatives. Results indicated that the VMPC is engaged during accurate FOK judgments and its activation is modulated by retrieval rating. Structural equations modeling supported the notion that VMPC, as part of a broader left hemisphere network involved in memory retrieval, monitors the output of the retrieval process. More generally, VMPC may participate in metacognitive processes that allow for the comparison of available data against an internal model.

Figure 1

Schematic of the three screens that make up a single trial in the FOK judgment task. Both the judgment and recognition decision screens are presented until a choice is made or for a maximum of 10 sec. The fixation screen appears for a randomly determined duration of either 6, 8, or 10 sec. The three periods are separated by a 500-msec interstimulus interval.

Figure 2

Panels show eleven 5-mm axially oriented slices of a normalized T1 structural image with overlays of significant voxels identified by the indicated contrast. All voxels shown survived the cluster correction for multiple comparisons at p < .05. (A) Accurate “know” judgments greater than all inaccurate judgments; (B) Accurate 1–4 judgments greater than all inaccurate judgments; (C) The significant conjunction between panels A and B.

Figure 3

Four critical left hemisphere regions revealed by the contrast of accurate judgments > inaccurate judgments. The images and MNI coordinates indicate the local maximum. Below each region is a time-course graph of extracted signal levels used for SEM. The three conditions (accurate judgments, inaccurate judgments, and “know” trials) are indicated with separate colored lines and reflect data averaged across the identified cluster. The y-axis of this graph is normalized percent signal change and the x-axis is poststimulus time from 0 to 16 sec. All time courses are baselined to the average of −4 to 0 sec prestimulus onset. LIPC = left inferior prefrontal cortex; LHip = left hippocampus; LTemp = left temporal cortex; VMPC = ventral medial prefrontal cortex.

Figure 4

Results of SEM for regions involved in judgment accuracy. (A) The initial model utilized for SEM selection. (B) The model solution and pathways for the accurate 1–4 judgments. (C) The model solution and path coefficients for the sentence control task. Below the model schematic on the left are the fit parameters for the two emergent models and the results of path coefficients comparisons. A statistically significant chi-squared difference (χ²_Diff) indicates that path coefficients are different between models B and C. On the right is the correlation matrix for the four regions used in model fitting for accurate 1–4 judgments.

Figure 5

Region of the VMPC that modulates linearly with 1–4 ratings. The graph represents the model amplitude fitted in SPM99 for all ratings within the voxel identified by the group maxima (0, 30, −6). Ratings with subscripts in common are not significantly different from each other ( p < .05). The y-axis is percent signal change and error bars represent the standard error of the mean across subjects.