Right dorsolateral prefrontal cortex is engaged during post-retrieval processing of both episodic and semantic information

Abstract

Post-retrieval processes are engaged when the outcome of a retrieval attempt must be monitored or evaluated. Functional neuroimaging studies have implicated right dorsolateral prefrontal cortex (DLPFC) as playing a role in post-retrieval processing. The present study used fMRI to investigate whether retrieval-related neural activity in DLPFC is associated specifically with monitoring the episodic content of a retrieval attempt. During study, subjects were cued to make one of two semantic judgments on serially presented pictures. One study phase was followed by a source memory task, in which subjects responded 'new' to unstudied pictures, and signaled the semantic judgment made on each studied picture. A separate study phase was followed by a task in which the studied items were subjected to a judgment about their semantic attributes. Both tasks required that retrieved information be evaluated prior to response selection, but only the source memory task required evaluation of retrieved episodic information. In both tasks, activity in a common region of right DLPFC was greater for studied than for unstudied items, and the magnitude of this effect did not differ between the tasks. Together with the results of a parallel event-related potential study [Hayama, H. R., Johnson, J. D., & Rugg, M. D. (2008). The relationship between the right frontal old/new ERP effect and post-retrieval monitoring: Specific or non-specific? Neuropsychologia, 46(5), 1211-1223, doi:S0028-3932(07)00390-9], the present findings indicate that putative right DLPFC correlates of post-retrieval processing are not associated exclusively with monitoring or evaluating episodic content. Rather, the effects likely reflect processing associated with monitoring or decision-making in multiple cognitive domains.

Figure 1

A: Regions identified with the early HRF where retrieval success (old>new) effects (p<.001) were common to the two tasks, overlaid on a rendered canonical brain. These regions included (i) Left anterior prefrontal cortex, (ii) Left inferior/middle frontal gyrus, and (iii) left superior parietal cortex. Graphs depict mean parameter estimates (arbitrary units) and standard errors of activity in the peak voxels (MNI coordinates) for each cluster. **p < 0.005; *** p < 0.001 B: Retrieval success effects common to the two task (Green), displayed with success effects from the source task alone (Red). Overlapping regions are shown in yellow. Data are displayed on a sagittal section a (x = −46) of a canonical MNI template brain (all effects thresholded at p<.001).

Figure 2

Regions identified with the late HRF where retrieval success effects were common to the two tasks, overlaid on a rendered canonical brain. Bar graph shows the peak parameter estimates (arbitrary units) and standard errors for the peak voxel of the right DLPFC cluster; ** p < 0.005; *** p < 0.001. Also illustrated are the time courses of the BOLD responses averaged within a 5mm radius sphere centered on the peak voxel of the right DLPFC cluster for each class of test items. The x- and y- axis units are in seconds and percent signal change, respectively.

Figure 3

Regions identified with the early HRF where activity was greater for correct rejections than for hits (new>old effects) regardless of task. Effects are displayed on coronal and sagittal sections of the across-subject mean of the normalized T₁-weighted images. Graphs depict mean parameter estimates (arbitrary units) and standard errors of activity in the indicated peak voxels (MNI coordinates). *p < 0.05; **p < 0.005; ***p < 0.001.