Distinct roles for lateral and medial anterior prefrontal cortex in contextual recollection

Abstract

A key feature of human recollection is the ability to remember details of the context in which events were experienced, as well as details of the events themselves. Previous studies have implicated a number of regions of prefrontal cortex in contextual recollection, but the role of anterior prefrontal cortex has so far resisted detailed characterization. We used event-related functional MRI (fMRI) to contrast recollection of two forms of contextual information: 1) decisions one had previously made about stimuli (task memory) and 2) which of two temporally distinct lists those stimuli had been presented in (list memory). In addition, a retrieval cue manipulation permitted evaluation of the stage of the retrieval process in which the activated regions might be involved. The results indicated that anterior prefrontal cortex responded significantly more during recollection of task than list context details. Furthermore, activation profiles for lateral and medial aspects of anterior prefrontal cortex suggested differing roles in recollection. Lateral regions seem to be more involved in the early retrieval specification stages of recollection, with medial regions contributing to later stages (e.g., monitoring and verification).

FIG. 1

Examples of the cues and stimuli used during study and test phases. In the study phase, two temporally distinct lists of items were presented. In each list, participants were pseudo-randomly cued to make entertainment/politics or pleasant/unpleasant judgments about either words or faces. In the test phase, participants were cued to make context memory or baseline decisions about stimuli. In context memory conditions, decisions required recollection of whether stimuli had been studied in list 1 or list 2 or whether the entertainment/politics or pleasant/unpleasant task had been undertaken. In baseline conditions, participants responded by pressing the 1 key or 2 key in the cue-only conditions (1st 2 panels) or made living/nonliving or male/female decisions in the semantic baseline conditions (final 2 panels).

FIG. 2

Group functional activation maps, displayed on axial slices of an averaged structural image, of the study phase contrast between pleasantness and semantic judgments. Significant activation can be seen in medial anterior prefrontal cortex (PFC), in a very similar region to that observed by Gusnard et al. (2001), as well as in other PFC regions.

FIG. 3

Regions associated with contextual recollection in the test phase. Significant activation during recollection of (A) task and (B) list seen in similar regions of bilateral anterior PFC, ventrolateral PFC/insula, dorsolateral PFC, lateral parietal cortex, and precuneus. C: contrasting task and list recollection directly revealed significant activation in lateral and medial regions of left anterior PFC, left ventrolateral PFC, and precuneus.

FIG. 4

Regions common to both context recollection and cue-only conditions included left lateral anterior and ventrolateral PFC and bilateral posterior fusiform cortex. These regions may play a role in retrieval orientation processes.

FIG. 5

Time-course analysis suggesting that lateral (in black) and medial (in gray) anterior PFC are involved in temporally distinct stages of the recollection process. Error bars denote SE.