Rostral prefrontal cortex and the focus of attention in prospective memory

Abstract

Prospective memory (PM) denotes the function to realize intentions after a delay while being immersed in distracting ongoing (OG) activity. Here, we scrutinize the often-reported involvement of rostral prefrontal cortex (rPFC; approximating Brodmann area 10) in such situations: This region might mediate attention between external stimuli and the internally maintained intention, that is, between stimulus-oriented (SO) and stimulus-independent (SI) processing. Using functional magnetic resonance imaging (fMRI) we orthogonally crossed 1) PM versus OG activity only, with 2) SO versus SI attention. In support of the hypothesis, common regions of medial rPFC exhibited greater blood oxygen level-dependent (BOLD) signal for the contrasts of both OG task only versus PM and SO versus SI attending. However, activation related to the former contrast extended more superiorly, suggesting a functional gradient along a dorsal-ventral axis within this region. Moreover, region-of-interest analyses revealed that PM versus OG task only was associated with greater BOLD signal in left lateral rPFC, reflecting the requirement to maintain delayed intentions. Distinct aspects of this region were also transiently engaged at transitions between SO and SI conditions. These results are consistent with the hypothesis that some of the rostral prefrontal signal changes associated with PM performance reflect relative differences in SO versus SI processing.

Figure 1.

Illustration of the block structure. SO, stimulus-oriented; SI, stimulus-independent; PM, prospective memory.

Figure 2.

Behavioral results as a function of task, PM condition (OG, ongoing task only; PM, prospective memory), stimulus phase (SO, stimulus-oriented; SI, stimulus-independent), and trial type. Error bars indicate standard error of means.

Figure 3.

(a,b) BOLD signal changes within rPFC (thresholded at P < 0.05, FWE corrected for BA 10). (c) Parameter estimates from the peak of overlap between a and b. Error bars indicate standard error of means. OG, ongoing only; PM, prospective memory; SO, stimulus-oriented; SI, stimulus-independent.

Figure 4.

(a) BOLD signal changes for the contrasts 1) ongoing only versus prospective memory (OG > PM) and 2) stimulus-oriented versus stimulus-independent (SO > SI), and 3) for the overlap between both contrasts (thresholded at P < 0.001, uncorrected; averaged across both tasks). (b) Mean z-coordinates of the peak voxels for the individual contrast within each sagittal plane of rostromedial prefrontal cortex. Error bars indicate standard error of means.

Figure 5.

Parameter estimates from the ROI analyses within (a) left and (b) right rostrolateral prefrontal cortex. Error bars indicate standard error of means. OG, ongoing only; PM, prospective memory; SO, stimulus-oriented; SI, stimulus-independent.

Figure 6.

BOLD signal changes for the contrast switch versus stay and associated regressor estimates for (a) left lateral, (b) medial, and (c) right lateral rPFC (thresholded at P < 0.05, FWE corrected for BA 10). OG, ongoing only; PM, prospective memory; SO, stimulus-oriented; SI, stimulus-independent; Sw: switch; St: stay.