Abstract
Using fMRI, we investigated whether the oft-reported rostral prefrontal cortex (PFC) activations during prospec- tive memory paradigms (i.e., realization of delayed intentions that are not directly cued by the environment) might reflect the demands that such tasks make for selection between stimulus-oriented (i.e., environ- mentally prompted) and stimulus-independent (i.e., environmentally decoupled) attending. Using a 2x2 factorial design, we crossed (i) pro- spective memory vs. ongoing task only, with (ii) stimulus-oriented vs. stimulus-independent attending, across two tasks that differed in stimu- lus form and background processing requirements. In support of the hypothesis, common regions of activation within rostromedial PFC were revealed by comparing the ongoing task only with the prospective mem- ory condition, and the stimulus-oriented with the stimulus-independent condition. However, activation related to the former contrast extended more superiorly, suggesting a functional gradient along a dorsal-ventral axis within this region. Moreover, the prospective memory compared with the ongoing task only condition recruited left rostrolateral PFC, reflecting the requirement to maintain delayed intentions. Distinct aspects of this region were also transiently activated at transitions between stimulus-oriented and stimulus-independent conditions. These results suggest that some of the rostral prefrontal signal changes previ- ously noted during prospective memory tasks may reflect alterations in demands made upon an attentional system that mediates competition between stimulus-oriented and stimulus-independent processing. How- ever, this is unlikely to provide a complete explanation.
