Direct comparison of prefrontal cortex regions engaged by working and long-term memory tasks

Neuroimaging studies have suggested the involvement of ventrolateral, dorso lateral, and frontopolar prefrontal cortex (PFC) regions in both working (W M) and long-term memory (LTM). The current study used functional magnetic r esonance imaging (fMRI) to directly compare whether these PFC regions show selective activation associated with one memory domain. Ina within-subjects design, subjects performed the n-back WM task (two-back condition) as well as LTM encoding: (intentional memorization) and retrieval (yes-no recognit ion) tasks. Additionally, each task was performed with two different types of stimulus materials (familiar words, unfamiliar faces) in order to determ ine the influence of material-type vs task-type. A bilateral region of dors olateral PFC (DL-PFC; BA 46/9) was found to be selectively activated during the two-back condition, consistent with a hypothesized role for this regio n in active maintenance and/or manipulation of information in WM. Left fron topolar PFC (FP-PFC) was also found to be selectively engaged during the tw o-back. Although FP-PFC activity has been previously associated with retrie val from LTM, no frontopolar regions were found to be selectively engaged b y retrieval. Finally, lateralized ventrolateral PFC (VL-PFC) regions were f ound to be selectively engaged by material-type, but uninfluenced by task-t ype. These results highlight the importance of examining PFC activity acros s multiple memory domains, both for functionally differentiating PFC region s (e.g., task-selectivity vs material-selectivity in DL-PFC and VL-PFC) and for testing the applicability of memory domain-specific theories (e.g., FP -PFC in LTM retrieval). (C) 2001 Academic Press.