Direct comparison of prefrontal cortex regions engaged by working and long-term memory tasks. 
Neuroimaging studies have suggested the involvement of ventrolateral, dorsolateral, and frontopolar prefrontal cortex (PFC) regions in both working (WM) and long-term memory (LTM).  The current study used functional magnetic resonance imaging (fMRI) to directly compare whether these PFC regions show selective activation associated with one memory domain.  In a within-subjects design, subjects performed the n-back WM task (two-back condition) as well as LTM encoding (intentional memorization) and retrieval (yes-no recognition) tasks.  Additionally, each task was performed with two different types of stimulus materials (familiar words, unfamiliar faces) in order to determine the influence of material-type vs task-type.  A bilateral region of dorsolateral PFC (DL-PFC; BA 46/9) was found to be selectively activated during the two-back condition, consistent with a hypothesized role for this region in active maintenance and/or manipulation of information in WM.  Left frontopolar PFC (FP-PFC) was also found to be selectively engaged during the two-back.  Although FP-PFC activity has been previously associated with retrieval from LTM, no frontopolar regions were found to be selectively engaged by retrieval.  Finally, lateralized ventrolateral PFC (VL-PFC) regions were found to be selectively engaged by material-type, but uninfluenced by task-type.  These results highlight the importance of examining PFC activity across multiple memory domains, both for functionally differentiating PFC regions (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).