The role of the right anterior prefrontal cortex in episodic retrieval

Regional brain activity was measured with H-2 O-15 PET while participants a ttempted to complete word-stem and word-fragment retrieval cues with previo usly studied words. The retrieval cue manipulation was employed to gain con trol over the monitoring operations associated with evaluating the episodic status of alternative cue completions, These operations were more constrai ned for fragments, which had fewer possible completions than each correspon ding stem. In one condition (zero target), during the scanning interval non e of the cues could be completed with studied items, whereas in another con dition (high target), 80% of cues belonged to studied items. Relative to ba seline tasks, right anterior prefrontal activity was greater for stems than for fragments in the zero target condition. The target density manipulatio n did not modulate right anterior prefrontal activity, but was associated w ith increased activity in right dorsolateral prefrontal cortex. These findi ngs are consistent with the proposal that the right anterior prefrontal cor tex supports monitoring operations during episodic retrieval tasks. In addi tion, the findings add to evidence suggesting that the dorsolateral and ant erior right prefrontal cortex make functionally distinct contributions to e pisodic retrieval. (C) 2000 Academic Press.