Semantic retrieval, mnemonic control, and prefrontal cortex.

Accessing stored knowledge is a fundamental function of the cognitive and neural architectures of memory. Here, the authors review evidence from cognitive-behavioral paradigms, neuropsychological studies of patients with focal neural insult, and functional brain imaging concerning the mechanisms underlying retrieval of semantic knowledge and their association with prefrontal cortex. First, the authors examine behavioral and neuropsychological evidence distinguishing between controlled and automatic semantic retrieval. Then the authors review the subregions of prefrontal cortex that functional neuroimaging has associated with semantic retrieval across a range of memory demanding tasks. Finally, two hypotheses concerning the nature of processing in these brain regions--the controlled semantic retrieval and selection hypotheses--are critically examined, and a possible synthesis is proposed.