Organization of working memory within the human prefrontal cortex: a PET study of self-ordered object working memory

The prefrontal cortex plays a critical role in working memory, the active maintenance of information for brief periods of time for guiding future motor and cognitive processes. Two competing models have emerged to account for the growing human and non-human primate literature examining the functional neuroanatomy of working memory. One theory holds that the lateral frontal cortex plays a domain-specific role in working memory with the dorsolateral and ventrolateral cortical regions supporting working memory for spatial and non-spatial material, respectively. Alternatively, the lateral frontal cortex may play a process-specific role with the more dorsal regions becoming recruited whenever active manipulation or monitoring of information in working memory becomes necessary. Many working memory tasks do not allow for direct tests of these competing models. The present study used a novel self-ordered working memory task and positron emission tomography to identify whether dorsal or ventral lateral cortical areas are recruited during a working memory task that required extensive monitoring of non-spatial information held within working memory. We observed increased blood flow in the right dorsolateral, but not ventrolateral, prefrontal cortex. Increases in blood flow in the dorsolateral region correlated strongly with task performance. Thus, the results support the process-specific hypothesis.