Functional network in the prefrontal cortex during episodic memory retrieval.

A recent consistent finding in neuroimaging studies of human memory is that the prefrontal cortex (PFC) is activated during episodic memory retrieval. To date, however, there has been no direct evidence to explain how activity in the right and left PFC and in the anterior and posterior PFC are functionally interconnected. The goal of the present study was to obtain such evidence by event-related functional magnetic resonance imaging (MRI) and the functional connectivity method. Subjects were first asked to try to remember a series of associate-word lists outside the MRI scanner in preparation for a later recognition test. In the MRI scanning phase, they were asked to make recognition judgments in regard to old words, semantically related lure words, and unrelated new words. The analysis of functional connectivity revealed that the posterior PFC in each hemisphere had strong functional interconnections with the contralateral posterior PFC, whereas the anterior PFC in each hemisphere had only weak functional interconnections with the contralateral anterior PFC. No strong functional interconnections were found between the anterior and posterior PFC in either hemisphere. These findings support the hypothesis of an associative contribution of the bilateral posterior PFC to episodic memory retrieval and a dissociative contribution of the bilateral anterior PFC.