Functional dissociations in prefrontal–hippocampal working memory systems

The frontal lobe and hippocampal regions are critically involved in memory processing, yet there are limited data providing the timing information that identifies the nature and specific roles of these regions in memory tasks. The present study investigated event-related neural activity using magnetoencephalography (MEG) with a visual working memory (WM) paradigm. Results showed prefrontal and hippocampal activations dissociated in timing, and with different levels of memory processing. We identified sustained frontal polar activation sensitive to correct recognition of repeated stimuli, differentiated from rapid responses of the dorsal lateral prefrontal cortex to the encoding of novel stimuli, during tasks of higher memory demand. We also found early, left hippocampal activation during immediate encoding, versus later, right hippocampal activation during immediate recognition, in tasks of lower memory load. The present MEG data provide valuable timing information on processes in WM, offering new insights into functional specializations of the prefrontal – hippocampal WM systems.