Parietal Activity in Labile and Stabilized Memory of Boolean Rules

Using event-related functional magnetic resonance imaging (fMRI) and the Ebbinghaus paradigm, we investigated the effect of memory in parietal cortex activity. In the course of one week, participants learned Boolean arithmetic tasks and were asked to master them perfectly. We measured cerebral activation with fMRI while healthy volunteers had learned and practiced Boolean rules on day 1 (i.e., labile memory condition) and day 7 (i.e., stabilized condition). A network of cortical areas was found to be differently activated during retrieval of labile and stabilized memory, including the left superior parietal lobule and precuneus for labile memory and the left inferior parietal lobule and postcentral gyrus for labile and stabilized memory. These results show that state-specific cortical networks are systematically activated during memory retrieval. We propose that memory stability following the automatic retrieval of rules involves information clustering across time and, simultaneously, to process the repetitive Boolean problems with minimal resources by mediation of parietal areas.