Sleep reorganizes declarative memories from hippocampal towards cortical storing sites

Declarative memory consolidation is supposed to rely on a time-dependent process that gradually incorporates recently acquired hippocampal memory traces into cortical long-term knowledge structures. Besides the mere passage of time sleep appears to provide central nervous conditions that facilitate declarative memory consolidation. However, whether sleep also contributes to the reorganization of declarative memories within hippocampal-neocortical networks is unknown. Here we show that sleep makes memories less dependent on the hippocampus while the anterior cingulate and superior temporal cortex become significantly more engaged. Moreover, we found a negative correlation between retrieval-related brain activity in the hippocampus and both of these cortical regions selectively after sleep. Whereas these differential patterns of neuronal activity were related to comparable levels of memory performance additional experiments revealed that only sleep protects the initially vulnerable memory traces against behavioral interference. Our results indicate that sleep consolidates declarative memories by reorganizing them from temporary hippocampal towards cortical long-term storing sites.