May 2011

A central hypothesis in the field of memory research is that memories can exist in an active state where they are labile and susceptible to disturbing influences, and in an inactive or stable state during which they are resistant to amnestic treatment. However, the relatively new concept of ‘‘reconsolidation’’ assumes that newly acquired memories are not consolidated once and forever. Rather, reactivation of new memories during wakefulness places the memories into a destabilized state, and reconsolidation is required to transform labile memories into stable memories. Reactivations of memories are also known to take place during sleep, especially slow-wave sleep (SWS), and it has been assumed that this contributes to the consolidating effect of sleep. In this study, Diekelmann and colleagues tested whether the same principle of transient destabilization during wakefulness applies to memory reactivation during SWS. Memories in humans were reactivated by presenting associated odor cues either during SWS or wakefulness. Reactivation was then followed by an interference task to probe memory stability. As expected, reactivation during waking destabilized memories. In contrast, reactivation during SWS immediately stabilized memories, thereby directly increasing their resistance to interference. Functional magnetic resonance imaging revealed that reactivation during SWS mainly activated hippocampal and posterior cortical regions, whereas reactivation during wakefulness primarily activated prefrontal cortical areas. These results show that reactivation of memory serves distinct functions depending on the brain state of wakefulness or sleep. Such differences may be important in the design of approaches for treating maladaptive memories, such as those that exist in panic disorder and post-traumatic stress disorder (Nat. Neurosci. 2011, 14:381–388).