Strengthening memories during sleep

Reactivating newly learned memories during sleep can strengthen the memory trace, reports a study published online this week in Nature Neuroscience. These findings could have clinical implications for treating disorders such as post-traumatic stress syndromes.

Previous studies have shown that reactivating newly formed memories during a wakeful period soon after learning can actually destabilize the memory trace, making such memories less robust.

Bjorn Rasch and colleagues trained subjects in a spatial memory task, where they had to learn an object location in a grid, while an odor was concurrently presented. After participants formed a memory of this odor-object association, one group of subjects slept while another group stayed awake for a comparable time period. During this period of wakefulness or slow-wave sleep, the odor from the learning task was presented again to the subjects, which presumably triggered a reactivation of the memory. The authors found that reactivation during sleep improved memory retention later on, whereas reactivation when awake impaired it.? The scientists also performed functional magnetic resonance imaging (fMRI) to show that memory reactivation via odor presentation during wakeful periods involved different patterns of brain activity than that seen during sleep.

This finding suggests that memory reactivation can have opposing effects on memory presentation depending on whether the reactivation was done during sleep or when awake.