There’s already a strong link between sleep and memory, and scientists have just found out more about how that relationship works: there are specific patterns of brain activity that open up windows on our past experiences, fixing them in our long-term memory.

These patterns involve the slow oscillations (SOs) of brain waves that normally accompany sleep, and the sharper sleep spindle bursts of activity that happen during dreamless slumber. It now seems that the precise way these two types of brain activity coordinate with each other makes a big difference in how well we remember something.

Our memories are essentially being reactivated during sleep via these two brain activity patterns, the researchers suggest, making us more likely to remember them. The stronger the reactivation, the more likely we are to be able to recall a memory later on.