These two brain wave patterns represent how the brain processes memories as people sleep – and it is all about timing. Short for electroencephalogram, an EEG detects brain waves like the bursts of electrical activity known as sleep spindles and slower sleep waves called slow oscillations. Neuroscientists can eavesdrop on the brain at work, day or night, using a technique called EEG. Then the reactivated memories pass through the thalamus, a central crossroads in the brain, so they can be embedded in the neocortex for long-term storage. First, the hippocampus, the part of the brain that stores memories temporarily, replays the memories of the day. As we lie asleep, unconscious, our brain is busy processing the day’s memories, which travel through three parts of the brain before they are filed away. Sleep is essential for consolidating the memories that we made during the day. Our results provide evidence that improved coordination between SOs and spindles indexes the development of sleep-dependent memory networks. Critically, this increase indicated enhanced memory formation from childhood to adolescence. Consequently, we devised an individualized cross-frequency coupling approach, which demonstrates that SO-spindle coupling strength increases during maturation. After disentangling oscillatory components from 1/f activity, we found frequency shifts within SO and spindle frequency bands. Performance on the memory task was better during adolescence. Here, we use a longitudinal study design spanning from childhood to adolescence, where participants underwent polysomnography and performed a declarative word-pair learning task.
Critically, it remains unknown how the precise temporal coordination of these two sleep oscillations develops during brain maturation and whether their synchronization indexes the development of memory networks. SO and spindle morphology changes considerably throughout development. Precise temporal coordination of slow oscillations (SO) and sleep spindles is a fundamental mechanism of sleep-dependent memory consolidation.