Research highlights

Order Matters: New Insights into Sleep Cycles

A new study conducted by members of the CRCN, Mélanie Strauss and Philippe Peigneux shows: the order of our different sleep phases matters!


Sleep consists of two main stages that always appear in the same order. First, slow-wave or non-rapid-eye-movement (NREM) sleep, followed by paradoxical or REM sleep. We already know that sleep plays an important role in memory consolidation. What was so far unknown is whether the order of the two sleep stages is important for this consolidation to happen. This new study demonstrates that the order is indeed important. Mélanie Strauss and her colleagues studied a group of people with narcolepsy. This is a rare sleep disorder which leads people to frequently fall asleep straight into paradoxical or REM sleep, without passing first through a phase of slow-wave sleep.

The researchers compared the memory consolidation after naps featuring the normal NREM-REM (N-R) sequence with naps featuring the reversed sequences (REM-NREM, R-N). They found that indeed, memory consolidation is hindered if the typical sleep pattern is reversed. So-called sleep spindles, an electrophysiological marker of learning, is only related to memory consolidation in the physiological NREM-REM sequence, with the typical order of sleep phases. This is study is one of the first experimentally demonstrating the sequential role of sleep stages for memory consolidation in humans. Further, the rapid eye movements during paradoxical sleep  were associated with less memory consolidation. These findings further reinforce the complex role in the fragile balance between remembering and forgetting.

Order Matters: New Insights into Sleep Cycles


This article was published in the Journal Sleep:

Mélanie Strauss, Lucie Griffon, Pascal Van Beers, Maxime Elbaz, Jason Bouziotis, Fabien Sauvet, Mounir Chenaoui, Damien Léger, Philippe Peigneux, Order matters: sleep spindles contribute to memory consolidation only when followed by rapid-eye-movement sleep, Sleep, 2022;, zsac022,