The formation of new memories is only possible during certain phases of sleep, shows a study published this week in Nature Communications. Rapid eye-movement (REM) or light, non-REM (NREM) sleep is found to be conducive to learning, whereas deep NREM sleep had a suppressive effect on the ability to learn new information. The findings may help us to understand more about the function of distinctive phases of sleep.
Previous research investigating whether or not we can learn during sleep has produced mixed results, with some studies showing that people can learn while asleep, and others failing to provide evidence of new memory formation during sleep. Thomas Andrillon and colleagues propose that these discrepancies may be due to the fact that different sleep stages are characterized by different types of brain activity, which could potentially explain why people sometimes could learn and sometimes could not. To test this hypothesis, the authors measured brain activity in sleeping participants and played them various sequences of sound. When the participants woke, they were tested on how well they were able to recognize the sounds they heard while they were asleep. Hearing the sequences during REM improved peoples’ performance on this task, whereas hearing the sequences during NREM sleep decreased performance. By analysing peoples’ responses to sounds during the night, the authors could confirm the learning effect in REM sleep. In NREM sleep, they observed a sharp distinction between light NREM sleep, during which learning was possible, and deep NREM sleep, during which learning was suppressed.
Taken together, these results not only show that you can learn during sleep but shed light on general memory processes and how they change during different sleep stages.