A new study shows how people learn while they sleep and how sleep phases promote this. Two different sleep phasesduring deep sleepappear to play an important, complementary role in learning. One improves overall performance, while the other stabilizes what the sleeping person learned the day before.
How can people learn in their sleep?
Scientists have long known that a good night's sleep does wonders for one's ability to learn new skills. What has been less clear, however, is the role of different sleep stages. In particular, there has been controversy over the relative contributions of rapid eye movement (REM) sleep, when most dreams occur, and non-REM sleep, which is largely dreamless. A study by psychologists at Brown University's Institute for Cognitive, Linguistic and Psychological Sciences provides important clues that could help resolve the debate. Their experiment focuses primarily on visual learning. It suggests that it is not one stage that is more important than the other for learning new skills, but rather that neurochemical processing plays both an essential and complementary role.
The team found that while non-REM sleep improves the performance of newly acquired skills by restoring flexibility, REM sleep stabilizes these improvements. This sleep phase also prevents the new information from being overwritten by subsequent learning. Most REM sleep occurs in the final hours of sleep, so the finding reinforces the importance of not shortening these later stages. When people sleep at night, there are many sleep cycles. REM sleep occurs at least three, four, five times, especially in the later part of the night. In addition, people need a lot of REM sleep so that they can better remember what they have learned. Therefore, this sleep should take place uninterrupted.
Benefits of sleep for learning
Psychologists have previously identified two distinct benefits of sleep for learning. They often refer to the first benefit as “offline performance improvement.” This is that the learning acquired before going to sleep improves after sleep without additional training. The second advantage, considered resilience to interference, protects skills learned before sleep from interference or overwriting by subsequent learning after waking. To take advantage of both advantages, there is a trade-off between flexibility and stability. Learning during the day involves the formation of new synapses, which are the electrical connections between nerve cells. Accordingly, strengthening existing synapses depends on repeated use. As people learn in their sleep, the brain appears to streamline its operations to work more efficiently.
One leading hypothesis is that the brain reactivates synapses that grow stronger or weaker at random throughout the day. This restores flexibility or plasticity to the brain's local connections and broader networks to improve overall performance. At the same time, the brain must stabilize important synapses during sleep to prevent new learning experiences from eliminating what was learned the day before.
The researchers used electrodes taped to the subjects' eyelids and scalp. This allowed them to determine when the subjects entered different stages of sleep. They also used a technique called magnetic resonance spectroscopy. This allows the relative concentrations of two neurotransmitters (glutamate and gamma-aminobutyric acid (GABA)) that process visual information to be measured in the parts of the brain. In totalthe results suggest this, that both sleep phases are essential for learning new things. While the brain is “offline,” non-REM sleep improves performance on newly learned tasks. However, without REM sleep to stabilize memories, these gains are lost.
