When you learn something new, the best way to retain that information is to sleep. Sleep helps consolidate the memories formed throughout the day and links new memories with previous ones.
The relationship between memory and sleep has been studied by scientists worldwide since the early 19th century.
Long-term memory formation is one of the main functions of sleep. (Photo: iStock)
To date, hundreds of studies have consistently shown that sleep plays a crucial role in the memory consolidation process— a process in which the brain categorizes daily experiences and selects specific events to store in long-term memory.
Dr. Matthew Walker, a sleep scientist at the University of California, Berkeley, states that sleep and memory share a complex relationship. Adequate rest helps keep the mind sharp, thereby assisting in the quick processing of encountered information. Moreover, sleeping after learning helps reinforce information into memory, allowing for storage in the brain.
A healthy adult’s sleep consists of four stages:
- Stages 1 and 2 are referred to as light NREM sleep,
- Stage 3 is deep NREM sleep.
- Stage 4 is REM sleep—the stage with rapid eye movement and dreams.
Among these, the three NREM stages help the brain recover after a long day and prepare to learn new information the following day. Insufficient sleep or sleep deprivation can reduce your ability to learn new things by up to 40%.
Dr. Walker emphasizes that you cannot pull an all-nighter and still study effectively. Sleep deprivation affects a part of the brain called the hippocampus, which is vital for forming new memories.
Sleep and memory share a complex relationship. (Photo: iStock).
You accumulate many memories from every moment while awake, but most will be forgotten throughout the day. “When memories begin to form, they are very crude and fragile,” says Dr. Robert Stickgold, a sleep expert at Harvard Medical School.
However, when you drift off to sleep, during NREM sleep, the brain starts organizing recent memories, filtering important ones and discarding other information.
Selected memories are transferred into NREM sleep and become more refined, a process that continues during REM sleep. “During a night of sleep, some memories are consolidated,” Dr. Stickgold explains.
In REM sleep, your newly formed memories are connected with previous memories, including life experiences as well as your library of events and knowledge.
Dr. Andrew E. Budson from Harvard Medical School states that the link between recent memories and prior knowledge is one reason you may wake up with a fresh and valuable perspective on a problem, even a complete solution.
This phenomenon occurred with Dmitri Mendeleev, who struggled for months to organize the atomic elements in the periodic table. In a dream on February 17, 1869, he glimpsed the positions of all the elements, and after jotting down what he dreamed, he only needed to correct one minor error.
Additionally, REM sleep also aids in processing emotions. When you experience negative emotions, you often feel better upon waking the next day, and you will cope with difficult situations or experiences more easily.
REM sleep also helps process emotions. (Source: iStock).
However, the quality of sleep changes as we age. A study by Dr. Matthew Walker and colleagues found that individuals over 60 experience a 70% reduction in deep sleep compared to younger people aged 18-25.
This relates to slow-wave sleep. Slow waves are generated in a brain region called the medial prefrontal cortex. The medial prefrontal cortex weakens over time, leading older adults to experience less slow-wave sleep during a normal sleep cycle and have more difficulty processing memories.
Given that memory decline is associated with reduced deep sleep, scientists are currently researching methods to enhance deep sleep stages to improve memory in this older population.
For younger individuals, especially students, Dr. Stickgold emphasizes that staying up late to study is not as effective as getting enough sleep before and after studying to enhance new memory retention and reinforce learned knowledge.