How does sleep consolidate our memories?

When you learn something new, the best way to remember it is to sleep because sleep helps consolidate the memories you've formed throughout the day and link new memories to previous ones.

The relationship between memory and sleep has been studied by scientists around the world since the early 19th century.

Long-term memory formation is one of the main functions of sleep.

To date, hundreds of studies have shown consistent results that sleep plays a crucial role in memory consolidation — a process by which the brain sorts through the day's experiences and selects certain events to store in long-term memory.

Dr. Matthew Walker, a sleep scientist at the University of California, Berkeley, says sleep and memory share a complex relationship. Getting enough rest helps keep your mind sharp, which helps you process information quickly. And sleeping after studying helps consolidate information into memory, allowing you to store it in your brain.

A healthy adult's sleep will have 4 stages:

Stages 1 and 2 are called light NREM sleep ,

Stage 3 is deep NREM sleep .

Stage 4 is REM sleep – rapid eye movement sleep and dreaming.

The 3 stages of NREM help the brain recover after a long day of work and prepare the brain to learn new information the next day. Insomnia or insufficient sleep can reduce your ability to learn new things by up to 40%.

Dr. Walker says you can’t stay up all night and still study effectively. Lack of sleep affects a part of the brain called the hippocampus, which is important for forming new memories.

Sleep and memory share a complex relationship.

You accumulate memories from every waking moment, but most of them are forgotten during the day. "When memories first form, they're very rudimentary and fragile," says Robert Stickgold, PhD, a sleep specialist at Harvard Medical School.

But when you fall asleep, during NREM sleep, your brain begins to sort through recent memories, filtering out important memories and discarding other information.

Selected memories are consolidated during NREM sleep and become more specific, and this process continues during REM sleep. “During a night’s sleep, some memories are consolidated,” Dr. Stickgold explains.

During REM sleep, your newly consolidated memories are connected to previous memories, including memories of your life as well as your library of events and knowledge.

The connection between recent memories and prior memories and knowledge is one reason you can wake up with a new and valuable perspective on a problem, even a complete solution, says Andrew E. Budson, PhD, of Harvard Medical School.

That’s exactly what happened to Dmitri Mendeleev, who struggled for months with how to arrange the atomic elements in the periodic table. In a dream on February 17, 1869, he glimpsed the locations of all the elements and, after writing down what he had dreamed, he only had to correct one small error.

REM sleep also helps with emotional processing. When you experience negative emotions, you often feel better when you wake up the next day, and you cope with difficult situations or experiences more easily.

REM sleep also helps with emotional processing.

However, sleep quality changes as we age. A study by Dr. Matthew Walker and colleagues found that people over 60 had 70% less deep sleep than younger people aged 18-25.

This involves slow-wave sleep . Slow waves are produced in an area of ​​the brain called the medial prefrontal cortex. The medial prefrontal cortex weakens over time, and as a result, older adults often experience less slow-wave sleep during their normal sleep cycle and have more difficulty processing memories.

Because memory decline is linked to reduced deep sleep, scientists are now investigating ways to increase deep sleep stages to improve memory in this group of older adults.

For young people, especially students, Dr. Stickgold emphasizes that staying up late to study will not be as effective as getting enough sleep before and after studying to enhance new memories and consolidate learned knowledge.