Memory and sleep: Techniques to consolidate memory during slumber

Evan Walker
Evan Walker TheMediTary.Com |

Scientists now know that while we snooze, our brains help solidify the memories we made during the day. In this Special Feature, we investigate whether simple techniques might help improve memory retention during the night.

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Can sleep techniques enhance our memory? Image credit: Hanna Shot/Stocksy.

It is almost too obvious to repeat, but the brain is an immensely complex organ. Billions of cells form trillions of connections, all communicating via drips, ripples, and waves of neurotransmitters, hormones, electrical impulses, and other signaling molecules.

Getting a clear sense of what happens inside the brain, why it happens, and its importance to the human experience are monumental challenges.

Despite the odds, neuroscientists continue to forge ahead. And they have made incredible progress over recent decades. Some of these brave souls investigate a particularly difficult-to-study topic: sleep.

Although every human who has ever lived on Earth has experienced this phenomenon, sleep is still shrouded in a duvet of mystery. We do not understand the full story, but it is now clear that one of sleep’s roles is to solidify, or consolidate memories.

In this Special Feature, we explore practices that might help us improve our memory skills.

But before we delve into experimental memory-enhancing techniques, we will briefly outline how memory consolidation works during sleep.

Scientists believe that during waking hours, our brains are primed to make or “encode” new memories. But during sleep, our brains switch to consolidation mode.

When you first learn something during the day, your brain lays down a “memory trace.” Initially, this trace is particularly susceptible to disturbances. In other words, it is easy to forget.

Then, during sleep, this memory is consolidated — the memory trace is stabilized.

On a cellular level, memories are formed by changing the strength of synaptic connections in a network that represents a memory. During sleep, synapses — the connections between brain cells — are remodelled, producing permanent changes that solidify the memory trace, helping create longterm memories.

Researchers are still unpicking the precise processes, but it seems that during sleep, the hippocampus — an important brain region involved in memory“replays” the memory. This helps the memory trace and its associated network of neurons make permanent changes.

For the rest of this article, we will investigate ways in which you might enhance your memory storage using sleep. After all, as the authors of a paper published in Scientific Reports in 2020 write, “[e]ffortless learning during sleep is everybody’s dream.”

To be clear, though, most of the studies we mention below are small, and because this is a relatively niche field, some of the research is quite old, so we have to remain critical.

However, some of the techniques we cover are relatively simple and safe. They may be worth trying if you are cramming for an exam, learning something new for work, or simply trying to keep your memory in tip-top shape as you age.

Researchers have shown that going to sleep shortly after learning something helps the brain consolidate declarative memories more efficiently.

Declarative memory is defined as remembering events and facts, such as the name of your friends and what you ate last night.

In one study, researchers asked participants to learn word pairs. They found that people who went to sleep shortly after the task performed better 24 hours later than those who did not sleep until longer after the task.

Another study, which involved high school students learning new vocabulary had similar results: Those who went to sleep just a few hours after learning retained memories better than those who went to sleep many hours after learning.

Now, it is not practical to simply go to sleep after learning something new, especially if you learn it first thing in the morning. Perhaps running over new learnings just before you go to sleep might help cement them during slumber.

Sleep is vital for good health — not just memory, and experts agree that humans need around 7–9 hours each night, although there is much variation between individuals.

When it comes to sleep and memory, though, a daytime nap might be enough to make a difference.

According to some research, even a few minutes of shuteye is enough to improve memory performance. One study found that 90-minute naps were more effective than 40-minute naps.

Studies do not always agree, but overall, naps might be a useful tool for some people. For instance, a review of 22 studies boldly concludes that: “Daytime napping is effective on declarative memory performance in healthy adults.”

Although nothing beats a full night of sleep, an occasional tactical nap may help you retain information.

Studies hint that the consolidation process that happens during sleep may prioritize memories that are more relevant to the future. This makes logical sense — the brain cannot remember every little thing that happened in the day, so it has to choose what to store.

In one study, for instance, researchers asked participants to learn pairs of words. They informed some participants that there would be a test the next day. They found that those who slept before the test performed better than those who did not, but only if they knew about the test.

Perhaps providing oneself with an incentive might enhance memory consolidation overnight.

Again, though, not all studies agree. The authors of a review explain that studies on the topic have produced “highly mixed findings.”

Medical News Today spoke with one of the authors of the review, Per Davidson, a senior lecturer of psychology at Kristianstad University in Sweden.

He explained that “we don’t really know exactly what happens during sleep that consolidates memory, so it is difficult to say how we should manipulate sleep to enhance this consolidation.”

Olfaction — our sense of smell — is tightly connected to parts of the brain important for memory and emotion. Many of us have probably experienced this in action: When we smell an odor and it instantly sparks a memory or emotion.

Some scientists have investigated whether odors might be a useful way to cement memories and improve memory recall.

One study tested this relationship in a real-life situation. The researchers asked pupils to keep rose-scented sticks near them as they learned vocabulary at home. A week later, they sat an exam at school.

The scientists split the 54 students into four groups:

  1. no exposure to rose scent
  2. exposure to rose scent during learning and the test
  3. exposure to rose scent while learning and every night but not during the test
  4. exposure to rose scent while learning, every night, and during the test.

They found that participants in groups 3 and 4 performed best. They increased their learning success by around 30% when the aroma was used during both the learning and sleeping phases.

In a follow-up study in 2023, scientists generated similar results — those who experienced the rose odor during learning, sleep, and testing performed better on a vocabulary test.

These were relatively small studies, so we have to be cautious about interpreting the results. Once again, though, this is a fairly easy technique to try, so it may be worth experimenting.

One could keep a distinctive odor next to them only when they are learning and sleeping. It might just provide an edge.

Beyond olfaction, other researchers have investigated whether other types of stimuli, including sound, might help consolidate memories during sleep.

In one study, researchers investigated whether classical music might be a useful tool to improve memory consolidation.

MNT contacted one of the study’s authors, Michael K. Scullin, PhD, associate professor of psychology and neuroscience at Baylor University in Waco, TX. We asked why they chose classical music.

“We chose classical music so as not to interfere with initial learning. When people listen to lyrical music while studying, the singing can interfere with their cognitive processing,” he explained.

The scientists played classical music with distinctive melodies during a microeconomics lecture. That night, during slow-wave sleep, the researchers either played the students the same music or white noise.

Those who heard classical music as they slept performed better on the test than those who heard the white noise. Interestingly, the effect seemed to be more pronounced in females.

For anyone who wants to try this technique at home, playing classical music only during slow-wave sleep could be a problem.

However, Scullin has a workaround; he told us that “people might be able to play the music mainly during their slow-wave sleep if they could hit play at bedtime but change the first 30–40 minutes of the track to being white noise.”

Still, he also explained that even this might not be necessary:

“I came across a review article on the topic and was happy to see that one study did use [a similar intervention] all night long and still found benefits. More work is needed, but maybe it’ll turn out to not be that critical that the stimulus is presented only in slow-wave sleep.”

Scientists are still investigating this effect, and many factors are likely to influence how well this approach works, including the type of memory, the type of stimulus, and what phase of sleep the participant is in when they experience the stimulus.

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