The dream of effortlessly learning while sleeping is shared by many. One of the functions of sleep is to consolidate memories from the day.
While everyone sleeps, this physiological phenomenon remains shrouded in mystery. Despite the challenges, neuroscientists continue to make strides. Over the past few decades, incredible progress has been made in this field, with one particularly challenging topic being the role of sleep in memory.
Brain Shifts to Consolidation Mode During Sleep
While awake, the brain is primed to create or “encode” new memories. However, during sleep, the brain shifts to consolidation mode.
When you learn new information during the day, the brain forms memory traces. Initially, these traces are particularly susceptible to interference, meaning they are easily forgotten. Then, during sleep, these memory traces are consolidated and stabilized.
At the cellular level, memories are formed by changing the strength of synaptic connections within networks representing those memories. During sleep, synapses (connections between brain cells) are reshaped, resulting in permanent changes that consolidate memory traces and help create long-term memories.
Sleeping Shortly After Learning Aids Memory
Declarative memory, defined as remembering events and facts like a friend’s name or what you ate last night, is more effectively consolidated if one sleeps shortly after learning new information.
Psychologists at the University of Notre Dame in the United States asked participants to learn pairs of words. The results showed that those who slept shortly after the learning task performed better on a test 24 hours later than those who slept long after the task. Similarly, neuroendocrinologists at the University of Lübeck in Germany asked high school students to learn new vocabulary and obtained similar results: students who slept shortly after learning retained better memory.
Does Napping Aid Memory Consolidation?
Sleep is crucial for overall health, not just memory. Experts agree that most adults need 7-9 hours of sleep per night, although there is considerable variation among individuals.
When it comes to sleep and memory, taking a nap during the day can be helpful. Experimental psychologists at the University of Düsseldorf in Germany found that even napping for a few minutes was enough to enhance performance in declarative memory tasks. Neurobiologists at the University of Tübingen in Germany found that a 90-minute nap was more effective than a 40-minute nap in memory consolidation.
Although research results in this area are not always consistent, napping generally helps some people consolidate memories. For example, sleep physicians at Kerman University of Medical Sciences in Iran conducted a systematic review of 22 studies and concluded that daytime napping effectively improves performance in declarative memory tasks among healthy adults.
Therefore, while a full night’s sleep is more effective for memory consolidation, occasional tactical napping can also help retain information.
Providing Cues Aids Memory Consolidation During Sleep
Research indicates that the consolidation process during sleep prioritizes memories relevant to the future. This makes sense logically, as the brain cannot remember every little thing that happens in a day, so it must select which information to store.
For example, neuroendocrinologists at the University of Lübeck in Germany asked participants to learn pairs of words. They told some participants that there would be a test the next day. The results showed that those who slept before the test performed better than those who didn’t, but only if they knew about the test. In other words, providing cues aids memory consolidation.
The Role of Smell in Memory
Physiologists at New York University School of Medicine found a close association between smell and brain regions important for memory and emotion. Many people have experienced the phenomenon where a certain smell immediately triggers a memory or emotion, leading some scientists to investigate whether smell aids memory consolidation and enhancement.
Psychologists at the University of Freiburg in Germany tested this relationship in real-world settings. They asked 54 students to study new vocabulary words at home with rose-scented branches nearby. A week later, they took a test at school. The results showed that students who smelled roses during learning, sleep, and testing performed better. Specifically, their success rate in remembering new vocabulary improved by 30%. Since using scent is relatively easy, it’s worth trying.
The Role of Music
In addition to smell, researchers have explored other types of stimuli, including sound, to determine if they aid memory consolidation during sleep.
For example, psychologists at Baylor University in the United States investigated whether listening to classical music aids memory consolidation. Classical music was chosen to avoid interference with learning.
If people listened to lyrical music while studying, the lyrics might interfere with their cognitive processes. Researchers played classical music with a unique melody during a microeconomics lecture. That night, during slow-wave sleep, researchers either played the same music or white noise for students. The results showed that students who listened to classical music while sleeping performed better on tests than those who listened to white noise. Interestingly, this effect was more pronounced in females.
How to Improve Sleep Quality for Memory Consolidation
While many mysteries remain in the field of sleep, one thing is clear: sleep is crucial for memory consolidation and many other essential functions.
To improve sleep quality for memory consolidation, consider the following strategies:
- Prioritize sleep as a top priority.
- Establish good sleep habits by going to bed and waking up at the same time every day.
- Create a conducive sleep environment by adjusting the temperature and light in the bedroom, and avoiding electronic devices two hours before bedtime.
- For students, the best approach is to use effective learning strategies when awake and then get a good night’s sleep.
