Sleep and Memory: How They Work Together
“Sleep on it.” We’ve long known that a good night’s sleep confers important benefits on mood, alertness, concentration, and judgment. Research over more than a century has also established that sleep plays an important role in memory retention. More recently, studies have begun to establish more precisely how the connection between sleep and memory works. “Sleep and memory are both mysterious,” says psychiatrist and sleep specialist Dr. Alex Dimitriu. “Exciting research is being done to unearth the secrets of the connection between them. We’ve known that the quantity and quality of sleep affect our ability to learn and remember in two ways. First, adequate sleep enables us to concentrate so we can learn efficiently. Then, sleep itself is needed to consolidate memories of what has been learned. Now neuroscientists are learning how different facets of memory and different stages of sleep work together.”
There are three necessary steps for memory to function properly: acquisition occurs when we learn or experience something new; consolidation is the process that stabilizes the new information in the brain – makes it stick; and recall is the ability to access the information after it is stored. Acquisition and recall occur when we are awake, consolidation while we sleep. “When we are awake,” says Dr. Dimitriu, “our brains are optimized to react to external stimuli and encode new memories that are, at that point, unstable and subject to forgetting. The sleeping brain, with greatly reduced exposure to external stimuli, provides optimal conditions for the consolidation processes that strengthen and integrate the new memory into existing knowledge networks for long-term storage.”
“At one time,” says Dr. Dimitriu, “it was thought that sleep played a passive role in enhancing memory by protecting it from interference by external stimuli. Now we know that sleep plays a more active role. It was also thought that rapid-eye-movement (REM) sleep played the primary role. Now we know that slow-wave sleep (SWS) plays an important role in consolidating memories. Scientists now believe that different kinds of memories are processed during different stages of sleep.”
The stages of sleep alternate in a cycle over the course the sleep period. SWS, which is deep, restful sleep, is predominant during the early part of the cycle and then decreases in intensity and duration; REM sleep, when dreaming most frequently occurs, becomes more intense and longer-lasting toward the end of the sleep period. While the relationship between types of memory and sleep stages is complex, some studies have suggested that declarative memory, which is fact-based – what we know – benefits primarily from sleep periods dominated by SWS and procedural memory – remembering how to do something – is related to REM sleep.
“There’s a lot we don’t know about the relationship between sleep and memory,” says Dr. Dimitriu. “But we know that adequate sleep will improve concentration to help you learn and will help you remember what you’ve learned.” Dr. Dimitriu offers these suggestions for improving the quantity and quality of sleep:
- Exercise early in the day, not within several hours of bedtime.
- Reduce or eliminate stimulants such as caffeine and nicotine during the day and alcohol in the evening.
- Avoid naps or limit them to 30 minutes; don’t nap after 3:00pm.
- Stick to a sleep schedule, going to bed and waking at the same time each day, including weekends.
- Relax and clear your mind before bedtime – read a book, listen to quiet music, take a hot bath
- Keep your room cooler than during the day. Use a fan or noise machine to mask distracting sounds. Try room-darkening shades if morning light is waking you too early.
- Consider changing your mattress and bedding if it’s more than 5-8 years old. Bed, mattress and pillow are important to quality sleep and eliminating back pain.
- Don’t eat a heavy meal or drink a lot of liquid close to bedtime.
- Increasing exposure to sunlight or bright light during the day can improve sleep at night.
- The opposite is true at night. Don’t use a computer, tablet or smart phone right before going to bed! The light from the screen stimulates the brain and makes it hard to fall asleep.
Alex Dimitriu, MD, is double board-certified in psychiatry and sleep medicine and is the founder of the Menlo Park Psychiatry & Sleep Medicine Center in Menlo Park, CA.