by Björn Rasch Department of Psychology, University of Fribourg, Switzerland
Björn Rasch PhD is a sleep researcher and biopsychologist who studies how sleep can modify cognitive behavior, learning and memory. He is also interested in how our thoughts and imaginations can affect sleep, for example by using hypnotic suggestions and relaxation techniques. His studies show that sleep and cognition are strongly related.
Sleep is good for memory. Although you might think that the brain is “shut off” during sleep, that description is inaccurate. The brain is active and helps us to memorize. Thus, when you study in the evening, don’t stay up all night, but stop at a reasonable hour and go to sleep. The next morning the memory of what you learned in the evening will be better after a good night’s sleep. If you like to study in the morning, that’s fine, too: feeling awake with high concentration also helps learning. Even so, if you repeat the material in the evening before going to bed, your memory will benefit additionally from the sleep that follows.
We do not fully understand why sleep helps us memorize. One research group recently proposed that sleep helps eliminate unnecessary, irrelevant connections in the brain. As a result, your memory of the study material appears clearer the next day because the irrelevant “noise” has been reduced by sleep. On the other hand it has been proposed that the learned material is actively repeated during sleep, a process called “reactivation” or “replay.” From this perspective, sleep offers an opportunity for the brain to train itself when it is disconnected from the outside world, a process called “offline learning.” Both accounts assume that deep sleep, which occurs mostly in the initial hours of nighttime sleep, is most important for these processes.
Deep sleep is characterized by very slow oscillation activity of brain neurons, creating repeated short intervals during which neurons are either very active or almost silent. The slow oscillation activity is thought to play an important role for memory, by reducing irrelevant connections or providing a space for memory replay — maybe both. In addition, faster sleep-specific brain oscillations — “sleep spindles” — may also be important for memory processing.
While many researchers agree that slow-wave sleep is important for strengthening memories, the role of rapid-eye movement sleep (REM) is less clear. REM sleep may be more involved in emotional and creative processing, though the evidence is less strong. Even less clear is the role of dreaming for memory. Dreaming occurs during all stages of sleep, not only REM sleep. Memory replay might influence dreams, or dreaming may influence replay. However, it does not seem necessary to dream about your study material — or to remember your dream about it — to show improved learning after sleep.
Unquestionably, sleep after learning helps you memorize. But can you learn completely new things while you are asleep? Recent studies suggest that you can. Listening to completely unknown information during sleep appears to be maintained to some degree in the morning. However, the effects appear rather small, and the practical relevance of the possibility of learning during sleep remains unclear.
Which brings us to the most important advice for studying: The most effective way to learn something is to study the material actively when you are awake. Active study means that you should not only “passively” read and repeat the information, but actively try to recall it. In other words, you need to test yourself repeatedly. And you should do this consistently over days and weeks. Do not try to learn everything for an exam all at once; that will not help remembering over the long term. By spreading your study over days and weeks, a good night’s sleep will help you to memorize. Think about the additional benefits of sleep for the immune system, metabolism and weight regulation, alertness and general wellbeing. It is well worth reserving sufficient time for sleep, to support not only your health but also your memory and academic success.