Rumination, worry, and negative thoughts disturb our sleep, making them key targets for psychological interventions. Especially during the sleep onset period, negative thinking increases our state of arousal, keeping us awake. Negative thoughts during the night can awaken us, causing significant distress. But even if we can stay asleep, negative dream content will decrease sleep quality and increase the likelihood of awakenings.
In a recent study, we asked healthy participants purposely to sleep worse than normal, but without instructing them how to do so. Sleep was measured using polysomnography. Participants could worsen their sleep quality simply by wanting to do so. They extended their time to fall asleep and woke up significantly more often compared to the normal control night. When we asked them how they worsened their sleep, they reported that they actively produced negative thoughts and worry.
While the role of negative thoughts in sleep disturbances is well known, it remains quite unclear how this works. During waking, we can assume that negative thoughts increase physiological arousal, which counteracts the relaxation required for sleep onset. But once we have fallen asleep, how do negative thoughts increase awakenings? We can assume that the negative thinking persists during the sleep despite reduced consciousness. They become a focus of mental activity, influencing dream content, and possibly even triggering nightmares.
On the other hand, can positive thinking improve sleep? In another recent study healthy young participants slept twice in our laboratory. On one night they were presented with positive words (such as “relax”, “easy”, “pleasant”) played at very low volume to avoid awakenings. On the control night they were presented with neutral words unrelated to sleep (such as “material”, “rocks”, “copper”). When asked the next morning, they could not say which type of word had been presented. Still, on the “positive” night, with presentation of relaxing words, they spent significantly more time in deep sleep, and reported better subjective sleep quality and higher alertness the next morning. It appears possible to bias our mental activity during sleep-inducing relaxation and promote subjective sleep quality and recovery.
This word-presentation technique may have promise for people with sleep difficulties — even for those with diagnosed insomnia — but will require testing in clinical populations. The method should be individually personalized using words or sounds best suited to induce relaxation and feelings of safety. The patient should join in specifying the preferred voice type, manner of speaking, etc.
Active thoughts during sleep may prove to be a causal factor for better or worse sleep quality and contribute to non-pharmacologic treatment methods with wide benefit for subjective sleep quality, even when objective measures are inconsistent. This approach is like long-established methods used by many people, as they listen to calming music or whispering sounds — effective folk remedies with a solid empirical basis.
“DEEP” SLEEP AND MEMORY FORMATION
Sleep also helps form and preserve memory. Although you might think that the brain shuts off during sleep, that would be wrong. The brain remains active and helps us memorize. When you study in the evening, for example, the principle is not to 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 significantly better. If you like to study in the morning, that’s fine, too: feeling wide awake with high concentration is certainly beneficial. But you can enhance the benefit by repeating the material in the evening. The sleep that follows will enhance your memory.
We do not fully understand how sleep helps us memorize. One research group has proposed that sleep eliminates unnecessary, irrelevant connections in the brain. As a result, memory is clearer the next day because the irrelevant “noise” was reduced by sleep. Another view is 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. This process is called “offline learning.”
Both explanations assume that deep sleep is most important for memory formation. Deep sleep is characterized by very slow oscillation activity of brain neurons, producing short intervals during which the neurons are alternately very active or almost silent. These oscillations, according to the theory, play an important role by reducing irrelevant connections or providing an opportunity for memory replay — maybe both. Faster oscillations — called “sleep spindles” — may also be important for memory processing.
REM SLEEP
While researchers generally 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 weaker. How dreaming affects memory is even less clear. Dreaming occurs during all stages of sleep, not only REM sleep. Memory replay might influence dreams, or dreaming may influence replay. However, it is clearly unnecessary to dream about your study material — or to remember your dream about it — to show improved learning after sleep.
LEARNING WHILE ASLEEP
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 novel information during sleep appears to be maintained to some degree in the morning. However, the influence is small, and any practical value of learning during sleep remains unclear.
LEARNING WHILE AWAKE IS KEY
Which brings us to the most important advice: 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, test yourself repeatedly and consistently over days and weeks. Do not try to cram for exams — there is no long-term advantage. By spreading your study over days and weeks, good nights of sleep will help you memorize. Furthermore, better memory is not the only advantage! Good sleep provides additional benefits for the immune system, metabolism and weight regulation, alertness, and general wellbeing. These multiple benefits will support not only your health but also your memory and academic success.
Björn Rasch PhD, Department of Psychology, University of Fribourg, Switzerland, is a biopsychologist who studies how sleep can modify cognition, learning and memory. He is also investigating methods to improve sleep by hypnotic suggestion and relaxation techniques.
