“Dreams are a form of therapy to help us cope with painful memories,” according to the Daily Mirror. The newspaper said scientists have found that during deep sleep the body’s “stress chemistry” shuts down to take the edge off the day’s problems.
The research looked at a type of sleep called Rapid Eye Movement (REM) sleep, the phase of deep sleep when dreams occur. In the small study, researchers exposed people to images designed to trigger an emotional response and looked at how the time of day they were viewed affected their emotions and brain activity. The researchers found that those participants who slept between viewings showed reduced activity in brain areas linked to emotion, and reported finding the images less intense.
This small study highlights some interesting theories as to why sleep may promote emotional wellbeing. Generally, it seems to support the commonly held belief that a good night’s sleep can put our worries and emotions in perspective. However, it only involved 34 participants, and looked at the short-term outcomes in an artificial setting. It would therefore be unwise to draw any firm conclusions from its findings, or to assume that sleep is therapy for traumatic experiences.
The study was generally overinterpreted by the press. In particular, the claims that dreams can help ease bad memories is not supported by its findings.
Where did the story come from?
The study was carried out by researchers from the University of California and was funded by the US National Institutes of Health. The study was published in the peer-reviewed journal, Current Biology.
What kind of research was this?
This was a randomised study of 34 healthy adults. It looked at the links between the dreaming stage of sleep, called REM sleep, and recent emotional experiences. It measured the effects REM sleep had on people’s emotions using a variety of methods, such as:
- subjective reports from the participants
- MRI scans of their brains
- recordings of electrical brain activity during REM sleep
The researchers say there is evidence that there may be a ‘potentially causal interaction’ between sleep and the part of the brain concerned with processing emotion and feeling.
The researchers point out that nearly all mood disorders involve sleep abnormalities, usually relating to REM sleep. They add that recent theories suggest REM sleep may reduce the brain’s reaction to recent waking emotional experiences, thus reducing their emotional intensity. They suggest it is done possibly by suppressing certain chemical messengers commonly implicated in stress and arousal.
What did the research involve?
The researchers recruited 34 healthy young adults aged between 18 and 30 years. They were randomly divided into two groups that were put through emotional response tests but at different times during the day. In these tests all participants were shown 150 ‘emotional’ images, which were taken from a standardised picture system designed to test emotional reaction (the study provides no detail as to what these images might portray).
Participants viewed the images twice, 12 hours apart. After each viewing they were asked to rate the subjective emotional intensity of the images on a 1-5 scale, with the higher numbers corresponding to increasing intensity. At the same time as they took these tests, an MRI scanner measured brain activity.
Participants in one group viewed the images in the morning and again in the evening, staying awake between the two viewings. The other group viewed the images in the evening and again in the morning after a full night’s sleep. Researchers also recorded the electrical brain activity of the second group while they slept, using electroencephalograms (EEG).
What were the basic results?
The researchers observed a number of differences between the two groups, which differed in brain activity, subjective ratings of the images and EEG recordings.
From the MRI scans they found changes in the activity in the part of the brain called the amygdala, a small, almond-shaped part of the brain thought to be involved in processing emotion. They found that:
- In the group that had slept overnight between viewings of the images, activity in the amygdala was significantly reduced between the first and second viewings.
- In the group who viewed the images without sleeping overnight, activity in the amygdala increased significantly between the first and second viewings.
- These differences were also associated with changes in activity in part of the brain called the ‘ventromedial prefrontal cortex’ (vmPFC), part of the brain associated with cognitive functions such as making decisions.
- Between the two viewings, the sleep group showed an increase in vmPFC activity, while the awake group showed a reduction in vmPFC activity.
From the subjective ratings of the images, participants who had slept overnight between the viewings gave less intense ratings to the images and more ‘neutral ratings’ on their second viewing, while those who had both viewings during the day showed no decrease in ratings for emotional intensity.
Finally, they found that in the sleep group, recordings of electrical brain activity showed that certain patterns of electrical activity decreased during REM sleep. They say this is a marker for reduced ‘adrenergic’ activity (brain activity associated with substances such as adrenaline).
How did the researchers interpret the results?
They say the experiment shows that REM sleep acts on the central nervous system to decrease the emotional intensity of previous experiences. It is possible, they say, that the disruption of REM sleep in certain psychological disorders, such as post-traumatic stress disorder, may make it difficult for people to recover. It may also explain why treatments that suppress brain activity at night may be successful in this type of disorder.
This small study puts forward some interesting theories as to why sleep may promote emotional wellbeing. It seems to support the commonly held and commonsense idea that a good night’s sleep can help people get their worries and emotional reactions in perspective. A regular healthy sleep pattern may also help those with anxiety and other disorders.
However, it should be noted that the study only involved 34 participants, that it only looked at the possible effects of sleep on specific emotional stimuli and that it was conducted over a 12-hour period. It would therefore be unwise to draw any firm conclusions from its findings. Although its findings are of interest to scientists in the field of sleep disorders, it is not possible to draw any conclusions about sleep as therapy.
In addition, the study was not blinded, which means both researchers and participants knew which group participants were in. So it is possible that the reactions of people in the sleep group were affected by the knowledge that they had slept, rather than by sleep itself.
Nor does anything in the study show that dreaming specifically has a beneficial effect. It is possible that achieving deep sleep, rather than having dreams, was responsible for the possible changes in brain activity and also the reactions that researchers recorded.
Analysis by Bazian
Edited by NHS Website
Links to the headlines
BBC News, 24 November 2011
Daily Mirror, 24 November 2011
Daily Mail, 24 November 2011
Links to the science
Current Biology, November 23 2011