Thursday July 2 2015
Sleep may consolidate traumatic events into long-term memories
"Staying awake may be the best way to stop disturbing flashbacks," the Daily Mail reports. A small psychological experiment carried out at Oxford University suggests that sleep could possibly help embed traumatic events in the memory, in some cases.
The study involved 42 students, half of whom were randomly assigned to sleep deprivation and the other to sleep at home as usual. They all watched a 15-minute film compilation of distressing clips of simulated events such as suicides and injuries. Both groups had a drop in mood after watching the clips. Over the next six days, those who were not allowed to sleep had on average 2.3 "flashbacks" while the sleep group had 3.8 flashbacks.
The small amount of study participants and the experimental study design mean that the results would (or should) not lead to changes in current clinical advice for people affected by trauma. But if the results are replicated in larger populations, then it could mean that the common practice of giving sedatives to people affected by trauma to help them sleep, could be doing more harm than good.
It you are troubled by intrusive thoughts or images following a traumatic event, for four weeks or more, then you may be at risk for post-traumatic stress disorder (PTSD). We recommend you contact your GP for an assessment.
If symptoms persist, treatments such as cognitive behavioural therapy can often help.
Where did the story come from?
The study was carried out by researchers from the University of Oxford, the MRC Cognition and Brain Sciences Unit in Cambridge and the Karolinska Institute in Sweden. It was funded by the Wellcome Trust and the National Institute for Health Research.
The study was published in the peer-reviewed medical journal Sleep.
The study was widely covered in the UK media but none of the reporting explained any of the limitations of this study.
Also The Daily Telegraph did not provide details of the actual number of flashbacks experienced, but instead reported that the sleep-deprived group had around 40% fewer flashbacks. This sounds like a much more dramatic difference than the actual figures reported in the study (3.8 compared with 2.3).
Finally, the Daily Mirror’s headline that sleeping "could actually cause flashbacks" is unsupported by the results provided by the study.
What kind of research was this?
This was a small, non-blinded randomised controlled trial that aimed to see if sleep deprivation could reduce intrusive images (flashbacks) and memories following a traumatic event.
What did the research involve?
Forty-two healthy students aged 18 to 25 were paid to participate in the research. They completed questionnaires before the study commenced to ensure that they had regular sleeping patterns and no personal or family history of mental health problems. None smoked and none were taking any medication other than the contraceptive pill. They were randomly split into two groups, 20 in a "sleep deprived" group (14 females) and 22 in the "sleep" group (15 females).
On the first day of the study the volunteers completed assessments to measure their mood (visual analogue mood scale (VAS)) and a level of detachment from their surroundings (dissociative state scale (DSS)) before and after watching a "trauma film" in the evening. The trauma film was a 15-minute compilation of distressing clips from films and TV adverts including a suicide, bullying, injury and cutting of the face. The students had consented to watch distressing images and were instructed to imagine that they were at the scene, watching it happen. They were told they could stop the film at any time but none of the students chose to do so.
The sleep group went home and were allowed to sleep as usual but were asked not to watch TV or listen to music. The sleep deprived group were kept awake until 7pm the following day in a sleep laboratory with researchers keeping them awake. They were allowed to play board games, read, talk to researchers and walk about. They were not allowed to use computers, TV, DVDs, music or to leave the laboratory. They had access to a sandwich or fruit every two hours and could have a shower in the morning.
In the morning, both groups were assessed for the impact of the film using the well-validated Impact of Event Scale – Revised (IES-R). This is a 22-item assessment for post-traumatic symptoms such as intrusive memories, avoidance of distressing stimuli and increased alertness. It gives a range in score from 0 (no symptoms) to 88 (disabling symptoms). They were then asked to keep a diary of any intrusive memories over the next six days and rate their distress from the memory.
What were the basic results?
Both groups experienced the same level of negative mood and feeling of detachment immediately after watching the film.
On day one, the sleep deprived group had a lower score on the IES-R than the sleep group (8.47 versus 11.52).
Over the next six days, the sleep deprived group reported fewer intrusive memories or disturbing images than the sleep group (mean 2.28 intrusive memories per person versus 3.76).
How did the researchers interpret the results?
The authors concluded that their "findings suggest that sleep deprivation on one night, rather than sleeping, reduces emotional effect and intrusive memories following exposure to experimental trauma".
As the researchers acknowledge, the results of this study are interesting, but it is important to stress that the study was based on a small experimental model of trauma through watching a film with "traumatic content". This is quite different to many real-life experiences that cause PTSD. The participants will have known that the film was not real, which is different to experiences of violence or perceived threat in reality. The number of flashbacks was also very low – on average two to four per person during the whole six days after the film – compared with that which would be experienced by people with PTSD.
Strengths of the study include the use of watches to ensure that naps were not taken during the day by either group and they did not use alcohol or caffeine during the study.
However, there are several limitations including:
- Staying in the laboratory with other participants and the researchers may have had a confounding effect on the results as participants could have talked through the films and images, which might have helped.
- The study only looked at short-term effects over a period of six days.
- None of the sleep group reported any problem in sleeping, whereas in real-life situations following a traumatic event, people are often unable to sleep or have disturbed sleep.
- The study is based on small numbers of participants, which reduces the reliability of the results.
- The results may not be generalisable to the wider population as the study participants were all students and were happy to be included in the study with the knowledge that they would be exposed to distressing images.
- The study is reliant on self-report of intrusive memories.
The results of the study are not conclusive enough to advise that staying awake after trauma will reduce the chance of PTSD, whether with people or alone. Further studies along this line would be required before official advice could be changed.
It is normal to experience upsetting and confusing thoughts after a traumatic event, but in most people these will improve naturally over a few weeks.
You should visit your GP if you or your child are still having problems about four weeks after a traumatic experience, or if the symptoms are particularly troublesome. Read more about post-traumatic stress disorder.