A study finds sleep deprivation makes unwelcome thoughts occur more frequently and makes them harder to manage.

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It’s not uncommon for unwelcome thoughts to cross a person’s mind now and again.

According to psychologist Marcus Harrington of the Department of Psychology at the University of York in the United Kingdom, “For most people, thought intrusions pass quickly, but for those [who are experiencing] psychiatric conditions, such as post-traumatic stress disorder (PTSD), they can be repetitive, uncontrollable, and distressing.”

Harrington is the lead author of a new study investigating the effect of sleep deprivation on unwanted thoughts.

The study finds that sleep deprivation increases the frequency of unwanted thoughts and lessens an individual’s ability to control them.

Funded by the Medical Research Council, the research appears in Clinical Psychological Science.

“In everyday life,” says Harrington, “mundane encounters can remind us of unpleasant experiences. For example, a car driving too fast on the motorway might cause us to retrieve unwanted memories from a car accident many years ago.”

However, for people with some psychiatric disorders, unwelcome thoughts can be a frequent, persistent, and often emotionally destructive intrusion.

“It is clear,” says Harrington, “that the ability to suppress unwanted thoughts varies dramatically between individuals, but, until now, the factors that drive this variability have been mysterious. Our study suggests sleep loss has a considerable impact on our ability to keep unwanted thoughts out of our minds.”

A lack of sleep and the resulting inability to manage unwelcome thoughts may also be self-perpetuating.

“The study also suggests that the onset of intrusive thoughts and emotional disturbances following bouts of poor sleep could create a vicious cycle, whereby upsetting intrusions and emotional distress exacerbate sleep problems, inhibiting the sleep needed to support recovery.”

– Senior author Dr. Scott Cairney

The researchers recruited 60 healthy individuals with an average age of 20 to participate in the study. The researchers randomly assigned them to a sleep group or a sleep-deprivation group. There were 30 participants in the sleep deprivation group and 29 in the sleep group because the researchers disqualified one participant.

The participants had to forego naps, caffeine, and alcohol on test days.

The researchers trained each person to associate face photos with either negative or neutral images from the International Affective Picture System. The participants also learned suppression techniques to help them overcome unpleasant memories. After their training, they went to sleep for the night.

The following day, participants were shown faces and asked to try and suppress the associations the faces provoked.

People who had sufficient sleep could successfully suppress unwelcome thoughts and reported that doing so became easier over time.

The participants also reported a reduction in their emotional response to negative images. Researchers supported this with observations of a reduction in their sweat response as they viewed the images.

Individuals from the sleep-deprivation group reported having a difficult time suppressing their thoughts. They also reported that experiencing and then managing intrusive thoughts remained a challenge throughout the study.

Participants who were sleep-deprived reported a 50% increase in unwanted thoughts compared with those who were well-rested.

The authors write:

“Even after sleep-deprived participants initially gained control over unwanted memories and prevented them from intruding, they were consistently more susceptible to relapses when reminders were confronted again later compared with rested individuals.”

The study mentions a caveat. Since scientists know that sleep helps solidify pre-bedtime memorization, perhaps those deprived of sleep could not utilize the memory suppression techniques they learned the night before as the sleep group could.

Says Cairney:

“This study offers an important insight into the impact of sleep on mental health. Besides post-traumatic stress disorder and depression, our findings might have implications for our understanding of other disorders linked to sleep disturbances, such as obsessive-compulsive disorder and schizophrenia.”