Sleep deficiency may impair the ability to cognitively filter intrusive memories and thoughts when confronted with reminders of them, according to a recent study published in Clinical Psychological Science.1,2

Among the general population, people have varying ability to suppress memory intrusions. For many, memories of unpleasant experiences and thoughts can intrude conscious awareness when they are confronted with reminders of them in their daily lives.1

There are also certain psychiatric conditions associated with unwanted thoughts, such as post-traumatic stress disorder, major depressive disorder, obsessive compulsive disorder, and schizophrenia. Individuals with these conditions may typically experience a disproportionate amount of unwanted memory intrusions, with difficulties in their ability to limit the duration and recurrence of these intrusions. In turn, these intrusions can exacerbate the negative mood and affective dysregulation that the individual may be experiencing.1

Currently, the source for the variation around skill in suppressing intrusive memories is unknown, according to the study. Yet, the potential for the inhibition of intrusive memories playing a fundamental role in supporting mental health and well-being makes understanding the source of critical interest. For this reason, the researchers sought to test the hypothesis that sleep is required to successfully control memory intrusions.1

Among the study participants, the researchers tested whether total sleep deprivation or overnight sleep would affect participants’ ability to suppress intrusions of emotionally negative and neutral scenes when confronted with reminders. The researchers found that the sleep deprived participants suffered an increase in intrusive memories of nearly 50% compared with participants who had a full night sleep.1,2

"In everyday life, 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. For most people, thought intrusions pass quickly, but for those suffering with psychiatric conditions such as post-traumatic stress disorder, they can be repetitive, uncontrollable, and distressing,” said lead author Marcus Harrington, PhD, a research associate in the Department of Psychology at the University of York, in a press release.2

Harrington explained that it has been clear for many years that the ability to suppress unwanted thoughts varies dramatically between individuals.2

"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," Harrington said in the press release.2

During the study, the researchers taught 60 participants to associate faces with photographs of emotionally negative scenes, such as a war zone, or neutral scenes, such as a cityscape.1,2

The next morning, both the participant groups who were sleep deprived and who slept overnight were shown the same faces as the previous day. They were asked to try to suppress memories related to the scenes with which they were originally associated the day before.1,2

Patients who were sleep deprived were found to have much more difficulty suppressing unwanted thoughts of both the emotionally negative and neutral scenes from their conscious awareness. Although the task became progressively easier with practice for those participants who had slept the night before, those who had gone without sleep had a high occurrence of intrusive memories.1,2

The researchers also observed that the rested participants were able to view the negative scenes more positively after the suppression task and they also had a reduced sweat response when confronted with the negative scenes. However, the failure by the sleep deprived participants to filter intrusive memories was also found to correlate with a lack of a positive change in their association with the negative scenes.1,2

The authors noted that such findings raise the potential for sleep deprivation to disrupt prefrontal control over medial temporal lobe structures, which supports both memory and emotion. Such an occurrence would indicate the critical role sleep disturbance has in maintaining and exacerbating psychiatric conditions characterized by persistent and intrusive memories and thoughts.1,2

"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,” said senior author Scott Cairney, PhD, a postdoctoral research associate in the Department of Psychology at the University of York, in the press release. "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.”2

REFERENCES
  1. Harrington MO, Ashton JE, Sankarasubramanian S, Anderson MC, Cairney SA. Losing Control: Sleep Deprivation Impairs the Suppression of Unwanted Thoughts. Clinical Psychological Science. 2020. doi: 10.1177/216770262095151
  2. Study reveals role of sleep deprivation in unwanted thoughts. York, UK: University of York; October 20, 2020. eurekalert.org/pub_releases/2020-10/uoy-srr102020.php. Accessed November 6, 2020.