January 9, 2025
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Here’s why poor sleep and toxic thinking go hand in hand
The findings reveal memory-related brain processes that generate unwanted thoughts when people are sleep-deprived
Imagine you’re attending a friend’s housewarming party and — in front of everyone — you spill a glass of red wine on their new white couch. You are so angry that every time you see this friend, you immediately think of the mishap on the sofa.
Research has shown that how you react to that unwanted memory will depend on how well you sleep. If you are well rested, your brain will be able to quickly get rid of the negative memory. But if you’re someone who suffers from insomnia, intrusive thoughts about what happened—and the accompanying unpleasant emotions—will likely continue to bother you for a while.
Now a new study has been published Proceedings of the National Academy of Sciences of the United States of America it clarifies exactly what it is it goes wrong in the sleep-deprived brain when such unwanted thoughts enter. “This could be an important piece of the puzzle in understanding why people with chronic sleep deprivation are at high risk of developing mental health problems,” says Scott Cairney, associate professor of psychology at the University of York in England. and principal author of the findings.
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Cairney and his colleagues appeared an earlier study that sleep deprivation impairs people’s ability to suppress unwanted thoughts. But the team wanted to take those behavioral observations “a step further,” he says. “What’s really going on under the hood, in the brain, when people don’t get enough sleep?”
Previous studies have shown that when retrieving memories of past events, the hippocampus and another part of the brain, the right dorsolateral prefrontal cortex (rDLPFC), are responsible for suppressing this retrieval process. Cairney and his colleagues hypothesized that sleep deprivation impairs the rDLPFC’s ability to take “breaks” during recovery processes, he says.
To test this, the researchers recruited 85 students. First, the group was trained to associate images of neutral faces with specific scenes, some of which were negative, such as a car accident or a fight. “They form a rich association between the face and the scene, so when you present them with a face in isolation, their brain will automatically engage in a retrieval process,” says Cairney.
The researchers then divided the participants into two groups. One group had to stay up all night and the other was allowed to sleep on laboratory beds. Participants in the latter group were monitored for how much time they spent in rapid eye movement (REM) and non-REM sleep.
In the morning all participants were shown images of previously trained faces, but this time, participants had to think about the memory they had been trained to associate with the face or to delete it. During this task, their brain activity was measured using a functional magnetic resonance imaging (fMRI) scanner.
The results confirmed the belief of Cairney and his colleagues. Compared to participants who slept, those who stayed awake throughout the night had significantly reduced rDLPFC activity when they had to suppress intrusive thoughts. In contrast, hippocampal activity increased, probably because the rDLPFC did not turn off the retrieval process that was going on. This finding showed that sleep deprivation doesn’t cause a general decline in brain activity, Cairney says, but it appears to specifically affect it. certain parts of the brain involved in executive function.
Of the participants who had slept the previous night, the researchers also found a significant positive correlation between time spent in REM sleep and rDLPFC activity, specifically when performing the memory suppression task. “That’s interesting because many disorders associated with debilitating intrusive thoughts, such as depression and PTSD, are associated with disturbances in REM,” says Cairney.
“Intriguing” new research suggests a key role for REM sleep in maintaining proper memory control, says Zara Bergström, a cognitive psychologist at the University of Kent in England, who was not involved in the work. He added, however, that “future research will require direct manipulation of REM sleep” to confirm whether it has a causal role in memory and thought control.
Maria Wimber, a cognitive neuroscientist at the University of Glasgow, who was not involved in the research, added that the findings of the new study “have real potential to inform therapeutic approaches”.
“Interventions that improve REM sleep can be part of the therapy for disorders characterized by intrusive memories, such as post-traumatic stress disorder,” he says. This type of response can also be attempted for acute trauma, a possible preventative measure to ensure that toxic memories and flashbacks never surface.
