How Missing Sleep Lets Bad Memories Haunt Your Mind

Research reveals that a lack of sleep can hinder the brain's ability to suppress unwanted memories and intrusive thoughts, emphasizing the importance of restful sleep for mental health.

Sleep deprivation has been found to hinder the brain's ability to suppress unwanted memories and intrusive thoughts, according to a new study.

Researchers from the University of York, working with the University of East Anglia, discovered that sleep deprivation disrupts the prefrontal brain's capacity to block the retrieval of memories that would typically be suppressed.

Dr. Scott Cairney, from the University of York, explained: "Memories of unpleasant experiences often intrude into our conscious mind in response to reminders, but tend to be fleeting and can be put out of the mind again, but we have previously shown that the brain's ability to suppress such intrusive memories is contingent on obtaining restful sleep.

"Suppression is a very clever function of the brain as it weakens all of the connecting traces of the memory, thereby inhibiting us from joining up all the dots to retrieve the full picture of the experience when it is triggered by an external stimulus."

Experimental Insights

To understand how the brain does this, the team used functional magnetic resonance imaging (fMRI) scans to investigate the brain activity of 85 healthy adults, half of which had experienced a healthy night sleep in the sleep lab, and the other half stayed awake all night.

They were asked to look at faces, which they had previously seen paired with images of scenes, some of which were emotionally negative, such as a picture of a car crash or a fight. For each face, they were asked to either recall the scene associated with it, or suppress the memory of the scene.

When attempting to suppress the scene images, the well-rested participants showed more activation in the right dorsolateral prefrontal cortex — a brain region that controls thoughts, actions, and emotions — compared to those who stayed awake all night.

REM Sleep and Memory Management

The rested participants also showed reduced activity in the hippocampus — a brain region involved in memory retrieval — during attempts to suppress unwanted memories, demonstrating that they could 'shut down' the retrieval operations that underpin emerging intrusive thoughts.

They also found that individuals who obtained more rapid eye movement (REM) sleep, were better able to engage the right dorsolateral prefrontal cortex during memory suppression, pointing to a role for REM sleep in restoring the mechanisms in the brain that can help prevent unwanted memories from entering conscious thought.

Dr. Cairney explains: "The participants who were sleep deprived were unable to engage the area of the brain that helps us suppress unwanted memories. Consequently, they could not quash memory-related processes in the hippocampus that give rise to intrusive thoughts.

"This is really important to our understanding of mental health issues as it is well documented that those who suffer with anxiety, depression or PTSD, also have difficulty with sleep. Now that we have better understanding of the the mechanisms in the brain that can help restrict negative memories and thoughts, we can perhaps work on more targeted treatments and behavioral therapies that help with improving sleep and as a result support the brain in doing what it has so cleverly adapted to doing, allowing us to lead mentally fit lives."

Reference: "Memory control deficits in the sleep-deprived human brain" by Marcus O. Harrington, Theodoros Karapanagiotidis, Lauryn Phillips, Jonathan Smallwood, Michael C. Anderson and Scott A. Cairney, 31 December 2024, Proceedings of the National Academy of Sciences.
DOI: 10.1073/pnas.2400743122