Poor sleep related with inability to keep unwanted memories at bay, study finds

NEW DELHI: How poor sleep affects mental health could be related to a low function of brain regions that work to keep unwanted,

intrusive memories

at bay, according to a new study. Intrusive thoughts and memories, while occasional and momentary for most, can be recurrent, vivid and upsetting for those suffering from mental disorders, such as depression, anxiety and post-traumatic stress disorder, Marcus Harrington, a lecturer of psychology at the University of East Anglia, UK, and lead author of the study published in the journal Proceedings of the National Academy of Sciences, explained.
Researchers compared brain scans of participants who slept and did not sleep the previous night, and found ‘memory control’ problems in the sleep-deprived — they faced difficulties in engaging brain regions that suppress the process of retrieving memories.
“Memories of unpleasant experiences can intrude into conscious awareness, often in response to reminders,” Harrington said.
“Given that memories play a central role in our affective perception of the external world, memory control failures may go a long way towards explaining the relationship between sleep loss and emotional dysregulation,” the lead author said.

REM, or rapid eye movement, sleep — the stage when one dreams — was found to help restore function in the brain regions involved in memory control. In a healthy adult, the REM stage accounts for about a quarter of a whole night’s sleep.
“Taken together, our findings highlight the critical role of sleep in maintaining control over both our memories and ongoing thoughts,” Harrington said.
The study could also help develop treatments and prevention strategies for mental illnesses, such as depression and anxiety, the researchers said.

For the study, functional MRI brain scans of 85 healthy adults were taken while attempting to suppress unwanted memories — half the participants had a rested sleep in the lab, while the other half was awake all night.
Among the well-rested, suppressing memory was related to a heightened activity in the right dorsolateral prefrontal cortex — a brain region that controls thoughts, actions, and emotions — along with a reduced activity in the hippocampus, known to help in retrieving memories.
Further, those spending more time in REM sleep were found to be better at engaging the right dorsolateral prefrontal cortex during memory suppression.
The researchers said this pointed to how the ‘dreaming’ stage of sleep could help restore brain processes that prevent unwanted memories from entering conscious thought.
“We show that sleep deprivation disrupts prefrontal inhibition of memory retrieval and that the overnight restoration of this inhibitory mechanism is associated with time spent in rapid eye movement (REM) sleep,” the authors wrote.