July 5, 2022 – REM sleep is the darling of the sleep world. Short for “rapid eye movement,” REM fascinates us because it’s when we do most of our dreaming – when, supposedly, all of our inner fears, frustrations, and passions play out.
We already have compelling evidence that REM sleep helps us process those emotions, but a new study reveals how.
Turns out, neurons (messenger cells) in the front of the brain may be busy reinforcing positive emotions while also dampening our most negative and traumatic ones, say researchers from the University of Bern, and University Hospital Bern, in Switzerland. It’s a protective mechanism, they believe.
The findings not only reinforce the importance of sleep for mental health but may also lead to new therapies for some mental health conditions.
How Sleep Helps Us Process Emotion
The researchers came to their conclusions after studying brain activity in mice during wakefulness, REM, and non-REM sleep.
They wanted to find out why the front of the brain – the prefrontal cortex – is actively integrating many emotions when you’re awake but appears inactive during REM sleep, says lead study author Mattia Aime, a post-doctoral researcher in the Department of Biomedical Research at the University of Bern. It’s a baffling phenomenon, the authors note in their study in the journal Science.
Neurons have three key parts, Aime explains – dendrites, axons, and the cell body (soma). Dendrites receive information and send it to the cell body. Then the information is transferred to axons that help send it to other neurons. So, dendrites pull information in, and axons send it out.
But the researchers discovered that during REM, emotional content was stored at the dendritic level, and the “output” part of the cell stopped communicating.
“This means that the dendrites, active during REM sleep, provided a substrate for consolidation,” Aime says, blocking any outgoing messages related to danger. Think of it as a game of “whisper down the lane” that stops short when someone receives a scary or negative whisper and doesn’t pass it on to the next person.
Aime calls the mechanism “bi-directional” because different parts of the neuron (the “input” and “output” parts) behave in opposite ways.
“This is essential to optimize the consolidation of emotional memories,” Aime says. “Dendrites store information, cell bodies [become] inactive to avoid over-storage.”
Advancing Sleep Medicine
The findings may help with treatment of sleep-related mental health conditions, such as posttraumatic stress disorder (PTSD), which can cause nightmares.
“The interaction of REM-dependent learning and PTSD is of great interest,” Aime says, noting that when this process is compromised, it can lead to PTSD-like behavior.
REM sleep is also believed to play a role in anxiety and major depressive disorder.
“These findings pave the way to a better understanding of the processing of emotions during sleep in the mammalian brain and open new perspectives for new therapeutic targets,” he says.
