How Sleep Helps Process Emotions

How Sleep Helps Process Emotions

Summary: A study sheds light on how the brain processes emotions during dream sleep by consolidating positive emotions while dampening the consolidation of negative emotions. The findings could pave the way for new treatments for PTSD and other disorders associated with negative emotional processing.

Source: University of Bern

Researchers from the Department of Neurology at the University of Bern and the University Hospital of Bern have identified how the brain sorts emotions during dream sleep to consolidate the storage of positive emotions while attenuating the consolidation of negative emotions.

The work expands the importance of sleep in mental health and paves the way for new therapeutic strategies.

Rapid eye movement (REM or REM) sleep is a unique and mysterious sleep state in which most dreams occur with intense emotional content.

How and why these emotions are reactivated is unclear. The prefrontal cortex integrates many of these emotions during wakefulness but paradoxically appears at rest during REM sleep.

“Our goal was to understand the underlying mechanism and functions of such a surprising phenomenon,” says Professor Antoine Adamantidis from the Department of Biomedical Research (DBMR) at the University of Bern and the Department of Neurology at the Inselspital , Bern University Hospital.

The processing of emotions, in particular the distinction between danger and safety, is essential to the survival of animals.

In humans, excessively negative emotions, such as fear reactions and states of anxiety, lead to disease states such as post-traumatic stress disorder (PTSD). In Europe, about 15% of the population suffers from persistent anxiety and serious mental disorders.

The research group led by Antoine Adamantidis is now shedding light on how the brain contributes to reinforcing positive emotions and weakening strongly negative or traumatic emotions during REM sleep.

This study was published in the journal Science.

A dual mechanism

The researchers first conditioned mice to recognize auditory stimuli associated with safety and others associated with danger (aversive stimuli). The activity of neurons in the mouse brain was then recorded during sleep-wake cycles.

In this way, the researchers were able to map different areas of a cell and determine how emotional memories are processed during REM sleep.

Neurons are composed of a cell body (soma) which integrates information from dendrites (inputs) and sends signals to other neurons via their axons (outputs). The results obtained showed that the cell somas are kept silent while their dendrites are activated.

“This means a decoupling of the two cellular compartments, i.e. sleeping soma and awake dendrites,” says Adamantidis.

This decoupling is important because the high activity of dendrites allows the encoding of both danger and safety emotions, while soma inhibitions completely block circuit output during REM sleep. In other words, the brain promotes discrimination of safety versus danger in the dendrites, but blocks over-reaction to emotion, especially danger.

A survival advantage

According to the researchers, the coexistence of the two mechanisms is beneficial to the stability and survival of organisms:

“This bi-directional mechanism is essential to optimize the discrimination between dangerous and safe signals”, explains Mattia Aime of DBMR, first author of the study. If this discrimination is lacking in humans and excessive fear reactions are generated, this can lead to anxiety disorders.

It shows a sleeping person
How and why these emotions are reactivated is unclear. Image is in public domain

The results are particularly relevant for pathological conditions such as post-traumatic stress disorder, in which trauma is overconsolidated in the prefrontal cortex day after day during sleep.

Breakthrough for sleep medicine

These findings pave the way for a better understanding of sleep-emotional processing in humans and open new perspectives for therapeutic targets to address the maladaptive processing of traumatic memories, such as post-traumatic stress disorder (PTSD) and their early sleep-dependent consolidation. .

Other acute or chronic mental health conditions that may involve this somatodendritic uncoupling during sleep include acute and chronic stress, anxiety, depression, panic, or even anhedonia, the inability to experience pleasure.

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Sleep research and sleep medicine have long been a focus of research at the University of Bern and the Inselspital, University Hospital of Bern.

“We hope that our findings will be of interest not only to patients, but also to the general public,” says Adamantidis.

About this sleep research and emotional processing news

Author: Press office
Source: University of Bern
Contact: Press service – University of Bern
Picture: Image is in public domain

Original research: Access closed.
“REM Somatodendritic Uncoupling Supports Cortical Plasticity During REM Sleep” by Mattia Aime et al. Science


Abstract

REM somatodendritic uncoupling supports cortical plasticity during REM sleep

Rapid eye movement (REM) sleep is associated with the consolidation of emotional memories. Yet the underlying neocortical circuits and synaptic mechanisms remain unclear.

We found that REM sleep is associated with somatodendritic uncoupling in pyramidal neurons in the prefrontal cortex.

This uncoupling reflects a shift in inhibitory balance between somatic inhibition mediated by parvalbumin neurons and dendritic disinhibition mediated by vasoactive gut peptides, primarily driven by neurons in the central medial thalamus.

REM-specific optogenetic suppression of dendritic activity resulted in loss of discrimination between danger and safety during associative learning and lack of synaptic plasticity, while optogenetic release of somatic inhibition resulted in increased discrimination and synaptic potentiation.

Somatodendritic uncoupling during REM sleep promotes opposing synaptic plasticity mechanisms that optimize emotional responses to future behavioral stressors.

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