How Sleep Helps to Process Emotions

Summary: Study sheds light on how the brain processes emotions during dream sleep by consolidating positive emotions and dampening the consolidation of negative emotions. The findings could pave the way for new treatments for PTSD and other conditions related to negative emotional processing.

Source: University of Bern

Researchers from the Department of Neurology at the University of Bern and the University Hospital Bern have determined how the brain triages emotions during dream sleep to consolidate the storage of positive emotions and dampen the consolidation of negative emotions.

The work increases the importance of sleep in mental health and opens the way to new therapeutic strategies.

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

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

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

Processing emotions, especially distinguishing between danger and safety, is critical to the survival of animals.

In humans, excessive negative emotions, such as fear responses and anxiety states, lead to pathological states such as post-traumatic stress disorder (PTSD). In Europe, about 15% of the population is affected by persistent anxiety and severe mental illness.

The research group led by Antoine Adamantidis now provides insight into how the brain helps to amplify positive emotions and attenuate strongly negative or traumatic emotions during REM sleep.

This study is published in the journal Science

A double mechanism

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

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

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

“This means a disconnection of the two cellular compartments, in other words soma wide asleep and dendrites wide awake,” explains Adamantidis.

This decoupling is important because the strong activity of the dendrites allows the encoding of both danger and safety emotions, while the inhibitions of the soma completely block the output of the circuit during REM sleep. In other words, the brain favors the distinction between safety and danger in the dendrites, but blocks the overreaction to emotion, especially danger.

A survival advantage

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

“This bidirectional mechanism is essential to optimize the distinction between dangerous and safe signals,” said Mattia Aime of the DBMR, lead author of the study. If this distinction is missing in humans and excessive anxiety reactions are evoked, this can lead to anxiety disorders.

How and why these emotions are reactivated is unclear. Image is in the public domain

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

Breakthrough for sleep medication

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

Additional acute or chronic psychological problems that may imply this somatodendritic disconnection during sleep include acute and chronic stress, anxiety, depression, panic or even anhedonia, the inability to feel pleasure.

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

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

About this research news on sleep and emotional processing

Writer: press office
Source: University of Bern
Contact: Press Office – University of Bern
Image: The image is in the public domain

Original research: Closed access.
“Paradoxical somatodendritic uncoupling supports cortical plasticity during REM sleep” by Mattia Aime et al. Science


Abstract

Paradoxical 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 circuitry and synaptic mechanisms remain unclear.

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

This uncoupling reflects a shift of the inhibitory equilibrium between parvalbumin neuron-mediated somatic inhibition and vasoactive intestinal peptide-mediated dendritic disinhibition, mostly driven by neurons of the central medial thalamus.

REM-specific optogenetic suppression of dendritic activity led to a loss of danger-versus-safety discrimination during associative learning and a lack of synaptic plasticity, while optogenetic release of somatic inhibition resulted in enhanced 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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