SLEEP: How you manage emotions

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 remains a poorly understood process. The prefrontal cortex integrates most of these emotions during wakefulness but, paradoxically, appears at rest during REM sleep.

Better understand the processing of emotions during sleep.

From survival to mental illness: Lead author Prof. Antoine Adamantidis from the University of Bern and a physician at the Department of Neurology at the Inselspital (Bern University Hospital) recalls that the processing of emotions, in particular the ability to distinguish between danger and safety, is a essential function for survival. In humans, excessively negative emotions, such as fear and anxiety reactions, lead to pathological states such as post-traumatic stress disorder.

In Europe, 15% of the population suffers from anxiety and serious mental disorders.

The study: the researchers conditioned the mice to recognize auditory stimuli associated with safety and others associated with danger. The activity of neurons in the mouse brain was then recorded during the sleep-wake cycles. In this way, the researchers were able to map how emotional memories are transformed during REM sleep. Neurons are composed of a cell body (soma) that integrates information from dendrites (inputs) and sends signals to other neurons through its axons (outputs). The maps reveal that:

  • the cell bodies remain silent while the dendrites are activated: there is decoupling between the 2 cell compartments, that is, the cell body is deeply asleep and the dendrites are wide awake;

This decoupling allows:

  • dendrites, which are very active in encoding the emotions of danger and safety,
  • soma, inhibited, completely blocks signal output during REM sleep;
  • in other words, the brain favors safety over danger.

The coexistence of these 2 mechanisms is beneficial for stability and survival: “This bidirectional mechanism is essential to optimize the discrimination between dangerous signals and safety signals”says another lead author of the study, Mattia Aime.

When this mechanism malfunctions, excessive fear responses are generated, which can lead to anxiety disorders.

A “sleep medicine” to regulate emotions: These results open the way to a better understanding of the processing of emotions during sleep in humans and designate new therapeutic targets to treat traumatic memories, such as post-traumatic stress disorder (PTSD). Other acute or chronic mental health conditions that may involve this “somato-dendritic” uncoupling could also be involved, such as, acute and chronic stress, anxiety, depression, panic or even anhedonia or inability to feel pleasure.

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