Science: Breakthrough in sleep medicine: The brain consolidates positive emotions in dreams

Processing emotions, especially distinguishing danger from safety, is essential for animal survival. In humans, excessive negative emotions, such as fear responses and anxiety states, can lead to pathological conditions such as post-traumatic stress disorder (PTSD).

In Europe, approximately 15% of the population is affected by persistent anxiety and serious mental illness.

Now, a research team led by Professor Antoine Adamantidis of the Department of Neurology at the University of Bern and the University Hospital of Bern has provided insights into how the brain helps strengthen positive emotions and weaken strong negative or traumatic emotions during dream sleep.

In the study, scientists found that the brain categorizes emotions during dream sleep and consolidates the storage of positive emotions while suppressing negative ones. The researchers said the work highlights the importance of sleep in mental health and could open up new treatment strategies.

The relevant research results were published in the recent issue of Science magazine.

The prefrontal cortex integrates many of these emotions during wakefulness, but suddenly becomes silent during REM sleep. "Our goal was to understand the underlying mechanisms and functions of this surprising phenomenon," says Professor Antoine Adamantidis of the Department of Neurology at the University Hospital of Bern.

Breakthrough in sleep medicine

Rapid eye movement (REM) sleep is a unique and mysterious sleep state in which the majority of dreams occur with intense emotional content. How and why these emotions are reactivated is unclear.

To investigate this question, the researchers first asked mice to recognize auditory stimuli associated with safety and other auditory stimuli associated with danger (aversive stimuli), and then recorded the activity of neurons in the mice's brains during their sleep-wake cycle.

Figure | Scientists use optogenetics to study neuronal activity (Source: University of Bern)

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

The cell body of a neuron is able to integrate information from its dendrites (input) and send signals to other neurons through its axon (output). But the results showed that while their dendrites were activated, the cell body remained silent.

"This means a decoupling of the two cell compartments, in other words, the cell body is completely asleep and the dendrites are completely awake," Adamantidis explains. This decoupling is important because the intense activity of the dendrites allows encoding of emotions of danger and safety, while during REM sleep, the inhibition of the cell body completely blocks the output of signals.

In other words, the brain tends to distinguish safety from danger in its dendrites, but prevents overreaction to emotions, especially to danger.

The researchers believe that the coexistence of these two mechanisms is beneficial to the stability and survival of the organism. If humans lack this distinction and develop an excessive fear response, this could lead to anxiety disorders. These findings are particularly relevant to pathological conditions such as post-traumatic stress disorder, in which traumatic memories are overconsolidated in the prefrontal cortex day after day during sleep.

Furthermore, these findings pave the way for a better understanding of emotional processing during human sleep and open up new perspectives for treating traumatic memories, such as post-traumatic stress disorder (PTSD). Other acute or chronic mental health problems that may be associated with this somatodendritic uncoupling during sleep include acute and chronic stress, anxiety, depression, panic, and even anhedonia, the inability to feel pleasure.

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

The Importance of Sleep

Nowadays, insomnia has become an important problem affecting the health of modern people. More than 300 million people in my country have sleep disorders, and the incidence of insomnia in adults is close to 40%. The quality of sleep not only affects people's emotions, but also their immune system. Moreover, insomnia is often one of the external manifestations of a potential disease in the body.

Why is sleep so important? According to previous research by Professor Yu Hayashi's research team at the International Institute of Integrated Sleep Medicine at the University of Tsukuba in Japan, the blood flow rate in the brain of mammals increases significantly during rapid eye movement sleep, which is essential for the removal of accumulated waste from the brain.

We all know that sleep is essential for health. If we don’t sleep well for a few nights, we will feel irritable, have low learning efficiency, and lose appetite. After all, people spend one-third of their lives sleeping, and lack of sleep can lead to a series of problems such as obesity, cardiovascular and cerebrovascular diseases, depression, and so on.

(Source: pixabay)

Human sleep is affected by biological rhythms, and each sleep cycle has its own sleep cycle and sleep stage. The human sleep cycle includes two phases: non-rapid eye movement sleep (NREM) and rapid eye movement sleep (REM). NREM and REM alternate, and each alternation is called a sleep cycle. The two cycles go back and forth, and there are usually 4 to 5 sleep cycles per night, each cycle lasting 90 to 110 minutes. As the sleep cycle continues, the proportion of REM sleep gradually increases.

At present, a large number of studies have shown that NREM sleep and REM sleep are both important for humans. Among them, REM sleep is crucial for human memory consolidation and synaptic plasticity, while NREM sleep is closely related to human growth hormone secretion, immune activation, inflammation and other functions.

During REM sleep, although the body is paralyzed, the brain behaves in some ways like it is awake, with rapid eye movement and relaxed body muscles. Most vivid dreams that are recalled upon waking occur during REM sleep.

At the same time, during REM sleep, the blood flow to the brain increases significantly, a process that is essential for clearing the various metabolic wastes produced by the normal activity of neurons. Sleep disorders can lead to a disorder in this process and are closely related to neurodegenerative diseases such as Alzheimer's disease.

This means that not only is sleep important, but high-quality sleep with dreams is also more important.

References:

https://www.science.org/doi/10.1126/science.abk2734

https://www.unibe.ch/news/media_news/media_relations_e/media_releases/2022/media_releases_2022/how_sleep_helps_to_process_emotions/index_eng.html

https://www.cell.com/cell-reports/fulltext/S2211-1247(21)00992-X