When her daughter is in preschool, Rebecca Spencer experiences something that many parents and caregivers know: the power of napping.
Without a nap, his daughter is dizzy, irritable, or both at the same time.
Spencer, a sleep specialist neurologist at the University of Massachusetts Amherst, in the United States, wants to investigate what lies behind this anecdotal experience.
"Many people realize that a child without sleep is emotionally regulated," he explained. "That makes us ask ourselves, & # 39; Does napping really help process emotions? & # 39;"
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Scientific research has shown that, in general, sleep helps us to understand emotions. In fact, it plays a key role in the coding of information taken from that day's experience, so it's important to keep memories.
And emotional memories are unique because of the way they activate the body of the amygdala: the emotional core of the brain.
"Activating the body of the amygdala is what allows you to remember your wedding day and the funeral of your parents more than any other working day," Spencer said.
The amygdala body labels this memory as meaningful, so that during sleep they are processed longer and are repeated more than other trivial memories.
The result is that emotionally important memories are more easily restored in the future.
But by having an influence on how memory is processed, the dream can also change the strength they have.
"Sleep is very effective when it comes to changing emotional memory," said Elaina Bolinger, an emotion and sleep specialist at Tuebingen University, Germany.
In a recent study, Bolinger and his colleagues showed negative and neutral images for children between 8 and 11 years. Children show their emotional response by choosing simple people's pictures.
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Then, some children sleep and others don't. The researchers controlled the physiology of their brains through electrodes from the next room.
The next morning, the children saw the same picture, as well as several new photos. And compared to children who stay awake, children who sleep better control their emotional responses.
This research shows that sleep helps crystallize emotional information and controls how it makes us feel. And this effect happens quickly.
"A lot of research now shows that one night of sleep is beneficial," Bolinger said. "This is useful for processing memory, and it's also important for regulating emotions in general."
But not all dreams are the same.
Type of sleep
Rapid eye movement (REM) sleep is associated with emotional memory, and REM sleep which causes more people to evaluate other people's intentions and remember emotional stories.
One theory shows the absence of the noradrenaline stress hormone during REM sleep. Temporarily released from this hormone, the brain can process memory without stress.
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Simon Durrant, head of the Laboratory of Sleep and Cognition at the University of Lincoln, in England, highlighted another aspect.
The prefrontal cortex is the most developed part of the brain: this is where Durrant says, "the human urge to stay calm and not react immediately to things."
During waking up, this is the part that keeps the body of the amygdala under control and, therefore, emotions. During sleep, the connection decreases.
"In a certain sense, as long as REM sleep is emotionally rampant."
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But Spencer believes that non-REM sleep also plays an important role. Slow wave sleep (SWS) is the first sleep phase that combines memory, and is very effective when processing neutral memory.
Spencer's research shows that the amount of SWS activity during sleep affects the way emotional memory is changed.
Napping consists mainly of non-REM sleep. And the latest article written by Spencer seems to be the first to show that napping, and not just sleeping at night, contributes to the processing of emotional memory in children.
Without napping, children show bias towards emotionality. By taking a nap, they respond similarly to neutral stimuli and emotional stimuli.
In short, he assured that "if they do not take a nap, children become very sensitive to emotional stimulation," because they do not consolidate the emotional burden on that day.
Spencer believes that napping also contributes to emotional processing in adults, although not at the same level. An adult has a more mature hippocampus and, therefore, more ability to preserve memories. Not sleeping doesn't hurt them too much.
However, that is only to a certain extent. Spencer's research related to aging shows that "we need to consolidate memory more often as we get older."
Interestingly, older adults show a bias towards positive memories, while young adults tend to be negative.
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This may be because children and adolescents focus on negative experiences because they contain key information that must be learned: from the danger of fire to the risk of receiving drinks from strangers.
But towards the end of life, people prioritize the positive. They also have less REM sleep, a type of sleep that is likely to store negative memories, especially in people with depression.
The sleep researcher also analyzes the potential of certain aspects of sleep to treat post-traumatic stress disorder (PTSD).
One study showed that sleeping 24 hours from a traumatic experience made the memories not too sad later on. For sufferers of anxiety, sleep therapy can help them remember that they eliminate their fears.
Conversely, wakefulness therapy – where people are deliberately deprived of sleep – spreads as a method to treat depression.
Insomnia can in some cases have a protective effect. Spencer noted that, after trauma, "the natural biological response to the condition is to have insomnia."
Thus, it can sometimes be good that lack of REM sleep damages the brain's ability to consolidate emotional memory.
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"There is evidence that people with longer REM sleep tend to be more depressed," Durrant said. Experts believe that this is because some people with depression consolidate negative memories during REM sleep.
"I don't think I will be able to see this problem resolved," he said of all the potential clinical applications of sleep and wakefulness therapy.
But what is clear is that certain types of decision making improve after sleep, in part because the sleep method regulates all those rounds of feeling.
Bolinger explains it clearly: in general, "sleep helps you feel better".
In the end, the best recipe for a broken heart or a cloudy mind might be a nap.
Read original stories in English on BBC Future.