Ikigai Daily
Menu
WonderFact

Sleep is more than rest: during the night the brain strengthens and sorts what it learned during the day and helps keep emotions in balance, while the body releases growth hormone and carries out repairs.

Ikigai Daily

ScienceHealthMind

The story behind the card

A night's sleep runs in cycles of about 90 minutes. Each cycle moves from light sleep into deep sleep and then into REM sleep, named after the rapid eye movements that come with it and the stage with the most vivid dreams. As early as 1924, the psychologists John Jenkins and Karl Dallenbach found that two volunteers remembered more of the nonsense syllables they had learned if they slept afterwards than if they stayed awake for the same time. In 2007, brain scans showed that after a night without sleep, the amygdala, an area involved in emotional reactions, responded far more strongly to upsetting pictures. In 2013, a study in mice found that the spaces between brain cells widen by about 60 per cent during sleep, helping fluid wash away waste. Regularly sleeping too little harms attention, learning and mood.

Türkçe oku
Uyku yalnızca dinlenmek değildir: Gece boyunca beyin, gün içinde öğrendiklerini pekiştirip düzene sokar ve duyguların dengede kalmasına yardım eder; beden de büyüme hormonu salgılar ve kendini onarır.

Bir gecelik uyku, yaklaşık 90 dakikalık döngülerden oluşur. Her döngüde hafif uykudan derin uykuya, oradan da REM uykusuna geçilir. REM adı, bu evreye eşlik eden hızlı göz hareketlerinden (İngilizce rapid eye movement) gelir; en canlı rüyalar da bu evrede görülür. Psikologlar John Jenkins ile Karl Dallenbach daha 1924'te iki gönüllüyle bir deney yaptı: Gönüllüler anlamsız heceler ezberledikten sonra uyuduklarında, aynı süreyi uyanık geçirdikleri zamana göre daha çok hece hatırladı. Amigdala, beynin duygusal tepkilerde rol oynayan bir bölgesidir; 2007'deki beyin taramaları, uykusuz geçen bir gecenin ardından amigdalanın üzücü görüntülere çok daha güçlü tepki verdiğini gösterdi. 2013'te farelerle yapılan bir çalışma, uyku sırasında beyin hücreleri arasındaki boşlukların yaklaşık yüzde 60 genişlediğini, bunun da sıvının atıkları temizlemesini kolaylaştırdığını ortaya koydu. Düzenli olarak az uyumak dikkati, öğrenmeyi ve ruh hâlini olumsuz etkiler.

Sources and further reading

Background reading: Sleep
Get the mobile appAbout our cards

Related cards

These cards share a subject or reading mode with the card above.

WonderScience

Deliberately smiling can make people feel slightly happier. In 2022 a study of nearly 4,000 people in 19 countries found that posing a smile, or copying a smiling face, raised reported happiness a little; a subtler method, holding a pen between the teeth, gave less clear results.

The idea that the face can feed back into feelings, called the facial feedback hypothesis, goes back to Charles Darwin and William James. In a famous 1988 experiment, Fritz Strack and colleagues had people hold a pen in their teeth, which forces a smile, or between their lips, which prevents one, and those in the first group rated cartoons as funnier. In 2016, seventeen laboratories repeated that experiment exactly and found no effect. A 2019 review of 138 studies concluded that the effect is real but small and varies from study to study. The 2022 Many Smiles Collaboration, led by Nicholas Coles and designed jointly by supporters and sceptics of the idea, found that deliberate smiling could both strengthen and start feelings of happiness, while the pen method remained inconclusive.

Ikigai DailyRead card
WonderScience

Your gut and brain communicate through nerves, hormones, immune signals and microbes, which is why stress and digestion can affect each other.

Scientists call this link the gut–brain axis. The gut has its own network of about 500 million nerve cells, the enteric nervous system, sometimes called the “second brain”, which can run digestion largely by itself. It is connected to the brain mainly through the vagus nerve, a long nerve running from the brainstem down to the abdomen, and most of its fibres carry messages upwards, from the gut to the brain. More than 90 per cent of the body's serotonin, a chemical messenger, is found in the gut. Gut bacteria play a part too: in a 2004 Japanese study, mice raised entirely free of germs overreacted to stress. Stress can speed up or slow down the gut, one reason it often worsens irritable bowel syndrome, a common gut disorder. Most research on the microbes' role has been in animals, and human evidence is still limited.

Ikigai DailyRead card
WonderScience

A placebo is a dummy treatment, such as a sugar pill. In pain studies, placebos can reduce the pain people report and also dampen activity in the brain areas that process pain, even though they contain no active drug.

The word placebo is Latin for “I shall please”. One of the first clues that the effect is physical came in 1978, when Jon Levine and colleagues studied patients recovering from wisdom tooth removal. They gave them a placebo and naloxone, a drug that blocks the effect of endorphins, the body's own painkilling chemicals. In patients who had responded to the placebo, naloxone increased the pain, which suggested that the placebo relief came from endorphins. In 2004 Tor Wager and colleagues used brain scans to show that a placebo painkiller reduced activity in pain-processing regions during a painful stimulus. Expectation works the other way too: in the nocebo effect, from the Latin for “I shall harm”, expecting harm makes symptoms worse. None of this means the pain was imaginary, or that placebos can replace effective treatment.

Ikigai DailyRead card
WonderScience

Emotions are not only feelings in the head. Fear speeds up the heart and breathing, grief can take away appetite and sleep, and joy changes posture and expression. These bodily changes are part of the emotion itself, and sensing them may be part of how we come to feel it.

In 1884 the American philosopher and psychologist William James turned the usual order around in an essay called “What Is an Emotion?”. We do not tremble because we are afraid, he argued; we feel afraid because we tremble. The physiologist Walter Cannon attacked the idea in 1927, and the debate ran for decades, but modern research keeps finding the body at the heart of emotion. In 2014 Lauri Nummenmaa and colleagues in Finland asked 701 people to colour in body outlines to show where they felt activity rise or fall with different emotions. Most emotions showed up in the chest, where breathing and heartbeat change; anger and happiness also lit up the arms, sadness appeared as weakened arms and legs, and disgust centred on the throat and stomach. The maps were similar for Finnish, Swedish and Taiwanese participants.

Ikigai DailyRead card
WonderScience

Scientists still have no single accepted explanation for why we dream. Dreams are most vivid in REM (rapid eye movement) sleep but also occur in other stages, and research links them with memory, emotion and the brain's own activity at night.

In 1953, Eugene Aserinsky and Nathaniel Kleitman at the University of Chicago noticed bursts of rapid eye movements (REM) during sleep and linked them to dreaming; people woken during REM sleep report a dream about 80 per cent of the time. Later studies found that people woken from other stages also report dreams, usually shorter and less story-like. Explanations differ. Sigmund Freud, in The Interpretation of Dreams (1899), saw dreams as disguised wishes. In 1977, Allan Hobson and Robert McCarley proposed that dreams are the brain's attempt to make a story out of random signals from the brainstem, the part of the brain that joins the spinal cord. Other researchers argue that dreams help us rehearse threats, sort memories or soften emotional experiences. Each theory explains some dreams, and none explains them all.

Ikigai DailyRead card
Next card in the archiveScientists still have no single accepted explanation for why we dream. Dreams are most vivid in REM (rapid eye movement) sleep but also occur in other stages, and research links them with memory, emotion and the brain's own activity at night.Read next →