Our brains are in the growth phase for the first two years of our life. But then a striking turnaround follows.
Sleep is very important to our health. Long-term lack of sleep can even lead to serious health problems. But why is sleep so essential to good health? In a new study , researchers have addressed this pressing question. And while sleep has many mysteries that have baffled scientists for decades, they have managed to formulate an answer.
From elephant to mouse
Scientists have been puzzling over a number of riddles for some time now. Why, for example, does a mouse sleep five times longer than an elephant? And why do babies sleep longer than adults? Apparently the smaller, the longer the sleep. And the bigger, the shorter the sleep. In the new study, the researchers attempted to explain this observation. And it turns out that the length of sleep is mainly related to the size of the brain.
In the study, the researchers conducted the most comprehensive analysis of sleep to date. They used aggregated data from more than 60 human and mammal sleep studies. They then studied data on sleep as we grow up – including total sleep time, REM sleep time, brain size, and body size – and built and tested a mathematical model to reveal how sleep changes with brain and body size.
The data was remarkably consistent. Because shortly after our second birthday – or its equivalent in other animal species – a striking change takes place. REM sleep in particular seems to suddenly decrease. “Before that age, the brain grows very quickly,” explains researcher Gina Poe. “During REM sleep, the phase in which we experience vivid dreams, the young brain is busy building and strengthening synapses, the connections between neurons.”
But the length of REM sleep does not appear to remain the same. The researchers discovered that REM sleep decreases as we age. For example, newborns spend about 50 percent of their sleep in REM sleep. By the age of 10 this has dropped to 25 percent and adults only spend 15 percent of the time in REM sleep. The significant decrease in REM sleep occurs around the second year of life, “as does the most significant change in sleep function,” said Poe.
S Monkey stages
Based on your brain activity, the activity ‘sleeping’ can be divided into different phases. You start with sleep phase 1. It only lasts for a short time: the frequency of the brain waves decreases and your breathing becomes slower. Then you move on to sleep phase 2: your muscles relax, and activity in the parts of the brain involved in thinking, reasoning, and problem solving decreases even further. This phase lasts about twenty minutes and is then exchanged for phase 3 and phase 4. Together these phases form ‘deep sleep’: your brain activity is minimal and you are almost impossible to wake up. This deep sleep lasts about half an hour. And then something crazy happens. Your brain and body quickly go through the different phases again until you get to phase 2 again. But instead of relaxing now your heart beats faster your breathing becomes shallow and your eyes dart back and forth. The REM phase has arrived. After your first dream, you go through the different phases again: NREM (the first four sleep phases) and then REM again, then NREM again and so on.
The researchers discovered that sleep has a completely different function for babies than it does for adults. After about two and a half years, the primary purpose of sleep changes. Brain growth is no longer the main goal, but maintenance and recovery, the researchers discovered. In other words, people sleep less in part because they no longer have to form as many new neural connections as when they are babies. Instead, sleep takes on a new important function. All animals naturally experience some degree of neurological damage during their awake hours. The resulting ‘waste’ – such as damaged genes and proteins in neurons – can build up and cause brain diseases. Sleep helps to repair this damage and clear up the debris. In fact, almost all of this brain repair takes place during our sleep.
The study shows how important a good night’s sleep is. “Sleep is just as important as food,” says Poe. “And it’s amazing how well sleep meets the needs of our nervous system. From jellyfish to birds and whales; everyone is asleep. But while we sleep, our brains don’t rest. ” Because as the findings show, our brains are busy clearing waste. A chronic lack of sleep, in which our brains are not given the opportunity to do this, can therefore have quite a few consequences. For example, it contributes to health problems such as dementia and other cognitive disorders, but also to diabetes and obesity.
Important to remember: 7.5 hours of sleep per night is normal for most adults. “When you start to get tired, don’t fight it, go to bed,” advises Poe. “A good night’s sleep is excellent medicine and it is free.” How you can best achieve a good night’s sleep? For example, sleep with your partner . Because as previous research has shown, sleeping together improves your REM sleep, among other things. And that also boosts your mental health, memory and problem solving skills.