July 29, 2015 : Amazing Ways of Sleeping
© 安岡喜晴 (JoyShine)
Today I visited the Osaka Prefectural Government.
There I was asked, "Is five hours of sleep a day enough?"
In a joint consensus statement released this year, the American Academy of Sleep Medicine and the Sleep Research Society recommend that adults should sleep at least seven hours a night on a regular basis to stay healthy.
The amount of sleep a person needs varies, but for most people, five hours a night every day is not enough.
The effects of sleep loss are not completely reset each night.
Studies have reported that when people keep their sleep to six hours or less a day, declines in attention, reaction speed, and similar functions accumulate day by day.
The troubling part is that we cannot always see that decline in ourselves accurately.
Even when we feel we have gotten used to short sleep, we may actually be overlooking more and reacting more slowly.
The brain does not necessarily sleep as a whole, all at once.
A study in rats published in 2011 showed that after long periods of wakefulness, some neurons in the cerebral cortex temporarily pause their activity, as they do during sleep, even though the animal itself stays active.
When this "local sleep" occurred, the rats also made more mistakes in what they were doing.
This is not a convenient ability that lets an animal stay active while resting the brain efficiently.
At least in this experiment, part of the brain simply became unable to keep itself awake after being awake for too long.
On the other hand, some animals sleep in a more ingenious way, as an adaptation for staying alive.
Some marine mammals such as dolphins, and some birds, have what is called "unihemispheric sleep," in which one cerebral hemisphere sleeps while the other stays awake.
It is thought to help marine mammals surface to breathe, and to help birds keep one eye open against predators.
That does not mean that fish swim and birds fly without any sleep at all.
Fish also have a state equivalent to sleep.
In zebrafish, not only do they become still for a while, but their reactions to outside stimuli also weaken, and when that state is disrupted, more sleep follows.
It has also been debated for some time whether migratory birds sleep during long flights, but sleeping with half the brain is one thing, and flying safely for days without any sleep is another.
Humans, meanwhile, do not have the ability that dolphins and some birds have, which is to keep working while one side of the brain sleeps safely.
Even when we do not get enough sleep, the human brain cannot go half asleep like that.
The only thing that happens is that part of it stops working, and the person does not notice.
This state is especially dangerous for medical workers and drivers.
A brief drop in attention can lead to a wrong drug, a missed change in a patient's condition, or a traffic accident, and any of these can be serious.
Sleeping longer on the weekend does bring some recovery from sleep loss.
Even so, functions that have declined over several days of short sleep do not always come all the way back after one long night.
In a study that restricted sleep to four hours a night for five nights, part of the decline remained even with ten hours of recovery sleep.
So instead of thinking, "Five hours on weekdays is fine with eight hours on the weekend," it is important to secure enough sleep from day to day.
Animals have developed a surprising variety of ways of sleeping in order to survive in their own environments.
But humans are neither birds nor dolphins.
To keep the brain working properly and to work safely, we should not keep going while part of the brain is quietly failing.
We need to sleep well every day and rest the whole brain.
