The trick to being able to sleep with one eye open

There are people who, when they wake up, aren't human until they've had at least a couple of cups of coffee. Others, on the other hand, wake up in a good mood and with their brains already working at cruising speed as soon as they put on their sneakers. Technically—and with a touch of humor—the former have been labeled as night owls already the seconds how a morning larks, in honor of night owls and early morning larks, respectively. As much as it annoys us, neither of them is to blame for preferring a specific distribution of their daily activity/sleep pattern, what is called chronotype: belonging to one group or another basically depends on the genes passed on to you by your parents.

But in some animals, like birds themselves, this division between sleeping and being awake isn't actually defined so radically, because they have an advantage over us: they're capable of sleeping asymmetrically. This means that while one side of the brain weighs figs, the other is fully alert, which is what popular culture has graphically described as sleeping with one eye open.

Surely many humans would like to be able to progress through sleep while engaged in activities that don't require full attention, but unfortunately, evolution hasn't needed to endow us with this superpower, which is especially useful for animals that must constantly be on the lookout for the next predator, even when resting. Birds can even fly in asymmetrical sleep, which, for example, allows them to be alert enough to avoid colliding with other birds traveling through the same airspace. Some mammals benefit from similar advantages, such as seals, which can swim with one hemisphere of their brain asleep, or reindeer, which have numerous episodes of "microsonics" throughout the day, a kind of nap that lasts seconds and during which they can even continue thinking.

The human night watch

Despite our inability to sleep halfway, humans are also capable of not completely shutting off when we go to bed. It's been shown that the first time we spend the night in a new place, our sleep will be less deep, at least in the left hemisphere, allowing us to be more alert to sounds that might herald unexpected danger. The effect disappears the following night, when we're more familiar with our surroundings. This would be similar to what happens when ducks sleep in a tight spot: those in the middle of the group can relax enough to fall into a completely symmetrical sleep, while those on the periphery must keep one eye open to watch out for possible scares.

This human "night watch," somewhat reminiscent of asymmetrical sleep, suggests that, with a little training, we might be able to shut off one hemisphere and not the other. But we must keep in mind why we need to sleep. The consensus is that essential maintenance and housekeeping tasks are performed in the brain during sleep. Since ours is particularly hyper-revved compared to other animals, it's quite possible that a partial blackout won't be enough for them and they'll need a full night's sleep at once to recover from daytime activity.

In fact, something similar happens to animals that are fortunate enough to be able to sleep asymmetrically, because it has been observed that all those who do so, at one time or another, must also resort to normal sleep. Why, if sleeping in stages clearly has more advantages? A recently published article in the journal Current Biology The study, by Dr. Peter Meerlo's group at the University of Groningen, attempts to answer the question by proposing that this partial sleep is only possible in the absence of pressures forcing a more complete recovery. To demonstrate this, the researchers measured the brain electrical activity of jackdaws that slept as much as they wanted and other jackdaws that rested after being kept awake for a few hours. They observed that asymmetrical sleep was more frequent as the night progressed and was hardly seen when the birds had not been allowed to sleep when they wanted. This would indicate that partial disconnection could only occur when the brain is sufficiently rested. If not, the birds must do their part and sleep soundly for the hours they are supposed to. In other words, even animals that are lucky enough to be able to switch off areas of the brain in turns must yield to "classical" sleep when they need a rest. reset deep and rest completely.

Sleep is still a largely unknown, but studying animal behavior can provide clues as to why we should sleep and how to optimize the hours we disconnect our neurons. In recent years, it has been discovered that a lack of sleep can have significant effects on health, both physical and mental, and even influence the aging of organs like the brain itself. It's clear that Morpheus can't be denied hours, because the price we pay can end up being steep. And not even the birds escape this.