Chinstrap penguins can fall asleep more than 10,000 times a day but deep sleep only lasts an average of four seconds, according to research indicating that episodes of microsleep can have a restorative effect on these birds and possibly other species as well. Although the results cannot be extrapolated to the human species, they call into question the current theory that fragmented sleep cannot be restorative.
The research was carried out during the breeding season in a penguin colony on King George Island, Antarctica. As is common among penguins, the male and female take turns incubating the eggs, so one stays in the colony and the other goes to feed at sea. Shifts last an average of 22 hours, although there have been cases of stragglers taking more than 60 hours to return.
For the consort who is left in charge of the eggs, falling asleep would be a danger because on King George Island there are predatory birds – the Stercorarius antarcticus, or Antarctic robbers – that steal eggs. Additionally, prospective parents must defend their nest from other penguins in the colony.
This could explain why chinstrap penguins have developed a form of sleep that allows them to sleep while remaining alert, say the authors of the research, co-led by the Neuroscience Research Center of Lyon (France) and the Polar Research Institute of Korea.
According to results presented today in the journal Science, chinstrap penguins (Pygoscelis antarcticus) very quickly reach a state of deep sleep, which is characterized by slow brain waves. These animals, about 70 centimeters tall, which are identified by a thin black line on the underside of their heads, usually fall asleep almost ten times a minute, both standing and lying down, and accumulate twelve hours of deep sleep a day. .
Researchers have studied 14 penguins to which they placed sensors to measure their brain activity, body movements and location, in addition to monitoring them by video.
“Their ability to successfully reproduce, despite sleeping in this highly fragmented manner, suggests that microsleeps can fulfill at least some of the restorative functions of sleep,” the authors of the paper conclude in Science.
These results “challenge the current interpretation that fragmentation is inherently detrimental to sleep quality,” add in an analysis article Christian Harding and Vladyslav Vyazovskiy, from the universities of California at San Diego and Oxford, respectively, who have not participated in the research.
“It is research that makes us question our ideas about the architecture of sleep, but the results in penguins cannot be extrapolated to people because sleep is very variable depending on the species,” warns Raquel López, a specialist in sleep medicine at the AdSalutem institute in Barcelona.
In the human species, there is no evidence that the brain directly enters a state of deep sleep except in exceptional situations of sleep deprivation. Furthermore, “in mammals there is a minimum duration of sleep below which it is no longer restorative,” says neuroscientist Luis de Lecea, a specialist in sleep biology at Stanford University (USA). According to research led by De Lecea and carried out on mice, when sleep lasts less than 60 seconds it loses its memory consolidation function.
On the contrary, it has been observed that short naps have a beneficial effect by improving the ability to pay attention and concentrate in the following hours. “This beneficial effect occurs without the need to enter deep sleep, which usually occurs approximately thirty minutes after the onset of sleep,” says Raquel López. “It is recommended that naps be less than half an hour so as not to go into deep sleep and avoid finding yourself in a state of disorientation when you wake up.”
For naps to be beneficial, De Lecea warns, they should be done at times when they do not interfere with the need to sleep at night.
According to the authors of the research carried out on penguins, their results “suggest that the benefits of sleep can accumulate progressively” throughout the day.
