Scientists have figured out how pupils behave during sleep

© RIA Novosti / Natalia to Seliverstova in photobacteria page of social network Facebook in the eyeScientists have figured out how pupils behave during sleep© RIA Novosti / Natalia to Seliverstova the image Bank

Scientists tracked the eye movement and the size of the pupils from the sleeping mice and found that they narrowed during deep sleep and are expanding at a time when rodents have dreams, says the article, published in the journal Current Biology.

«We found that pupils rhythmic way narrowed and expanded during sleep. Interestingly, these changes in the sizes almost perfectly match with the changing level of brain activity, which suggests that the size of the pupils reflect the current phase of sleep – the smaller they are, the deeper the sleep,» says Daniel Huber (Daniel Huber) from the University of Geneva (Switzerland).

There are two types of sleep — rapid and slow sleep, which constantly alternate with each other. When falling asleep, there comes a phase of slow sleep, during which the body gradually «turned off» and regain strength.

During REM sleep the body switches to «work mode», but all muscles «shut down» for the sake of security, and the person becomes totally immobile. This phase is characterized by rapid chaotic eye movements, it is believed that at this time people see the most vivid dreams.

Until recently, as noted by Huber, scientists believed that dreams, the consolidation of information and other «difficult» elements of the dream are a unique feature of humans and other primates that are inaccessible to mammals with a more primitive brain, as well as birds and reptiles. Oversee the work of the brain of rats and birds suggest that it is most likely not.

Huber and his team found new evidence in favor of this idea, for the first time tracked how change the size and position of the pupil of the mice during sleep. To do this, scientists have created a special «harness» for rodents, which kept their body and head in one position during sleep, which allowed them to watch their eyes using an infrared camera.

The pupil, as the scientists explain, lets in more heat than the iris of the eye and other regions, making it possible to see even if the eyes of a human or animal is closed, if it is illuminated from the side using an infrared «flashlight» or led.

As shown by such observations, the eyes of the mice behave in an unusual way during sleep, changing the size of the pupils in the transition from fast to slow sleep and Vice versa, obeying the signals of the vegetative nervous system.

Constriction of the pupil during the phase of slow sleep, as scientists assume, due to one simple thing – during this phase of sleep is the consolidation of memories and their transfer into long-term memory, and signals from the outside world, including the light coming into the eye through the eyelids, can interfere with this process.

«The popular notion that the eyes are the «gates of the soul» can even be true during sleep when our eyelids are closed. Pupils continue to play an important role in the nervous system during sleep, blocking external signals and protecting the brain from the «noise» during memory consolidation,» concludes Özge USEC (Ozge Yuzgec), a colleague of Huber.