Detects the second light sensing system in the human eye

New research for blind people provides a proof for the human eye hypothesis that there are two separate light-sensing systems: a conventional visual signal reception helps us to see and a specific system. Other differences help us recognize day and night.

It has long been known that eyes must perform both functions but only in recent years have we come to think that both eyesight and control of the rhythm of sleep reminds us when to go to bed and when we need it. apple. Both functions are performed at the same time thanks to rods and cones located on the retina. These are also cells that help us see things.

Research on healthy humans and animals made in the 1990s has shown: Although rod and cone cells control vision, but the signals that synchronize our body clock with the time of sunrise and sunset is because the cells sensitive to light lie at the bottom of the retina of the second sensing system. These cells spread from the bottom of the eye to the hypothalamus brain, which controls this body clock.

(Artwork: Sciencemuseum.co.uk) With a healthy body, these cells are most sensitive to green light - unlike the most sensitive visual system for light with green wavelengths. tree. Green light reception is much more effective than green in resetting the subject's body clock.

The study, published in the journal Current Biology , examined two blind subjects: a 56-year-old man and an 87-year-old woman. Although they could not see anything, they did not lose their balance in sleep often associated with blindness . The main author of the study, Steven W. Lockley, assistant professor at Harvard Medical School, Brigham and Women Hospital, Medical Sleep Department said: Most blind people have trouble with the metronome. Sleep , the time they go to sleep and wake up are not in sync with other normal people. Very rare cases like these two, only 10 cases have been confirmed so far. Their sight is not working but the rhythm of sleep is not affected at all.

The study was done by a team from Harvard Medical School, Brigham and Women Hospital, Massachusetts Eye-Tai Hospital, Imperial University London, Oxford University, Thomas Jefferson University and City University. in London. They brought an experimental subject to two separate, green and green light sources - with the maximum wavelength for normal vision. They found that green light does not work in the presence of melatonin - the hormone signals at night and makes us sleepy. Meanwhile, access to green light reduces 57% of melatonin. It also deflects the subject's body clock 1.2 hours and makes the subject more alert (measured by the alpha wave activity of the brain), increased hearing and sleepiness.

The study also showed that the second system also has at least some visual sensitivity. The second object is the woman, she can know when green light shines on her. She told researchers the feeling of " glow ", although she could not detect light at other wavelengths.

The third finding demonstrates that the pupil's contraction before light is mainly controlled by the second system of the eye. Although a woman's eyes are not sensitive to the light of a pen if only for a short period of time - like the pen the doctor uses in their office. Her pupils were indeed shrinking when shining green light for a relatively long time compared to other light.

Lockley said the new study confirms previous research on normal vision subjects. Improved understanding of people's sleep rhythms is a potential strength. Green light can be used to assist recovery when people encounter time zone changes after flights and can help people work at night more alert.

Lockley said: 'A large amount of caffeine consumed in our society shows that we all lack sleep. This affects our activities and learning; In the long run, it can affect health. If we can't get enough sleep, this study suggests that light can be used as an effective measure without medication to treat fatigue. '