Why don't you know the darkness of the night during the day? Three new cells have been discovered in Science today to help the brain distinguish between day and night.

▎ academic longitude / report today, science magazine published a new study from the Salk Institute: Professor Satchidananda panda found three new types of cells in the human body, and pointed out that they can detect the intensity of light and let the brain construct the rhythm of the biological clock.the news headlines of the Salk Institute are easier to understand - these three cells allow the brain to distinguish between day and night.Image Source: a screenshot of the Salk Institute's official website. These cells have a long name called intrinsic photoresponsive retinal ganglion cells (iprgc).from the name, this is a group of light sensitive cells distributed in the retina.in animal models such as mice, people have found the existence of these cells and found their relationship with biological rhythm.however, there has never been any report on this kind of cells in human beings or even other primates.in order to find traces of these cells in humans, the researchers have drawn on the valuable resources of human remains donors.they took the retinas out of the eyes of these donors and placed them on specific devices to study how the cells in the retina would respond to different light conditions.in the study, they found that a small number of cells began to emit electrical signals after 30 seconds of light exposure.and even when the light goes out, some cells remain active for a few seconds.this is the characteristic of photosensitive cells.subsequently, the researchers also examined how different colors of light affected these cells.through detailed analysis, the researchers found three kinds of iprgc: the first kind of cell is very sensitive to light, and it will react quickly, and this reaction can last for a long time; the second kind of cell needs more time to respond to light, and after the reaction is started, it will shut down for a longer time; the third kind of cell will only start and start when the light is very strong It's also very fast.but their activity is not long enough, once the light stops, they will stop working.} brushing your cell phone before bedtime can affect sleep quality (photo source: pixabay) what's the use of these cells? The researchers point out that it answers some questions about the biological clock.we know that light plays a very important role in regulating the biological clock.for example, if you look at the screen of your computer and mobile phone before you go to bed, if you are exposed to too much blue light, it may affect your sleep quality. and the bright sunshine in the morning can also promote us to wake up from a deep sleep and usher in a new day. if light is not visible, the biological clock is prone to be disordered. then, why can some blind people who can't see maintain a good sleep / wakefulness rhythm? The answer may lie in these cells. these blind people may lack cone or rod cells, but they still have iprgc, which is responsible for light sensitivity. it is the presence of these cells that enables them to maintain a good circadian rhythm. + Dr Ludovic MURE (left) and Satchidananda Panda (right) (photo source: Salk Institute) Professor panda, one of the corresponding authors of the study, pointed out that changes in living habits have made human beings more and more "homesick" and less vulnerable to natural light. and understanding the function of these cells can help us design better lighting environment and improve our life. another corresponding author, Dr. Ludovic MURE, points out that the findings also help scientists find drugs to treat related diseases. in the future, these researchers plan to further study the details of these cells. for example, what kind of effect will be produced if you first irradiate orange light and then blue light. in nature, the light color changes in the morning and dusk. understanding the reactions of these cells can also help us better understand our own biological clock. References: [1] Ludovic s. Murre et al. (2019), functional diversity of human inherently photosensive retinal cells, science, DOI: three types of cells help the brain tell day from night, retrieved December 5, 2019, from