Brushyour phone before bed is prone to depression? The Xue Tian/Zhao Huan team reveals the neural mechanism of night-time blue light "depressing".

▎ what do you usually do before bedtime? If you're always watching TV or staring at your computer or cell phone for a long time, the following research paper, just published online in nature neuroscience, may give you some health tips.a research team led by Professor Xue Tian of China University of science and technology and Dr. Zhao Huan of Hefei University found that increasing blue light at night will affect specific neural circuits of the brain, and cause depression related symptoms.scientists pointed out in their paper that light affects various physiological functions of mammals, including mood.on the one hand, many studies have shown that moderate exposure to solar energy during the day can improve mood, and the use of "phototherapy" to supplement light can alleviate the symptoms of depression patients; on the other hand, excessive light from light pollution or electronic equipment at night is considered to have the risk of causing depression symptoms.although the circadian preference of mice is contrary to that of humans, their behavior is also affected by daily light changes and circadian rhythm.the team first designed experiments to verify this.} schematic diagram of experimental design: mice in the experimental group were exposed to blue light (LAN) at night, and then their behavior changes were observed (photo source: reference [1]). They were exposed to blue light for 2 hours every night for 3 consecutive weeks.after increasing night lighting, the circadian rhythm of mice was not changed, but some abnormal behaviors gradually appeared.for example, when forced to swim, it always gives up; in the face of sugar water, its preference decreases - happy water is not happy! Because these behaviors are similar to human depressive behaviors, scientists define them as depression like behaviors.What's more, the mice did not recover immediately after the blue light irradiation was cancelled every night, and the depression like behavior continued for up to 3 weeks.} the results of forced swimming test and sugar preference test showed that the behavior of mice exposed to blue light at night for a continuous period of time changed (photo source: reference [1]). Then, why does increased light at night cause depression like behavior? Next, the team used neural tracking tools to find a special neural circuit, and then revealed the possible neural mechanism behind the phenomenon.specifically, this neural loop starts from the retina and contains a class of ganglion cells (iprgc), which express a protein related to regulating the biological clock.these cells are sensitive to light, and when activated by light, they send signals to the dorsal perihabenular nucleus (dphb), a part of which then projects to the nucleus accumbens (NAC).and these two brain regions are closely related to depressive symptoms.among them, the lateral habenular nucleus is often referred to as the "counter reward center" of the brain, which mediates many negative emotions. Its hyperactivity will induce depressive behavior; the nucleus accumbens is closely related to pleasure and participates in the formation of depression.when the researchers blocked the neural connection between the lateral habenular nucleus and the nucleus accumbens in the mouse brain, it can prevent the depression like behavior induced by light at night, which indicates that this neural circuit plays an important role.} researchers have proposed a neural pathway for depressive behavior caused by increasing light at night (photo source: reference [1]). Some people may ask, since this neural circuit will be activated by light, what should be done during the day? The authors did not find out why the light intensity during the day was greater than that at night. in the discussion section of the paper, the scientists also pointed out whether this discovery can infer that people still need to think carefully. After all, the mouse experiment has its limitations. For example, mice hate light, so the negative emotion of light may be stronger. moreover, the behavior of not preferring sugar water may also be caused by other reasons, which may not be the same as the real depression of human beings. however, the authors conclude that the first step is to identify the neural pathways through which nighttime light affects the brain in order to understand how increased nighttime light affects mood. if light activates the same neural circuits in the human body, these results may help to explain how excessive nighttime illumination affects humans and why it is associated with depressive symptoms. in fact, not long ago, scientists found iprgc ganglion cells in the human retina, which is the first stop of this neural loop. } related reading: why don't you understand the darkness of the night during the day? Science has found three new cells that can help the brain distinguish between day and night (photo source: pixabay) with the progress of industry and technology, night lighting is becoming more and more common. Many people live under the neon lights of the "city that never sleeps". When the landscape lights go out at night, they return home and continue to accompany the blue light from electronic devices. however, human beings have adapted to the changing light conditions during the course of millions of years. When the light is excessive at night, our health and mood may be affected negatively.