What do you usually do before you go to bed? If you’re always watching TV for long periods of time or staring at your computer or cell phone, the following research paper, just published online in Nature-Neuroscience, may give you some health warnings. A team of researchers led by Professor Xue Tian of the University of Science and Technology of China and Dr. Zhao Huan of Hefei University found that increasing blue light at night can affect specific neural loops in the brain, leading to depression-related symptoms.
Light affects various physiological functions of mammals, including emotions, the scientists note in their paper. On the one hand, many studies have shown that moderate amounts of solar energy during the day boost mood, and that the use of “light therapy” to supplement light can relieve symptoms in depressed patients, and on the other hand, light pollution or excessive light from electronic devices at night is considered to be at risk of causing depressive symptoms.
Although the mice’s day and night preferences were the opposite of those of humans, their behavior was also affected by daily light changes and circadian rhythms. The team first designed experiments to verify this.
Design diagram: Mice in the experimental group increased blue light exposure (LAN) at night and then observed their behavioral changes (Photo: Resources 1)
They were exposed to blue light for 2 hours each night for three consecutive weeks. With increased night time lighting, the circadian rhythms of the mice were not altered, but some unusual behavior gradually emerged. For example, when forced to swim, it is a love of the state of abandonment; Because these behaviors are similar to those in humans, scientists define them as depressive-like behaviors.
Not only that, but the mice did not recover immediately after the nightly blue light was removed, and the depressive behavior continued for up to three weeks.
Results from the Forced Swimming Experiment and the Sugar Water Preference Experiment showed a change in the behavior of mice after exposure to blue light for a period of time (Photo: Supplied)
So why does increased light at night cause depression-like behavior? Next, the team used neural tracing tools to find a special neural loop that revealed the possible neural mechanisms behind the phenomenon.
Specifically, this neural loop begins in the retina and is distributed with a class of neurokerasis cells (known as ipRGC) that express a protein associated with regulating the biological clock. These cells are sensitive to light, and when they are activated by light, they send signals to the back side of a nuclear clump in the brain called the outer nucleus (dorsal perihabenular nucleus, or dpHb), where a portion of the nerve cells are then projected into the voltaid nucleus (NAc). These two brain regions are closely related to depressive symptoms. Among them, the outer nucleus is often referred to as the “anti-reward center” of the brain, which mediates many negative emotions, and its hyperactivity induces depression-like behavior;
When researchers blocked the neural connection between the outer nucleus and the voltion nucleus in the mouse brain, it prevented nocturnal light-inducing depressive behavior, suggesting that the neural circuit played an important role.
The researchers suggested a neural pathway for depression-like behavior caused by increased light at night (Photo: Supplied)
Some one might ask, since this neural loop is activated by light, what about the day? The study authors compared the night time light to this neural loop much more active than daytime light, which may explain why daytime light does not cause behavioral changes.
In the discussion session of the paper, the scientists also pointed out that the findings can infer that humans need to think carefully, after all, the mouse experiment has its limitations, such as the mice themselves are more hate of light, so the negative emotions about light may be extra strong. Moreover, behaviors such as the preference for sugary water may also be caused by other causes, not necessarily the same as the true depression of humans.
However, the authors conclude that to understand the effects of increased light at night on mood, finding out the neural pathways that night light affects the brain is the first step. If light activates the same neural loops in the human body, these results may help explain how excessive night time light affects humans and why they are associated with depressive symptoms. In fact, not long ago, scientists found ipRGC nerve cells in the human retina, the first stop of this neural loop.
With the progress of industry and technology, night lighting is becoming more and more common, many people live in the “night city” under the neon lights, to the landscape lights go out late at night, back home and continue to accompany the electronic devices with the blue light. However, humans have adapted to the light of day and night changes over millions of years of evolution, and our health and mood may be quietly negatively affected when the night light is excessive.