Ever felt down after staring at your phone late in bed? It's not just you – mice do too

Blue light at night, shepherd's not right

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Lab mice don't have much to laugh about but scientists in China have found new ways of making them depressed – and it's not good news for anyone that loves some screen time before shut-eye.

A team from the University of Science and Technology of China has found that mice exposed to two hours of blue light each night for weeks showed depressive-like behaviour.

The team had a paper published in Nature Neuroscience that ventures that understanding the neural pathway responsible for this could provide insight into how exposure to excessive light at night affects humans.

For some time scientists have known that exposure at night – from light pollution or electronic devices – can seem to cause depressive symptoms. But the neural mechanisms underlying this effect of night-time light have so far been unknown.

Step forward, Tian Xue and his fellow boffins. Their mice were on the receiving end of two-hour doses of blue light at night for three weeks. The study found it took up to three weeks for the animals to gradually develop depressive-like behaviour.

For a lab mouse, depressed behaviour means a tendency to try to escape and decreased preference for sugar, which is weird because depressed humans make a beeline for a mountain of Toblerone and such like when they feel down. Anyway, mice depressed by night-time light are unlikely to cheer up until about three weeks following the end of the experiment, the data indicated.

The researchers said that a specific neural pathway could explain these results: a connection between a specific type of light receptor in the retina to two brain areas, the dorsal perihabenular nucleus and the nucleus accumbens. How did they test the idea? They blocked connection between these two areas and found that those mice with blocked neurons did not show the depressive behavioural changes induced by night-time light.

The authors also found that light exposure at night activated this pathway much more strongly than light during the day and concluded the finding may explain why daytime light exposure did not seem to cause the same kind of depression.

So, it seems that there is a choice. If you want help avoiding depressed moods, don't look at your phone screen or go gaming late into the night. Alternatively, do those things and go to find yourself a backstreet neurologist to administer synaptic injections to block certain neurological transmissions. Just kidding. Don't do that. Please. ®


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