杏吧原创

BILLIONS of dollars have been spent in search of treatments for psychiatric conditions and brain disorders, when a cheap and effective drug may have been right under our noses: light. Now hospitals are turning to light to treat depression, strokes and Parkinson鈥檚 disease, using it to hit the reset button on our internal clocks.

From green light soothing the pain of migraine, to blue light reducing organ damage during surgery, recent small studies have uncovered some intriguing effects of this therapy. But apart from easing seasonal affective disorder, we鈥檝e been slow to embrace light as a serious contender for treating neurological conditions.

We鈥檝e known for 15 years that a special kind of receptor in our eyes transmits information directly to the body鈥檚 master clock, as well as other brain areas that control mood and alertness. These cells are particularly responsive to bluish light, including sunlight.

These receptors enable light to act as a powerful reset switch, keeping the clock in our brain synced to the outside world. But this clock can fall out of sync or weaken as part of ageing or a range of disorders 鈥� a problem doctors are now starting to treat with light.

Most hospitals have small windows and 24-hour lighting, both of which might exacerbate health problems. To tackle this, several hospitals in Europe and the US are installing dynamic 鈥渟olid state鈥� lighting, which changes like daylight over the course of a day. Such lights can, for example, shine bright whitish-blue in the morning, grow warmer and dimmer throughout the day, and turn orange or switch off at night.

But it hasn鈥檛 been clear if such lights make a difference to health. Now Anders West at Glostrup Hospital in Copenhagen and his team have shown it helps people recover from strokes.

Up to a third of people are depressed in the weeks following a stroke, while up to three-quarters experience fatigue and poor sleep. 鈥淭hese symptoms can have an adverse effect on cognitive function, recovery and survival,鈥� says West.

鈥淚 think we鈥檙e going to see a complete revolution in lighting and architecture in a very short space of time鈥�

He presented data at the Society for Light Therapy and Biological Rhythms conference in Berlin in June, which showed that people recovering from strokes score lower for depression and fatigue, and show more robust circadian rhythms when exposed to solid state lighting. 鈥淭he effect was comparable to giving patients antidepressants,鈥� says West.

Hospital lighting also seems to have a dramatic effect on severe depression, which often involves a disrupted circadian clock with delayed sleep periods. At the Berlin conference, of the Psychiatric Centre in Copenhagen showing that people being treated for severe depression were discharged almost twice as quickly if their rooms faced south-west in comparison with those whose rooms had a north-west aspect. Depending on the time of year, the intensity of daylight in the south-west rooms was 17 to 20 times brighter.

鈥淭hese are very depressed patients who tend to stay in their rooms and isolate themselves, so they鈥檙e more exposed to differences in light intensity,鈥� says Martiny. The 67 people in the study had been randomly assigned rooms, and those who stayed in the brighter rooms were discharged after 29 days on average, compared with nearly 59 days for those in darker rooms.

鈥淲e don鈥檛 know the precise mechanism, but I think it鈥檚 to do with exposure to the morning light, which advances and stabilises their sleep-wake cycles,鈥� says Martiny. His team鈥檚 findings are now informing the design of a new psychiatric centre, due to open in Copenhagen in 2022.

Using light to alter circadian rhythms could also help Parkinson鈥檚 disease. 鈥淥ne of the main challenges for people with Parkinson鈥檚 disease is that they keep waking up in the night, and a lot of them also have problems staying awake in the daytime,鈥� says at Massachusetts General Hospital in Boston.

In previous work, his team found that the rhythmic expression of certain genes was flattened in Parkinson鈥檚 disease, suggesting a sluggish circadian clock. So Videnovic decided to try treating people with the condition using a light box that emits bright white light twice a day, for two weeks. The idea wasn鈥檛 to shift the timing of the clock, but to strengthen it.

The study, published earlier this year, found that those exposed to the bright light slept better at night and were less sleepy and more active in the day, compared with people given a dim red light box as a control (JAMA Neurology, ). The team also saw improvements in some of the movement symptoms of early Parkinson鈥檚 disease.

鈥淲e鈥檙e at such an interesting time,鈥� says at Thomas Jefferson University in Philadelphia. 鈥淥n the one hand, solid state lighting has emerged that is exquisitely tunable, and can do numerous things,鈥� he says. 鈥淎t the same time, there鈥檚 a matured understanding that light truly affects health.鈥�

Brought together, this provides a very exciting opportunity, says Brainard. 鈥淚 think we鈥檙e going to see a complete revolution in lighting and architecture in a very short space of time.鈥�

This article appeared in print under the headline 鈥淭he light way to better brain health鈥�