Green light appears to relieve pain, and a new study in mice shows why

Green light appears to relieve pain, and a new study in mice shows why

Research suggests there may be a “simple, safe and economical” way to relieve pain: the green light. And a new animal study reveals the biological underpinnings of how it works.

Scientists have been exploring the analgesic effects of green light for at least half a decade, occasionally uncovering a clue as to exactly how it happens.

This new mouse study, led by neuroscientist Yu-Long Tang of Fudan University in Shanghai, reveals the eye cells and brain pathways that underlie the pain relief sometimes experienced after exposure to green light from low intensity.

In a series of experiments, the researchers found that cones and rods – eye cells that detect light – contributed to the analgesic effects of green light in healthy mice and mice with inflamed joints.

As scientists often do, the researchers inactivated certain cells to see what effect this had on the animals’ pain sensation. When they inactivated rods in some mice, these animals showed only partial relief with green light, while mice without cones showed no signs of pain relief when bathed. in a verdant glow.

“We found that retinal cone photoreceptors are essential for green light analgesia, while rods play a secondary role,” Tang and colleagues explain in their published paper.

From there, they followed the path taken by electrical signals from the eye through the brain.

Bathed in green light, the cones and rods stimulated a cluster of brain cells in the ventrolateral geniculate nucleus, which has previously been linked to the analgesic effects of bright light in general.

In this part of the brain, these neurons express a hormone involved in pain signalling. These cells then relay the message to another part of the brain called the dorsal raphe nucleus which modulates pain, effectively lowering the dial on intense pain sensations.

Different animal studies have identified other mechanisms related to the analgesic effects of green light, such as pain receptors in the spinal cord – which is not surprising given the complexity of the pain experience. It involves the sensory, bodily, and psychological experience of stimuli and signals bouncing between the brain, spinal cord, and pain receptors.

While pain relief in rodents falls far short of that in humans, this study succeeds in identifying pain circuits in the mammalian brain that respond to visual input and expands our understanding of a safe and easy way to address them. possibly appease.

“Although it is unclear whether color perception is comparable between humans and rodents, exposure to green light in humans and rodents reduces pain sensitivity, suggesting the involvement of shared mechanisms between the two species,” write Tang and his colleagues, noting that other regions of the brain are likely involved.

Exposing people to eight hours of light therapy a day, like the researcher did for the mice in this study, just isn’t practical or feasible, so it would be interesting to see if shorter bouts of green light therapy are effective in relieving pain – and for how long.

On this point, there are encouraging results from other studies. An animal study in rats suggested that pain relief from green light may be long-lasting, lasting for four days after treatment.

Recent clinical trials have also reported that a few hours of green light therapy each day reduced pain intensity in a small group of fibromyalgia patients and the number of headache days in migraine sufferers. Chronic low back pain is another target. The green light could benefit patients after surgery, reducing their dependence on painkillers.

Although it may not work for everyone, if these studies can be repeated in more patients, it could pave the way for green light therapy to become an alternative option for pain relief.

The lingering challenge is that chronic pain is a difficult beast to tame and not all pain is the same. Opioids are also incredibly effective at relieving pain but are highly addictive, and we don’t yet know how the green light compares.

Besides chronic pain, the findings add color to our understanding of why spending time in nature is so enjoyable. The cocoon of a forest, deep green, could calm our nervous system in more ways than one.

The study was published in Science translational medicine.

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