A study has found that there may be a "simple, safe, and economical" method for pain relief: green light. A new study on animals reveals the biological basis of how this works. Scientists have been exploring the effects of green light pain relief for at least half a decade, uncovering incidental evidence of how exactly it occurs. The new study, led by neuroscientist Yu Long Tang from Fudan University in Shanghai, unveiled the eye cells and brain pathways that support pain relief sometimes felt after exposure to low-intensity green light.
In a series of experiments, researchers discovered that cones and rods—light-sensitive eye cells—contributed to pain relief resulting from green light exposure in both healthy mice and those with arthritis. As is common in scientific research, the scientists disabled certain cells to observe the effects on the animals' pain perception. When these rods were disabled in some mice, those animals showed only partial relief with green light, while mice lacking cones showed no signs of pain relief at all when bathed in green light.
Tang and his colleagues explain in their published research: "We found that the cone photoreceptors in the retina are critical for pain relief with green light, while rods play a secondary role." From there, they tracked the pathway taken by electrical signals from the eye through the brain. After being immersed in green light, the cones and rods stimulated a group of brain cells in the lateral ventral posterior nucleus, which has previously been linked to the pain-relieving effects of bright light in general. In this part of the brain, these neurons express a hormone involved in pain signaling. These cells then relay the message to another brain region called the dorsal raphe nucleus, which modulates pain, effectively reducing the pressure on the experience of intense pain.
Various studies in animals have identified other mechanisms intertwined in the pain-relieving effects of green light, such as pain receptors in the spinal cord—an unsurprising result considering the complexity of the pain experience. Pain involves sensory, physical, and psychological experiences of stimuli and signals bouncing between the brain, spinal cord, and pain receptors. While pain relief in rodents is far from human experiences, this study successfully identified pain circuits in mammalian brains that respond to visual input, enhancing our understanding of a safe and easy way to suppress it.
Tang and his colleagues wrote: "Although it's unclear whether color perception can be compared between humans and rodents, exposure to green light in both humans and rodents reduces pain sensitivity, suggesting shared mechanisms between the two species," noting that other brain areas are likely involved. Additionally, exposing individuals to eight hours of light therapy daily, as the researcher did with mice in this study, is not practical or feasible, making it interesting to see if shorter durations of green light therapy could effectively relieve pain—and how long the effects last.
Some encouraging findings from other studies have emerged. A study conducted on mice indicated that green light pain relief might be long-lasting, extending for four days post-treatment. Recent clinical trials have also reported that a few hours of daily green light therapy reduced pain severity in a small group of fibromyalgia patients and the number of headache days in migraine sufferers. Green light could benefit post-surgery patients, reducing their reliance on painkillers.
Although this treatment may not work for everyone, if these studies can be replicated in more patients, it may pave the way for green light therapy to become an alternative pain relief option. Beyond chronic pain, the results add insight into why spending time in nature is extremely beneficial.
