Early morning exposure to blue wavelength light can help heal the brain following mild traumatic brain injury (mTBI), new research suggests.
Results of a small, randomized controlled trial showed blue-light therapy improved brain structure and function, cognition, and sleep in this patient population.
“We found that blue-light therapy improved patients’ daytime sleepiness,” study investigator William D. ‘Scott’ Killgore, PhD, told Medscape Medical News. “So those who got the blue light were less sleepy 6 weeks later than they had been at baseline.”
However, he added, it was the changes in brain structure uncovered by the investigation that made the study unique.
“Prior research had shown that if you use blue light in people with mild traumatic brain injuries, it makes them feel less fatigued during the day, but it had not shown the physical changes in the brain that we demonstrated.
“What we’re seeing now is that blue light is changing the actual brain structure by increasing volume in certain areas and increasing myelination of important pathways involved in visual attention,” added Killgore, professor of psychiatry, psychology, and medical imaging at the University of Arizona in Tucson.
Light, Brain Recovery Linked
Sleep has a potent effect on human health, neurobiology, and cognitive function. Despite this connection, however, sleep is not only driven by homeostatic forces, but is inextricably linked with diurnal circadian rhythms of melatonin secreted by the pineal gland.
Retinal light exposure suppresses melatonin production, which is why circulating levels of the hormone drop to near zero during the circadian day, only to rise again as light levels decline in the evening.
This likely explains why humans experience optimal restful and restorative sleep when sleep cycles are closely tied to circadian night.
Sleep may also play an important role in brain repair and recovery after mTBI, as about half of all individuals who suffer such an injury experience chronic sleep disruption and associated cognitive decline. Mild traumatic brain injury is also associated with disturbances in the normal rhythm of melatonin production.
Given these connections between sleep and neural maintenance/repair, sleep disturbances may hinder normal brain recovery following an injury. The investigators hypothesized that they may be able to facilitate recovery from mTBI injury by optimizing the timing and quality of sleep via targeted light exposure, an association that has never been studied directly, they note.
“I got started working in the army, which is very interested in finding ways to help people get better sleep, and we also know that another problem in the army is traumatic brain injury, so I was studying both of these simultaneously,” said Killgore.
“In doing so, I came across a gentleman who was selling a light therapy device. It got me thinking about the role of light in our sleep-wake patterns, and if we could use light to re-entrain circadian rhythm and help people to recover from brain injuries.”
Sleep disruption, he added, is a major issue in mTBI.
“We know that sleep is critical for brain repair, so it seemed that light therapy might be a way to help,” said Killgore.
For the study, the investigators enrolled 32 adults into the randomized, double-blind, placebo-controlled trial. Participants all had a documented history of mTBI in the preceding 18 months, with significant self-reported sleep problems that emerged or worsened following the injury.
After undergoing baseline neurocognitive and neuroimaging assessments, participants all each underwent a 6-week, in-home light therapy regimen. These treatments comprised daily 30-minute pulses of either blue light
(peak λ = 469 nm) or amber placebo light (peak λ = 578 nm) each morning.
As part of the light therapy, patients were instructed to use the light device every morning within 2 hours of awakening, but no later than 11:00 AM. Participants were told to place the light box an arm’s length from the face, at an angle that would allow the light to bathe both sides of the face.
Upon completion of the 6-week study period, patients underwent a final assessment. A variety of neurocognitive and neuroimaging outcomes were assessed, including gray matter volume, resting-state functional connectivity, directed connectivity using Granger causality, and white matter integrity using diffusion tensor imaging. Numerous sleep-related endpoints were also measured.
Participants who underwent blue-light therapy experienced improvement in a number of sleep-related assessments and demonstrated significantly reduced daytime sleepiness (P = .027) than their counterparts in the sham light therapy group.
In addition, 87.5% of blue-light patients experienced reduced sleepiness scores from pre- to post-treatment, compared with only 37.5% of controls who showed no measurable reduction in sleepiness over the same time frame
(P = .003).
The study also demonstrated that participants in the blue-light therapy group were phase-advanced in sleep onset times, falling asleep an average of 57.5 minutes earlier in the final week of the study vs baseline (P = .004).
In comparison, those in the amber-light therapy group fell asleep 13.8 minutes later in the final week compared with baseline (P = .508). After adjusting for a variety of covariates, the odds ratio for demonstrating any phase advancement with blue light was 7.34 relative to amber light (P = .12)
However, the benefits of blue-light therapy did not stop with improved sleep. Executive function also improved after the intervention, as measured by throughput in the Tower Of London task (odds ratio 6.50; 95% confidence interval, 0.41 – 102.15; P = .183).
Finally, blue-light therapy was associated with increased volume of the posterior thalamus, greater thalamo-cortical functional connectivity, and increased axonal integrity of these pathways.
These findings, investigators note, offer insight into the contributions that the circadian and sleep systems play in brain repair. They also suggest that stimulation of the retinohypothalamic systems through daily exposure to morning blue-light therapy may offer an effective way to retrain the circadian system and facilitate recovery in patients with recent mTBI.
The investigators plan to continue this research to see whether blue light improves sleep quality and how such therapy might affect emotional and psychiatric disorders. Killgore believes that most individuals — injured or not — could benefit from correctly timed morning blue-light exposure, a theory he hopes to prove in future studies.
“Ideally, I think we’re finding a way that we can help people recover faster from mild traumatic brain injuries, especially concussions. This is a very easy clinical treatment that you can be applied to other treatments already out there that may help patients to recover faster. The truth is, there’s not a whole lot out there you can do for somebody with a concussion, other than wait it out,” he said.
Timing Is Critical
Commenting on the findings for Medscape Medical News, Helen J. Burgess, PhD, who was not involved in the study, explained that using blue light to balance circadian rhythms is essential for optimizing sleep, among other things.
“We know that the circadian system is this core support system for our biological functioning,” said Burgess, professor of psychiatry and codirector of the Sleep and Circadian Research Laboratory at the University of Michigan in Ann Arbor.
“Therefore, it makes a lot of sense that anything we can do to stabilize circadian timing will optimize our biological functioning, because it means that all of our physiological processes are happening at the ideal biological time,” she added.
The timing of blue-light therapy plays an important role in its overall efficacy.
“Morning light is good for us because it shifts the clock earlier and improves sleep patterns, which Dr Killgore’s study has shown. There’s also evidence to show that blue- light exposure increases serotonin levels in many different areas of the brain.”
Killgore agreed, noting that blue-light therapy may ultimately benefit a larger segment of society that just patients recovering from brain injury.
“Societally, we could all benefit by regulating our circadian rhythms more effectively,” he explained. “As it is now, people stay up late and get blue light at the wrong time in the evenings, and it’s affecting their sleep. So we’d be doing ourselves a service by getting that light in the morning and avoiding it in the evening.”
This study was funded by a grant from the US Army Medical Research and Development Command. Killgore and Burgess have disclosed no relevant financial relationships.