Written by Joyce Smith, BS. This study provides insight into the effect of blue versus amber wavelength light on the circadian and sleep systems and their potential roles in traumatic brain injury repair and recovery.
Animal models have shown that sleep plays a vital role in brain injury repair 1,2. Restorative sleep is necessary for cognitive function (particularly judgement, decision- making, and executive functions) 3,4 and for maintaining the structural plasticity of synaptic connections 5,6. Kilgore et al, in a current 2020 study, determined that sleep may play a key role in brain repair and recovery in mild traumatic brain injury (mTBI). Kilgore and team in a current randomized, double-blind, placebo-controlled trial 7 tested whether exposure to blue –wavelength light could reset the circadian rhythms and shift the sleep patterns of 32 adults (18-48 years old) recovering from mild traumatic brain injury (mTBI). Each morning the effect of six weeks of daily 30-min pulses of BLUE light (peak λ = 469 nm) on sixteen participants was compared to the effect of AMBER light (peakλ=578 nm) on a control group of sixteen. Neurocognitive assessments, MRI scans, sleep latency tests and questionnaires were done at baseline. Six weeks later, assessments were repeated to evaluate neurocognitive and neuroimaging outcomes, including gray matter volume (GMV); resting-state functional connectivity; directed connectivity using Granger causality; and white matter integrity using diffusion tensor imaging (DTI).
The research team found that restorative sleep is vital for reducing subjective and objective sleepiness and improving cognitive performance among participants recovering from mTBI. Compared to AMBER light, 30 minutes of morning BLUE light was more effective at shifting sleep-wake periods. In fact, at the end of the final week, participants receiving BLUE light generally fell asleep 57.5 minutes earlier (p=0.004) and awakened 55.9 minutes earlier (p=0.037) compared to baseline, while those in the amber group fell asleep 13.8 minutes later (P=0.508) and awakened only 16.1 minutes earlier (p=0.576) compared to baseline. Also BLUE light recipients experienced less daytime sleepiness (p=0.027), were more alert during mid-day and had improved cognitive performance compared to AMBER light recipients. Precisely 87.5% of BLUE light recipients had reduced sleepiness scores compared to 37.5% of AMBER light recipients. Moreover, compared to amber light, the blue light intervention was associated with increases in gray matter volume within the posterior thalamus and greater structural and functional thalamocortical connectivity. Evident, as well, were multiple associations between improvements in cognitive performance and the observed physiological changes. These findings are consistent with the hypothesized function that morning blue wavelength light impacts the circadian rhythm of sleep and alertness, and the postulated role of sleep in accelerating neural repair processes. Together, these findings point to blue wavelength light and its ability to reset circadian rhythms as a potential intervention to support brain repair processes and recovery following brain injury.
Study limitations include a lack of reliable monitoring of participant compliance during blue and amber light treatment, the use of wrist actigraphy instead of nightly polysomnographic sleep recordings, the absence of data on participants who had more than one or multiple concussions, and the fact that analysis only focused on primary outcome variables collected at baseline and after 6 weeks of treatment. However, the research team asserts that their future work will explore actigraphic variables in depth at each week to determine whether sleep outcomes reach their peak before six weeks.
Source: Killgore, William DS, John R. Vanuk, Bradley R. Shane, Mareen Weber, and Sahil Bajaj. “A randomized, double-blind, placebo-controlled trial of blue wavelength light exposure on sleep and recovery of brain structure, function, and cognition following mild traumatic brain injury.” Neurobiology of disease 134 (2020): 104679.
© 2019 Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/BY-NC-ND/4.0/)
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Posted February 17, 2020.
Joyce Smith, BS, is a degreed laboratory technologist. She received her bachelor of arts with a major in Chemistry and a minor in Biology from the University of Saskatchewan and her internship through the University of Saskatchewan College of Medicine and the Royal University Hospital in Saskatoon, Saskatchewan. She currently resides in Bloomingdale, IL.
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- Killgore WDS, Vanuk JR, Shane BR, Weber M, Bajaj S. A randomized, double-blind, placebo-controlled trial of blue wavelength light exposure on sleep and recovery of brain structure, function, and cognition following mild traumatic brain injury. Neurobiol Dis. 2020;134:104679.
