Killgore WDS, et al. - Considering that sleep and circadian rhythms are among the most robust yet least understood contributors to cognitive performance and brain health, researchers conducted this randomized, double-blind, placebo-controlled trial to capitalize on the circadian reset impact of blue-wavelength light to phase shift the sleep patterns of adult patients (n = 32), aged 18 to 48 years, recovering from mild traumatic brain injury (mTBI), with the intention of facilitating recovery of brain structure, connectivity, and cognitive performance. They contrasted 6-weeks of daily 30-min pulses of blue light (peak λ = 469 nm) each morning vs amber placebo light (peak λ = 578 nm) on neurocognitive and neuroimaging results, involving gray matter volume (GMV), resting-state functional connectivity, directed connectivity using Granger causality, and white matter integrity using diffusion tensor imaging. During a 6-week randomized placebo-controlled trial of daily light exposure, the authors discovered that 30 minutes of morning blue-wavelength light was more powerful compared with amber-wavelength placebo light at shifting sleep-wake periods, decreasing subjective and objective sleepiness, and improving cognitive performance among mTBI-recovering participants. In addition, compared with amber light, the blue light intervention was related to increased GMV within the posterior thalamus (ie, pulvinar) and greater structural and functional thalamocortical connectivity, as well as multiple correlations between improvements in cognitive performance and the observed physiological changes, relative to amber light. Such results provide insight into the brain repair contributions of the circadian and sleep processes and lay the groundwork for therapies directed at the retinohypothalamic system to promote recovery from injury.