Objective Blue light is a powerful environmental stimulus that can produce significant phase shifts in the circadian rhythm of melatonin and sleep propensity as well as acute effects on alertness of neurobehavioral performance. Here, we undertook an expansion and reanalysis of our previously published findings to examine the effect of acute blue light exposure on the strength of resting-state functional connectivity (rsFC) between a previously identified region of the left dorsolateral prefrontal cortex (DLPFC) and 106 cortical and subcortical regions.Methods Twenty-nine healthy adults (16 men and 13 women; age 18-32 years) completed a psychomotor vigilance test (PVT) before and after a single 30-min exposure to either blue (λ = 469 nm; n = 17) or amber wavelength (λ = 578 nm; n = 12) light, immediately followed by an rsFC scan. ResultsCompared with amber light, blue light exposure produced significantly greater functional connectivity between the left DLPFC seed region and 30 cortical and subcortical regions (P < 0.05; false discovery ratecorrected). Although neurobehavioral performance did not differ between light conditions, only those exposed to blue light showed a significant association between rsFC and sustained PVT performance. Better sustained PVT performance was associated with greater connectivity between the left DLPFC and regions associated with visuospatial awareness/motion detection (right temporaloccipital middle temporal gyrus) and memory (left hippocampus), as well as reduced connectivity in a circuit associated with cognitive rumination and distraction (left parahippocampal gyrus). ConclusionFindings suggest that blue-wavelength light may facilitate acute alertness and improved cognitive performance through enhanced rsFC between the left DLPFC and cortical regions associated with visuospatial awareness.

Introduction Sleep problems are prevalent throughout the population, but little is known about the brain mechanisms that differentiate good and poor sleepers. We studied the association between brain neurochemistry, as measured by proton magnetic resonance spectroscopy (1H-MRS), and sleep quality as measured by actigraphy. We hypothesized that better sleep quality would be predicted by brain metabolites indicative of greater neuronal health, neural inhibition, and reduced levels of excitatory neurotransmitters. Methods 24 healthy adults (12 females25.4±5.6 years) wore an actigraph for seven consecutive days to collect Time in Bed (TIB), Total Sleep Time (TST), Sleep Efficiency (SE), Sleep Onset Latency (SOL), and Wake After Sleep Onset (WASO), and underwent 1H-MRS neuroimaging at 3T. Metabolite data from the medial prefrontal cortex (mPFC), dorsolateral prefrontal cortex (dlPFC), and medial parietal-occipital cortex (P-OCC) were entered stepwise into a series of multiple linear regression models to predict each actigraphic outcome. Results For SE, the regression analysis yielded a significant three predictor model (adjusted R2=.59), p=.0001, including mPFC choline (Cho; β=-.60), P-OCC N-Acetylaspartate (NAA ; β=.56), and P-OCC glutamate+glutamine (Glx; β=-.33). Better SE was associated with a combination of decreased Cho within the mPFC, and increased NAA and decreased Glx within the P-OCC. SOL was predicted by mPFC Cho alone (β =.60; adjusted R2 = .33), p=.002. This suggests that greater Cho within the mPFC was associated with a longer latency to fall asleep. Finally, for WASO, the regression analysis yielded a significant two predictor model, (adjusted R2 = .39), p=.002, including mPFC Cho (β = .56), P-OCC NAA (β = -.41). This suggests that a combination of greater Cho within the mPFC and decreased NAA in the P-OCC was associated with more minutes of wake after sleep onset. Conclusion Sleep quality was predicted from brain metabolites within the medial default mode network (DMN), an interconnected system of cortical regions that is normally deactivated during effortful cognitive processing. Sleep quality was predicted by a combined pattern of metabolites consistent with greater neuronal integrity, reduced cellular turnover, and lower excitatory neurotransmitters. Findings suggest potential metabolic and neuroanatomic targets for enhancing brain health to facilitate sleep quality. Support (If Any)

Introduction Blue-wavelength light can produce phase-shifts in the circadian rhythm. We have previously shown that morning blue light exposure was associated with advanced onset of sleep time and diminished daytime sleepiness. These changes were associated with increased gray matter volume in the left pulvinar nucleus of the thalamus, a key hub of the visual attention network. However, very little is known about the underlying mechanisms of these light activations. We hypothesized that the pulvinar may be affected more by the acute activating effects of light rather than its effects on melatonin. Therefore, we exposed individuals to blue or amber light while undergoing functional neuroimaging at a time of day when melatonin levels are almost non-existent. Methods Twenty-six healthy individuals (15 male; 11 female; age=24.27, SD=6.27) completed a counterbalanced cross-over study involving two 3T functional MRI sessions separated by one week. During scanning, participants were acutely exposed to either continuous blue light (470 nm; active condition) or amber light (580 nm; placebo) while completing an N-Back working memory task. We contrasted the 2-back versus the 0-back condition and compared the blue and amber sessions using a paired t-test in SPM12. Results Acute blue light (versus amber placebo) during a working memory task was associated with significantly greater activation (p&lt;.05) within the left pulvinar nucleus (k=47 voxels; MNI: x=-14, y=-34, z=8), a region nearly identical to that found in our previous work where we found increased volume with six-weeks of daily blue light exposure. Salivary melatonin levels were unchanged by either light condition. Conclusion Acute exposure to blue-wavelength light (versus amber placebo light) activated a key region of the visual attention network that was previously demonstrated to be enlarged by 6-weeks of daily morning blue light exposure. As melatonin levels remained unchanged by the light in this study, the findings point to an underlying neural mechanism that may lead specifically to activation of the pulvinar, which over time may enhance gray matter volume of that structure. These findings suggest a concordance of functional and structural changes induced by blue light exposure, which have been associated with shifts in sleep and circadian rhythms. Support (If Any)

Introduction Amidst the COVID-19 pandemic, widespread feelings of social isolation have become more prevalent than ever before as lockdowns and social distancing measures led people to remain in their homes. The constructs of social isolation and loneliness are similar but reflect slightly different aspects of social experience. Social isolation reflects the amount of social contact a person experiences, whereas loneliness reflects the subjective experience of an emotional yearning for such contact. While is known that sleep problems have increased during the pandemic, there has been little research into the potential effects of social isolation on sleep problems. Here, we examined the influence of social isolation on the extent to which insomnia has interfered with daily life activities. We hypothesized that social isolation would contribute to greater disruption in daily functioning from insomnia, exclusive of the effects of loneliness. Methods 13,298 English-speaking adults from across the U.S. (18-92 years old; 57.5% female) completed an online battery of assessments that included demographic questions, the Insomnia Severity Index (ISI), and the UCLA Loneliness Scale – Version 3 between April 2020 and April 2021. Participants were grouped based on whether they felt “socially isolated” or not at the time of assessment. Social isolation groups were compared for the extent that insomnia interfered with daily functioning, while statistically controlling for loneliness. Results After controlling for loneliness, socially isolated individuals reported much greater daily interference from sleep problems, M=1.58, SD=1.19, compared to those who denied feeling socially isolated, M=0.96, SD=1.04, F(1,13295)=287.67, p=7.5x10-64. Conclusion Social isolation during the pandemic was associated with significantly greater disruption of daily functioning due to sleep-related issues, even after adjusting for self-reported loneliness. Thus, feeling isolated and lacking social contact was related to functional degradation due to sleep problems. Prior evidence suggests that social isolation can have a dramatic negative impact on mental health and can lead to increased all-cause mortality, but these results suggest social isolation may also impact sleep health and functional outcomes (whether that be physical, cognitive, or psychological). Thus, being isolated during the pandemic was associated with greater degradation of functional outcomes of sleep, regardless of subjective loneliness. Support (If Any)