0038 Acute Blue Light Exposure Increases Activation in the Pulvinar Nucleus

Abstract

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<.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)