INTRINSICALLY PHOTOSENSITIVE RETINAL GANGLION CELLS AND ITS ROLE HUMAN ALERTNESS
LALITHA SAHI NANDINI WUPPUKONDUR
MASTER OF SCIENCE IN VISION SCIENCE
PACIFIC UNIVERSITY, 2019
PURPOSE: To investigate if exposure to cool (blue) light with a peak wavelength at 450nm can affect alertness, performance and EEG brain waves.
METHODS: Twenty healthy individuals were studied in a balanced cross-over design with exposure to two different light settings of equal illumination (1000 lux): cool blue light (7000K, peaked at 450nm) vs. warm orange light (1800K, peaked at 612 nm). Morning or afternoon sessions had 30-minute dark adaptation and 30-minute light exposure. Alertness was quantified by accuracy and reaction time in a two-back memory task, and performance was quantified by accuracy in a memory recall task (word pair task). Amplitudes of EEG brain waves (delta, theta, alpha, beta, and gamma) were measured during the one hour using a MUSE headband with two temporal (TP9, TP10) and two frontal electrodes (AF7, AF8). Paired t-tests compared the differences between the dark adaptation and experimental light. Mixed model Analysis of covariances was used to compare color temperatures. Factor analysis was used to reduce the dimensionality of the 16 different brain waves and locations.
RESULTS: Exposure to cool light showed a faster reaction time on the two-back memory task (Mean Blue light =1226.3, Mean Orange Light =1317.9,Effect size= 0.5 ) and a Word-Pair task had higher performance (Mean Blue light =81.8 %, Mean Orange Light =78.4 %, Effect size= 0.9) when compared to warm light at p < 0.05. Accuracy on the two-back memory task did not differ significantly between light conditions. Increase in amplitudes from dark adaptation to light was seen in TP gamma and beta factor (Mean Blue light =0.28, Mean No light= -0.40, Effect size=0.74)in cool light (p=0.002) but not in warm light (p=0.5). Theta, delta and alpha factor showed increase in amplitudes in both AF and TP with warm light exposure (Mean Orange light=0.01, Mean No Light= -0.45, Effect size=0.56, p < 0.05) but not in cool light. EEG during learning word pairs, factor AF 8 theta, delta, and alpha showed an increase in amplitudes in both cool light and warm light conditions (p < 0.05). During the two-back task, increase in amplitudes of AF8 beta and gamma was seen under warm light.
CONCLUSION: Our findings from the performance in the two-back memory task, the word pair task as well as the EEG data recorded during the tasks suggest that exposure to cool light may enhance the alertness and performance relative to warm light. Results were consistent with the hypothesis that these effects may be mediated by Intrinsically photosensitive Retinal Ganglion Cells which are sensitive to 450 - 480 nm light.
KEYWORDS: Non-image functions of light, IpRGC, EEG Brain waves, Alertness.
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