(I-336) Efficacy of Nine (Quasi-) Monochromatic Stimuli on Cognition and Alertness

Introduction:: Recent studies have shown that different wavelengths such as blue, white, and red can have a positive impact on mental and cognitive health. In the present study, a light intervention was designed to test the efficacy of nine (quasi-)monochromatic stimuli on 138 healthy young adults. The goal of the study was to identify the most efficient lighting scheme to improve attention measured with a Go/No Go computerized task and subjective alertness measured with the Karolinska Sleepiness Scale (KSS). This study also investigated alteration in brain electroencephalography (EEG) from the varying stimuli. It was hypothesized that longer wavelengths would improve cognitive task scores, reduce alpha peak frequency, decrease subjective sleepiness, and consequently improve alertness. This research study has the potential to yield both direct and indirect benefits. The direct benefits of this study are to explain how light affects the brain beyond the immediate outward response and facilitate the implementation of optimized lighting schemes in workplaces to enhance alertness. Additionally, the indirect benefits could be significant, as the study's findings may offer insights into the use of light to enhance the efficacy of established treatments for conditions like depression, anxiety, and migraines.


Materials and Methods:: A total of 138 participants were enrolled in this study. Over the course of the study, participant groups were exposed to one of nine wavelengths: (632 nm, 451nm, 523 nm, 499 nm, 593 nm, 474 nm, 621 nm, 479 nm, 555 nm) at one of four illuminances: (< 2 lux, 5 lux, 75 lux, 150 lux). At varying timepoints throughout each session, Karolinska Sleepiness Scale (KSS) and auditory Go/No Go task (GNG) were administered. The KSS test is a subjective sleepiness scale whereas the GNG task is an attention and memory measure. Electroencephalography (EEG) data was also collected throughout the experimental sessions using a 10-20 international system electrode placement with eight electrodes. The EEG data was collected in 270 second bursts and was pre-processed and cleaned in Matlab. The KSS and GNG data were normalized using the first time point and the dim condition, respectively. Outliers were removed using interquartile ranges. Kruskal Wallis followed by Dunn's test was used to determine significance. Standardized low-resolution brain electromagnetic tomography (sLORETA) was used to identify specific brain regions that were either activated or inhibited by the varying lighting conditions. Alpha peak differences between lighting conditions were analyzed in R to determine the alerting effects of each lighting condition. The peak alpha frequency was defined as the frequency with the greatest power spectral density (PSD) in the alpha band, which is defined as the frequencies between 8 and 12 Hz.


Results, Conclusions, and Discussions:: Findings of the present study suggest that performance task was greatly impacted by longer wavelengths (red) at lower illuminances (5 and 75 lux) compared to shorter wavelengths (teal) (p < 0.05, p=0.04), whereas subjective sleepiness was substantially impacted by medium wavelengths (green) compared to shorter wavelengths (sapphire) (p=0.04). This study also found that longer wavelengths, such as red-orange and amber, excited brain regions involved in the modulation of alertness, and cognition, while middle range wavelengths, such as green, inhibited motor brain regions. A mixed model associating KSS score to color and illuminance showed that color was a significant predictor. The colors blue (β = 0.74, p = 0.021), sapphire (β = 0.66, p = 0.038), cyan (β = 0.65, p = 0.047), amber (β = 0.77, p = 0.024), and red-orange (β = 0.70, p = 0.025) all had significantly higher KSS scores compared to green, when controlling for illuminance and within-subject correlation. A mixed model of the GNG scores’ association with color and lighting condition revealed no significant predictors. However, lighting condition and alpha peak frequency were significantly negatively associated (β = -0.10, p = < 0.001) in this model. These findings have significant implications for how lights can be utilized to enhance alertness. If workplaces are seeking out strategies to promote alertness, a longer wavelength of light should be administered whereas if a more relaxing sensation is desired, a middle-ranged wavelength, such as green, should be employed. Previous studies have suggested that green light may alleviate migraines, and our findings provide further support for this hypothesis by demonstrating its ability to inhibit brain activity. This is the first study to identify which brain regions are impacted by differing wavelengths of light at varying illuminances.


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