Continuous Detection of Stimulus Brightness Differences Using Visual Evoked Potentials in Healthy Volunteers with Closed Eyes.

Background/Objectives: We defined the value of a machine learning algorithm to distinguish between the EEG response to no light or any light stimulations, and between light stimulations with different brightnesses in awake volunteers with closed eyelids. This new method utilizing EEG analysis is visionary in the understanding of visual signal processing and will facilitate the deepening of our knowledge concerning anesthetic research. Methods: X-gradient boosting models were used to classify the cortical response to visual stimulation (no light vs. light stimulations and two lights with different brightnesses). For each of the two classifications, three scenarios were tested: training and prediction in all participants (all), training and prediction in one participant (individual), and training across all but one participant with prediction performed in the participant left out (one out). Results: Ninety-four Caucasian adults were included. The machine learning algorithm had a very high predictive value and accuracy in differentiating between no light and any light stimulations (AUCROCall: 0.96; accuracyall: 0.94; AUCROCindividual: 0.96 ± 0.05, accuracyindividual: 0.94 ± 0.05; AUCROConeout: 0.98 ± 0.04; accuracyoneout: 0.96 ± 0.04). The machine learning algorithm was highly predictive and accurate in distinguishing between light stimulations with different brightnesses (AUCROCall: 0.97; accuracyall: 0.91; AUCROCindividual: 0.98 ± 0.04, accuracyindividual: 0.96 ± 0.04; AUCROConeout: 0.96 ± 0.05; accuracyoneout: 0.93 ± 0.06). The predictive value and accuracy of both classification tasks was comparable between males and females. Conclusions: Machine learning algorithms could almost continuously and reliably differentiate between the cortical EEG responses to no light or light stimulations using visual evoked potentials in awake female and male volunteers with eyes closed. Our findings may open new possibilities for the use of visual evoked potentials in the clinical and intraoperative setting.

Effects of red light on sleep inertia.

Introduction: Sleep inertia, broadly defined as decrements in performance and lowering of alertness following waking, lasts for durations ranging between 1 min and 3 hrs. This study investigated whether, compared to a dim light condition (the control), exposure to long-wavelength (red) light delivered to closed eyelids during sleep (red light mask) and to eyes open upon waking (red light goggles) reduced sleep inertia. Methods: Thirty participants (18 females, 12 males; mean age=30.4 years [SD 13.7]) completed this crossover, within-subjects, counterbalanced design study. Self-reported measures of sleepiness and objective measures of auditory performance and cortisol levels were collected on 3 Friday nights over the course of 3 consecutive weeks. Results: Performance improved significantly during the 30-min data collection period in all experimental conditions. Subjective sleepiness also decreased significantly with time awake in all experimental conditions. As hypothesized, performance of some tasks was significantly better in the red light mask condition than in the dim light condition. Performance scores in the red light goggles condition improved significantly after a few minutes of wearing the light goggles. Discussion: The results show that saturated red light delivered through closed eyelids at levels that do not suppress melatonin can be used to mitigate sleep inertia upon waking.

Individually tailored light intervention through closed eyelids to promote circadian alignment and sleep health.

BACKGROUND: Light is most effective at changing the timing of the circadian clock when applied close to the core body temperature minimum. The present study investigated, in a home setting, if individually tailored light treatment using flashing blue light delivered through closed eyelids during the early part of the sleep period delayed circadian phase and sleep in a population of healthy older adults and in those suffering from early awakening insomnia. METHODS: Twenty-eight participants (9 early awakening insomniacs) completed an 8-week, within-subjects study. Twice, participants collected data during two baseline weeks and one intervention week. During the intervention week, participants wore a flashing blue (active) or a flashing red (control) light mask during sleep. Light was expected to delay circadian phase. Saliva samples for dim light melatonin onset (DLMO) were collected at the end of each baseline and intervention week. Wrist actigraphy and Daysimeter, a calibrated light and activity meter, data were collected during the entire study. RESULTS: Compared to baseline, flashing blue light, but not flashing red light, significantly (p<0.05) delayed DLMO. The mean ± standard deviation phase shift (minutes) was 0:06 ± 0:30 for the flashing red light and 0:34 ± 0:30 for the flashing blue light. Compared to Day 1, sleep start times were significantly delayed (by approximately 46 minutes) at Day 7 after the flashing blue light. The light intervention did not affect sleep efficiency. CONCLUSIONS: The present study demonstrated the feasibility of using light through closed eyelids during sleep for promoting circadian alignment and sleep health.

Pulsing blue light through closed eyelids: effects on acute melatonin suppression and phase shifting of dim light melatonin onset.

Circadian rhythm disturbances parallel the increased prevalence of sleep disorders in older adults. Light therapies that specifically target regulation of the circadian system in principle could be used to treat sleep disorders in this population. Current recommendations for light treatment require the patients to sit in front of a bright light box for at least 1 hour daily, perhaps limiting their willingness to comply. Light applied through closed eyelids during sleep might not only be efficacious for changing circadian phase but also lead to better compliance because patients would receive light treatment while sleeping. Reported here are the results of two studies investigating the impact of a train of 480 nm (blue) light pulses presented to the retina through closed eyelids on melatonin suppression (laboratory study) and on delaying circadian phase (field study). Both studies employed a sleep mask that provided narrowband blue light pulses of 2-second duration every 30 seconds from arrays of light-emitting diodes. The results of the laboratory study demonstrated that the blue light pulses significantly suppressed melatonin by an amount similar to that previously shown in the same protocol at half the frequency (ie, one 2-second pulse every minute for 1 hour). The results of the field study demonstrated that blue light pulses given early in the sleep episode significantly delayed circadian phase in older adults; these results are the first to demonstrate the efficacy and practicality of light treatment by a sleep mask aimed at adjusting circadian phase in a home setting.