Short-wavelength sensitivity for the direct effects of light on alertness, vigilance, and the waking electroencephalogram in humans

Abstract

Study Objectives: To assess the wavelength-dependent sensitivity of the acute effects of ocular light exposure on alertness, performance, waking electroencephalogram (EEG), and cortisol. Design: A between-subjects design was employed to compare the effects of exposure to 460-nm or 555-nm light for 6.5 hours during the biological night. Setting: Intensive Physiological Monitoring Unit, Brigham and Women's Hospital, Boston, MA. Patients and Participants: Sixteen healthy adults (8 women; mean age ± SD = 23.3 ± 2.4 years). Interventions: Subjects were exposed to equal photon densities (2.8 × 1013 photons · cm-2 · s -1) of either 460-nm (n = 8) or 555-nm (n = 8) monochromatic light for 6.5 hours, 15 minutes after mydriasis. Measurements and Results: Subjects underwent continuous EEG/electrooculogram recordings and completed a performance battery every 30 to 60 minutes. As compared with those exposed to 555-nm light, subjects exposed to 460-nm light had significantly lower subjective sleepiness ratings, decreased auditory reaction time, fewer attentional failures, decreased EEG power density in the delta-theta range (0.5-5.5 Hz), and increased EEG power density in the high-alpha range (9.5-10.5 Hz). Light had no direct effect on cortisol. Conclusions: Short-wavelength sensitivity to the acute alerting effects of light indicates that the visual photopic system is not the primary photo-receptor system mediating these responses to light. The frequency-specific changes in the waking EEG indicate that short-wavelength light is a powerful agent that immediately attenuates the negative effects of both homeostatic sleep pressure and the circadian drive for sleep on alertness, performance, and the ability to sustain attention.