Short-wavelength sensitivity for the direct effects of light on alertness, vigilance, and the waking electroencephalogram in humans.
OBJECTIVE
To assess the wavelength-dependent sensitivity of the acute effects of ocular light exposure on alertness, performance, waking electroencephalogram (EEG), and cortisol.


METHODS
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.


METHODS
Intensive Physiological Monitoring Unit, Brigham and Women's Hospital, Boston, MA.


METHODS
Sixteen healthy adults (8 women; mean age +/- SD = 23.3 +/- 2.4 years).


METHODS
Subjects were exposed to equal photon densities (2.8 x 10(13) photons x cm(-2) x s(-1)) of either 460-nm (n = 8) or 555-nm (n = 8) monochromatic light for 6.5 hours, 15 minutes after mydriasis.


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 photoreceptor 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.
Lockley
Steven W
SW
Division of Sleep Medicine, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, USA. slockley@hms.harvard.edu
Evans
Erin E
EE
Scheer
Frank A J L
FA
Brainard
George C
GC
Czeisler
Charles A
CA
Aeschbach
Daniel
D
D000328:Adult; D001143:Arousal / Q000502:physiology*; D006970:Disorders of Excessive Somnolence / Q000175:diagnosis / Q000453:epidemiology; D004569:Electroencephalography; D005260:Female; D006801:Humans; D006854:Hydrocortisone / Q000097:blood; D008297:Male; D008550:Melatonin / Q000097:blood; D020795:Photophobia; D011597:Psychomotor Performance / Q000502:physiology; D011863:Radioimmunoassay; D020178:Sleep Disorders, Circadian Rhythm / Q000097:blood / Q000453:epidemiology; D014851:Wakefulness
D008550:Melatonin; D006854:Hydrocortisone