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.
Division of Sleep Medicine, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, USA. slockley@hms.harvard.edu
Steven W
SW
Lockley
Erin E
EE
Evans
Frank A J L
FA
Scheer
George C
GC
Brainard
Charles A
CA
Czeisler
Daniel
D
Aeschbach
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