title: Human phase response curve to a single 6.5 h pulse of short-wavelength light.
abstract: The photic resetting response of the human circadian pacemaker depends on the timing of exposure, and the direction and magnitude of the resulting shift is described by a phase response curve (PRC). Previous PRCs in humans have utilized high-intensity polychromatic white light. Given that the circadian photoreception system is maximally sensitive to short-wavelength visible light, the aim of the current study was to construct a PRC to blue (480 nm) light and compare it to a 10,000 lux white light PRC constructed previously using a similar protocol. Eighteen young healthy participants (18-30 years) were studied for 9-10 days in a time-free environment. The protocol included three baseline days followed by a constant routine (CR) to assess initial circadian phase. Following this CR, participants were exposed to a 6.5 h 480 nm light exposure (11.8 μW cm(-2), 11.2 lux) following mydriasis via a modified Ganzfeld dome. A second CR was conducted following the light exposure to re-assess circadian phase. Phase shifts were calculated from the difference in dim light melatonin onset (DLMO) between CRs. Exposure to 6.5 h of 480 nm light resets the circadian pacemaker according to a conventional type 1 PRC with fitted maximum delays and advances of -2.6 h and 1.3 h, respectively. The 480 nm PRC induced ∼75% of the response of the 10,000 lux white light PRC. These results may contribute to a re-evaluation of dosing guidelines for clinical light therapy and the use of light as a fatigue countermeasure.
authors.affiliation: Circadian Physiology Program, Division of Sleep Medicine, Brigham and Women's Hospital, Harvard Medical School, 221 Longwood Avenue, Boston, MA 02115, USA. mrueger@rics.bwh.harvard.edu
authors.forename: Melanie
authors.initials: M
authors.lastname: Rüger
authors.forename: Melissa A
authors.initials: MA
authors.lastname: St Hilaire
authors.forename: George C
authors.initials: GC
authors.lastname: Brainard
authors.forename: Sat-Bir S
authors.initials: SB
authors.lastname: Khalsa
authors.forename: Richard E
authors.initials: RE
authors.lastname: Kronauer
authors.forename: Charles A
authors.initials: CA
authors.lastname: Czeisler
authors.forename: Steven W
authors.initials: SW
authors.lastname: Lockley
mesh_terms: D000293:Adolescent; D000328:Adult; D001831:Body Temperature; D002940:Circadian Rhythm / Q000502:physiology*; D005260:Female; D006801:Humans; D008027:Light; D008297:Male; D008550:Melatonin / Q000502:physiology; D055815:Young Adult
chemical_list: D008550:Melatonin