Photic resetting of the human circadian pacemaker in the absence of conscious vision

E. B. Klerman, T. L. Shanahan, D. J. Brotman, D. W. Rimmer, J. S. Emens, J. F. Rizzo, C. A. Czeisler

Research output: Contribution to journalArticlepeer-review

113 Scopus citations


Ocular light exposure patterns are the primary stimuli for entraining the human circadian system to the local 24-h day. Many totally blind persons cannot use these stimuli and, therefore, have circadian rhythms that are not entrained. However, a few otherwise totally blind persons retain the ability to suppress plasma melatonin concentrations after ocular light exposure, probably using a neural pathway that includes the site of the human circadian pacemaker, suggesting that light information is reaching this site. To test definitively whether ocular light exposure could affect the circadian pacemaker of some blind persons and whether melatonin suppression in response to bright light correlates with light-induced phase shifts of the circadian system, the authors performed experiments with 5 totally blind volunteers using a protocol known to induce phase shifts of the circadian pacemaker in sighted individuals. In the 2 blind individuals who maintained light-induced melatonin suppression, the circadian system was shifted by appropriately timed bright-light stimuli. These data demonstrate that light can affect the circadian pacemaker of some totally blind individuals - either by altering the phase of the circadian pacemaker or by affecting its amplitude. They are consistent with data from animal studies demonstrating that there are different neural pathways and retinal cells that relay photic information to the brain: one for conscious light perception and the other for non-image-forming functions.

Original languageEnglish (US)
Pages (from-to)548-555
Number of pages8
JournalJournal of biological rhythms
Issue number6
StatePublished - Dec 1 2002
Externally publishedYes


  • Blind
  • Circadian
  • Human
  • Melatonin
  • Phase shift
  • Photic

ASJC Scopus subject areas

  • Physiology
  • Physiology (medical)


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