Divergent photic thresholds in the non-image-forming visual system: Entrainment, masking and pupillary light reflex

Matthew P. Butler, Rae Silver

Research output: Contribution to journalArticlepeer-review

50 Scopus citations


Light is the principal cue that entrains the circadian timing system, but the threshold of entrainment and the relative contributions of the retinal photoreceptors-rods, cones and intrinsically photosensitive retinal ganglion cells - Are not known. We measured thresholds of entrainment of wheel-running rhythms at three wavelengths, and compared these to thresholds of two other non-image-forming visual system functions: Masking and the pupillary light reflex (PLR). At the entrainment threshold, the relative spectral sensitivity and absolute photon flux suggest that this threshold is determined by rods. Dim light that entrained mice failed to elicit either masking or PLR; in general, circadian entrainment is more sensitive by 1-2 log units than other measures of the non-image-forming visual system. Importantly, the results indicate that dim light can entrain circadian rhythms even when it fails to produce more easily measurable acute responses to light such as phase shifting and melatonin suppression. Photosensitivity to one response, therefore, cannot be generalized to other non-image-forming functions. These results also impact practical problems in selecting appropriate lighting in laboratory animal husbandry.

Original languageEnglish (US)
Pages (from-to)745-750
Number of pages6
JournalProceedings of the Royal Society B: Biological Sciences
Issue number1706
StatePublished - Mar 7 2011
Externally publishedYes


  • Circadian
  • Photoreceptor
  • Retina
  • Suprachiasmatic nucleus
  • Wavelength

ASJC Scopus subject areas

  • General Immunology and Microbiology
  • General Environmental Science
  • General Biochemistry, Genetics and Molecular Biology
  • General Agricultural and Biological Sciences


Dive into the research topics of 'Divergent photic thresholds in the non-image-forming visual system: Entrainment, masking and pupillary light reflex'. Together they form a unique fingerprint.

Cite this