Light Sensitization Study
Condition: Chronobiology Disorders; Circadian Rhythm Disorders; Sleep Disorders, Circadian Rhythm
MeSH terms: Sleep Wake Disorders; Chronobiology Disorders; Sleep Disorders, Circadian Rhythm
Study type: Interventional

Summary: 
      Circadian rhythm disorders are a class of sleep disorders characterized by misalignment
      between the timing of sleep and the timing of rhythms driven by the biological clock. Light
      therapy can effectively treat these disorders, but the intensity and duration of light
      exposure required to do so has limited its practical use. In this study the investigators
      will test whether pre-exposure to dim light may enhance the response of the circadian system
      to light therapy. If so, this could result in shorter treatments that would have greater
      practical applications.
    

Detailed description: 
      Sleep disorders affect 35-40% of adults, resulting in diminished quality of life, and
      increased morbidity, mortality, and risk of automobile and occupational accidents. Circadian
      rhythm sleep disorders form a distinct class of sleep disorders characterized by misalignment
      between the timing of sleep and the circadian pacemaker. While light therapy can be an
      effective treatment of circadian rhythm sleep disorders, there are numerous practical
      limitations.

      Light is the most powerful signal from the environment that influences and regulates daily
      biological rhythms. It is well-established that the irradiance, duration, and timing of light
      exposure all affect the response of the circadian system. While it was once thought that
      these responses were mediated through the visual system, it is now known that there is a
      network of intrinsically photosensitive retinal ganglion cells (ipRGCs) that mediate
      circadian responses to light. Other new studies have demonstrated that recent light exposure
      history affects the circadian response to light in humans.

      These recent findings have important implications for the use of light to treat circadian
      rhythm disorders, including delayed and advanced sleep phase disorders, shift work sleep
      disorder, and jet lag, and they may also have relevance for the use of light to treat
      seasonal affective disorder. Up to now, little attention has been paid to the duration or
      intensity of light exposure prior to such light treatments. The investigators now have
      evidence that the human circadian system can become desensitized to light during long
      exposures and evidence that it can be sensitized to light by prior exposure to dim light.
      These recent findings suggest that light treatment protocols that sensitize the circadian
      system prior to the light treatment will be more effective than those currently in use.

      The 13-day inpatient studies the investigators propose will examine the effect on the human
      circadian system of different durations of dim-light sensitization prior to a standardized
      light treatment. These results will be compared within subjects in a randomized cross-over
      design study in which each subject will receive a control treatment and a light treatment
      with prior dim-light sensitization. The investigators will also include circadian phase
      disorder patients to test these mechanisms in the target patient population. Our findings
      will provide an important step in understanding how new knowledge about the circadian
      photoreceptive system can be used to refine and provide better treatment options for
      circadian rhythm disorders.
    

Intervention name(s): light exposure
Intervention type(s): Other
Intervention description(s): 12-hour light exposure of approximately 200 lux
Allocation: Randomized
Intervention model: Crossover Assignment
Masking: None (Open Label)
Primary purpose: Basic Science
Keywords: light; melatonin; circadian; delayed sleep phase disorder; circadian light sensitivity; circadian timing system