Sleep Length and Circadian Regulation in Humans
Condition: Sleep Disorders
MeSH terms: Sleep Wake Disorders
Study type: Interventional

Summary: 
      This research will examine why sleep restriction reduces the body clock's response to bright
      light. The results will enable the optimization of the bright light treatment of people who
      suffer from circadian rhythm sleep disorders, which include shift work sleep disorder, jet
      lag, delayed sleep phase syndrome and winter depression, thereby improving public health and
      safety, well-being, mood, mental function, and quality of life.
    

Detailed description: 
      Millions of Americans suffer from circadian rhythm sleep disorders, which include shift work
      sleep disorder, jet lag, delayed sleep phase syndrome and possibly winter depression. These
      conditions are typically characterized by persistent insomnia and/or excessive daytime
      sleepiness, impaired performance, and gastrointestinal distress. These negative symptoms
      result from a misalignment between the timing of the external social world and the timing of
      the internal circadian (body) clock. Circadian rhythm sleep disorders are effectively treated
      with bright light, which phase shifts the circadian clock, thereby realigning it with the
      timing of the external social world.

      It is widely recognized that social influences have led to an increasing prevalence of sleep
      restriction in modern society. We recently demonstrated for the first time that short sleep
      episodes, when compared to long sleep episodes, markedly reduce phase advances to bright
      light. Thus when people cut their sleep short, they inadvertently reduce their circadian
      responsiveness to bright light. The mechanism(s) behind these reduced phase shifts to light
      are unknown. However, there are at least two aspects of short sleep episodes that could be
      responsible for this effect. First, short sleep episodes are associated with partial sleep
      deprivation. Second, as humans sleep with their eyes closed and are usually exposed to light
      when awake, short sleep episodes are also associated with short dark lengths. Our overall
      goal is to determine the biobehavioral mechanisms by which short sleep episodes impair phase
      shifts to bright light. Specific Aim 1 is to determine the effect of partial sleep
      deprivation on phase advances to light, while controlling for dark length. Specific Aim 2 is
      to determine the effect of short dark lengths on phase advances to light while minimizing
      sleep deprivation. We will estimate the timing of the human circadian clock by measuring
      salivary melatonin, a neuroendocrine hormone released from the pineal gland, and collecting
      measures of sleep via actigraphy, and sleepiness, mood, gastrointestinal distress and
      cognitive performance via computerized assessment.

      Characterization of the separate effects of sleep deprivation and dark length on circadian
      phase shifts to light in humans is critical to understanding how humans respond to light
      during their daily life activities. Furthermore, the findings of this research will produce
      important and practical recommendations for avoiding decrements to phase shifts to light,
      thereby optimizing the bright light treatment of circadian rhythm sleep disorders, and thus
      improving public health and safety, well-being, mood, cognitive function, and quality of
      life.
    

Intervention name(s): Bright light box
Intervention type(s): Device
Intervention description(s): Bright light of about 5000 lux, administered while sitting at a desk.
Allocation: Randomized
Intervention model: Crossover Assignment
Masking: Single (Participant)
Primary purpose: Basic Science
Keywords: Circadian Rhythms