The goal of this study is to understand factors that contribute to delayed sleep wake phase disorder (DSWPD). The investigators will examine whether patients with DSWPD exhibit alterations in circadian rhythms and sensitivity to light compared to healthy controls. The investigators will also test a new method of predicting circadian rhythms form a blood sample.

• The research parts of the study are 6.5 weeks long and the study, including screening visits, involves 6 in-person visits to the Boulder campus.

• If participants qualify for the study and choose to participate, there will be two visits where participants will pick up research equipment to wear at home for 1-2 weeks of ambulatory monitoring before being studied in the laboratory. The first ambulatory monitoring session is for 2 weeks and the second is one week.

  • On the first ambulatory monitoring session the investigators will have participants answer questions about participant's mood and cognition.
  • On both ambulatory monitoring sessions, the investigators will also ask participants to wear a blood sugar monitor and track the timing of when participants eat using a phone app. The investigators will also have participants wear a wrist worn sleep and light monitor plus a daily sleep log and Google form of when participants go to bed and wake up.

• Next will be a visit where participants will spend 66 hours (2.75 days) in the laboratory.

  • While living in the lab, participants will not be aware of the time of day (e.g., no clocks, internet, cell phones), and the investigators will schedule participant's activities.
  • The investigators will ask participants to remain seated in bed and awake for up to ~39 hours, with the head of the bed raised. Participants will be studied under dim light similar to candlelight.
  • The investigators will frequently take saliva samples for more than 24 hours when the investigators will ask participants to stay awake. The investigators will also take four blood samples.
  • The investigators will also ask participants to perform reaction time tests, tests of participant's ability to think, and to complete ratings of how participants feel multiple times each day that participants are in the lab.
  • The investigators will also record participant's brain wave activity, muscle activity, eye movements, and heart rate when participants stay awake and during ~9h sleep opportunities.

• The investigators will then ask participants to sleep normally at home for ~2 weeks, followed by 1 week of ambulatory monitoring.

• Finally, there will be a visit where participants will spend 48 hours (2 days) in the laboratory.

  • While living in the lab, participants will not be aware of the time of day (e.g., no clocks, internet, cell phones) and the investigators will schedule participant's activities.
  • The investigators will expose participants to different light levels (dim light similar to candlelight and typical room light).
  • The investigators will frequently take saliva samples.
  • The investigators will also ask participants to perform reaction time tests, tests of participant's ability to think, and to complete ratings of how participants feel multiple times each day that participants are in the lab.
  • The investigators will also record participant's brain wave activity, muscle activity, eye movements, and heart rate when participants are awake and while participants sleep.

Inclusion Criteria:

• Delayed sleep wake phase disorder diagnosis
• Altitude history: currently residing at Denver altitude or higher
• BMI normal to moderately overweight

Exclusion Criteria:

• Recent medical condition
• Psychiatric disorder
• Sleep disorder
• Medication use