Dark therapy

Dark therapy, also called scototherapy, light restriction and darkness therapy, is a treatment which involves eliminating all light, or all blue light, in a subject's environment, for a period of several hours prior to bedtime. Dark therapy manipulates the circadian rhythms acting on hormones and neurotransmitters. It has been proposed recently (2005) to combine the chronobiological manipulations of light/dark and/or sleep/wake therapies with psychopharmacological medication for depression as well as for circadian rhythm sleep disorders. In the words of Anna Wirz-Justice:

Light therapy has undergone widespread controlled randomized clinical trials, and wake therapy has been so widely studied over decades that the efficacy data are strong. These nonpharmaceutical, biologically based therapies are not only powerful adjuvants, but also antidepressants in their own right... [P]ilot studies suggest that the simple measure of promoting long nights (more rest, more sleep, no light) can stop rapid cycling in bipolar patients, or diminish manic symptoms—intriguing findings that require replication. (page 223, 226)

Researchers hypothesize that benefits of being in the dark are due to melatonin production by the pineal gland, which occurs when the eyes are deprived of light, as shown during controlled light-dark cycles, even for some blind subjects, indicating that melanopsin is responsible for circadian entrainment in humans.

Humans are diurnal, sleeping at night. Many physiological processes proceed in 24-hour cycles each day, coordinated by the environmental daylight/darkness cycle in nature. People with circadian rhythm disorders do not have the normal relationship to this daily cycle. Their bodily processes may, or sometimes may not, be well-synchronized with each other, but they are not correctly synchronized with the light/dark cycle. Examples are delayed sleep phase disorder, where sleep timing is delayed several hours, and non-24-hour sleep-wake disorder, where the circadian period is longer or, very rarely, shorter than the human average of 24.2 hours.

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