Anna Wirz-Justice describes chronotherapy as “controlled exposure to stimuli that act on biological rhythms (such as light) or direct manipulation of sleep to treat psychiatric disorders”.
The first “law” of chronobiology in medicine is to make use of what is available – sleep & wake. If this is done, then we are much more likely to cause remission of illness. The second “law” of chronobiology in medicine is that we ought to cause sustained entrainment through the natural means of regular zeitgebers. A zeitgeber is an external or environmental cue that synchronizes one’s biological rhythms. So we should cause more light, and we should ensure better darkness!
Chronotherapeutic combinations are flexible and should be implemented step-by-step according to the patient’s response. Concomitant antidepressants might be included in order to provide treatment as usual. Chronotherapeutic options usually begin with light therapy for patients who cannot sustain wake therapy. A second step is light therapy combined with a single night’s sleep deprivation. A third step includes a 3-day phase advance.
The full combination of light therapy, 3 times wake therapy, and 3-day sleep phase advance will not be necessary or feasible in all cases, but it can be the trigger for complete symptom remission in major depression.