O sweet spot where art thou? Light treatment of Seasonal Affective Disorder and the circadian time of sleep

• Published in: Journal of affective disorders 2006-02, Vol.90 (2), p.227-231
• Main Authors: Murray, Greg, Michalak, Erin E., Levitt, Anthony J., Levitan, Robert D., Enns, Murray W., Morehouse, Rachel, Lam, Raymond W.
• Format: Article
• Language: English
• Subjects: Adolescent; Adult; Adult and adolescent clinical studies; Aged; Antidepressive Agents, Second-Generation - administration & dosage; Biological and medical sciences; Circadian Rhythm - drug effects; Combined Modality Therapy; Depression; Female; Fluoxetine - administration & dosage; Follow-Up Studies; Humans; Male; Medical sciences; Middle Aged; Miscellaneous; Mood disorders; Phototherapy; Psychology. Psychoanalysis. Psychiatry; Psychopathology. Psychiatry; Risk Factors; Seasonal Affective Disorder - therapy; Sleep - drug effects; Temperature; Wakefulness - drug effects
• ISSN: 0165-0327; 1573-2517
• DOI: 10.1016/j.jad.2005.10.010

This study investigated Lewy's Phase Shift Hypothesis (PSH) for winter Seasonal Affective Disorder, which asserts that the phase angle difference (PAD) between circadian and sleep rhythms is critical in the mechanism of light's therapeutic action. Specifically, we sought to test whether a euthymic "sweet spot" could be identified at a PAD (between temperature minimum and wake time) of circa 3 h. After a baseline week, symptomatic SAD patients ( N = 43) received 8 weeks of morning light treatment. Analyses were based on SIGH-SAD ratings made at baseline and posttreatment. Also estimated pre- and posttreatment were T min (calculated from an algorithm based on Morningness–Eveningness self-report scores), and the phase of the sleep–wake rhythm (as assessed by daily sleep logs). It was predicted that a quadratic relationship would exist between PAD and depression ratings at baseline and posttreatment, with lowest levels around PAD = 3 h. It was further predicted that shift towards PAD = 3 h with treatment would be associated with decreases in depression with treatment. Although trends were in the expected direction, none of the three predictions were supported. Findings are discussed in terms of the study's limitations and the experimental challenge of parsing independent and interacting contributions of sleep and circadian phase.