Chapter

The phase shift hypothesis and the bio-psycho-social-environmental model

Alfred J. Lewy, Jonathan S. Emens, Jeannie B. Songer, Amber L. Laurie, Neelam Sims, Steven C. Fiala and Allie L. Buti

in Seasonal Affective Disorder

Second edition

Published on behalf of Oxford University Press

Published in print October 2009 | ISBN: 9780199544288
Published online February 2013 | e-ISBN: 9780191754593 | DOI: http://dx.doi.org/10.1093/med/9780199544288.003.0006
The phase shift hypothesis and the bio-psycho-social-environmental model

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In conclusion, the melatonin onset is important in human circadian biology. It is used to determine baseline circadian phase position and (with the melatonin/mid-sleep interval) baseline circadian alignment/misalignment, which can then be used to phase type the individual and to optimize the use of phase-resetting agents by indicating the phase of the PRC. The melatonin onset can also be used to monitor the effects of the phase-resetting agents. The advantages of PAD over just using the melatonin onset or sleep time are discussed elsewhere (Lewy et al. 2009). These include removing the confounding effects from sleep–wake cycles that occur at the different times, removing the possibility that subjects or their raters infer their DLMO clock times from knowledge of sleep times (PAD cannot be inferred from sleep times alone) and the fact that psychiatric symptoms are more likely to be caused by internal circadian misalignment than DLMO clock time. It is possible that the clock time of the melatonin onset may, in certain cases, be a better surrogate marker for the circadian misalignment endotype if the changes in sleep time feed back onto the clock time of the melatonin onset; however, PAD would still be more likely to accurately represent the causal component of the circadian misalignment endotype.

The melatonin onset, particularly the time interval between the melatonin onset and mid-sleep, is the marker of choice for determining whether or not an individual has a circadian component to their sleep or psychiatric disorder. Shifts in the timing of the melatonin onset also provide a way to monitor the use of the two phase-resetting treatments of choice, bright light and melatonin administration. The optimal timing of these treatments is best individualized by scheduling these treatments in relation to the timing of the melatonin onset. Misaligned circadian rhythms may be the first example in psychiatry of a physiological basis and a related laboratory test that provides key information guiding diagnosis, treatment, and follow-up. If the above guidelines prove not to be useful, these patients may need to be assessed on several occasions (no more frequently than once per week) in order to determine if indeed that individual patient has symptoms that correlate with their melatonin/mid-sleep intervals. If such a correlation exists, the above explains how bright light exposure and low-dose melatonin may be helpful.

Chapter.  9741 words.  Illustrated.

Subjects: Psychiatry

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