Seasonal affective disorder is a subtype of depression or bipolar disorder in which symptoms appear at specific times of the year and go into full remission at other times. In this video, I discuss some of the hypothesized neurobiological mechanisms underlying seasonal affective disorder.

TRANSCRIPT:

Seasonal affective disorder is a subtype of depression or bipolar disorder in which symptoms appear at specific times of the year and go into full remission at other times. The condition most commonly develops during fall or winter, but spring or summer cases do also occur. In order to be diagnosed with seasonal affective disorder, someone must meet the criteria for major depressive disorder or bipolar disorder, but also display seasonal patterns with their symptoms for at least two years.

The mechanisms underlying seasonal affective disorder are not fully understood, and are likely not the same in every case. One hypothesis is that seasonal affective disorder is linked to a disruption in circadian rhythms, the 24-hour cycles that regulate the function of our bodies. According to this hypothesis, in some individuals circadian rhythms may not adjust appropriately when the length of the day changes with the seasons. This could lead to a misalignment of circadian rhythms and environmental light, as well as a misalignment of biological processes like melatonin release and sleep. While this does not seem to explain all cases of seasonal affective disorder, it does provide an explanation for why exposure to very bright light, as is done in bright light therapy, has been found to be effective in treating some cases of the disorder.

Several other hypotheses have been proposed to explain seasonal affective disorder, some of which might be also linked to circadian rhythm disruption. For example, studies have found that some individuals with seasonal affective disorder might have deficiencies in retinal sensitivity to light. Other studies suggest low levels of vitamin D could play a role in some cases, and abnormalities in levels of neurotransmitters like serotonin and norepinephrine have also been implicated.

REFERENCES:

Galima SV, Vogel SR, Kowalski AW. Seasonal Affective Disorder: Common Questions and Answers. Am Fam Physician. 2020 Dec 1;102(11):668-672. PMID: 33252911.

Rohan KJ, Roecklein KA, Haaga DAF. Biological and Psychological Mechanisms of Seasonal Affective Disorder: A Review and Integration. Current Psychiatry Reviews. 2009;5:37-47.

Sohn CH, Lam RW. Update on the biology of seasonal affective disorder. CNS Spectr. 2005 Aug;10(8):635-46; quiz 1-14. doi: 10.1017/s109285290001960x. PMID: 16041295.

Image of trees appearing at the 10-second mark is the work of J. Hageluken, available at: [ Ссылка ]

свернуть