Seasonal Affective Disorder Research Roundup: December 29, 2023


What is new in research on seasonal affective disorder?

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In this Research Roundup, we explore new studies on seasonal affective disorder and its effects on specific patient populations, sleep patterns, and more.

Bright Light Therapy for SAD
This study investigated the potential neural mechanisms underlying the therapeutic effects of bright light therapy (BLT) in seasonal affective disorder (SAD) using diurnal rodent models. For the neuroinflammatory markers, BLT decreased TNF-α in the basolateral amygdala (BLA) of females and increased CD11b in the medial prefrontal cortex (mPFC) and IL6 in the BLA in males. As for neuroplasticity markers, BLT reduced brain-derived neurotrophic factor (BDNF) in the CA1 and tropomyosin receptor kinase B (TrkB) in all 3 brain regions in females but increased BDNF in the BLA and CA1 in males.

The results suggest that BLT may contribute to its therapeutic effects on sleep, mood, and cognition through mechanisms involving modulation of neuroinflammation and neuroplasticity in specific brain regions, with variations observed between male and female participants.


Costello A, Linning-Duffy K, Vandenbrook C, et al. Effects of bright light therapy on neuroinflammatory and neuroplasticity markers in a diurnal rodent model of seasonal affective disorderAnn Med. 2023;55(2):2249015.

SAD, Hypersomnolence, and Sleep Patterns
In this study on SAD and hypersomnolence, sleep patterns were examined across seasons using various measurements in individuals with SAD and nonseasonal controls. Although individuals with SAD reported longer sleep durations and increased daytime sleepiness in winter compared to summer, total sleep time did not significantly differ between seasons or groups. The study highlights that hypersomnolence in SAD is not solely characterized by extended sleep duration, emphasizing the need for a comprehensive evaluation of sleep disruptions in mood disorders before considering sleep interventions.

“Despite a winter increase in total sleep time and year-round elevated daytime sleepiness, the average total sleep time (7 h) suggest hypersomnolence is a poor characterization of SAD,” the investigators concluded. “Importantly, self-reported hypersomnia captures multiple sleep disruptions, not solely lengthened sleep duration. We recommend using a multimodal assessment of hypersomnolence in mood disorders prior to sleep intervention.”


Wescott DL, Franzen PL, Hasler BP, et al. Elusive hypersomnolence in seasonal affective disorder: actigraphic and self-reported sleep in and out of depressive episodesPsychol Med. 2023;53(4):1313-1322.

Prevalence of SAD in the Southern Hemisphere
This study aimed to establish an evidence base for SAD in Australia, given the limited exploration of SAD in the southern hemisphere. The investigators identified 13 studies that investigated the presence, contributing factors, autonomic activity, treatment, and validity of assessment tools for SAD, revealing an association between changes in mood and behavior with seasonal occurrence, varying by location.

“Ascertaining information on the prevalence and correlates of SAD in the southern hemisphere, particularly in high-risk locations, could contribute to clinical literacy into the syndrome, support management practices, and promote the early identification and treatment of the disorder,” the investigators concluded.


Nevarez-Flores AG, Bostock ECS, Neil AL. The underexplored presence of seasonal affective disorder in the southern hemisphere: a narrative review of the Australian literatureJ Psychiatr Res. 2023;162:170-179.

Note: This Research Roundup was prepared with the assistance of ChatGPT.

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