Effects of seasonal factors on brain function: Systematic review and future perspectives

Summary: The empirical evidence for the effects of changing seasons on humans and other species has long been a subject of public and scientific curiosity. However, supporting evidence is predominantly behavioral, warranting further quantitative/mechanistic validation. Three putative mechanisms proposed here include (1) variability in photoperiod and temperature, (2) gravitational effects from varying Earth-celestial body distances, including lunar phases and eclipses, and (3) changes in geomagnetism. This systematic review (PubMed, Web of Science, and Scopus; until September’24) aims to identify studies on the effects of seasonality, gravity, and geomagnetism on brain function, establishing a baseline for the proposed hypotheses. Distinct search queries were tailored to capture the relevant literature. Behavioral and observational data support the hypotheses, with limited EEG/MRI evidence indicating potential neural correlates, although most research is cross-sectional and preliminary. Future work should employ well-powered, longitudinal, and hypothesis-driven designs to clarify the observed effects, thereby confirming or challenging competing views.