Photoperiodicity in Glucose Metabolism in the Human Brain

Photoperiodicity in the human brain function, which is a critical factor for social well-being, has been widely debated. In this study, 432 healthy males underwent fasting-state brain [18F]fluorodeoxyglucose positron emission tomography (PET) scanning twice: first at the baseline and then at the 5-year follow-up. We analyzed the effect of day length on brain glucose uptake separately for the baseline and follow-up studies and examined changes in glucose consumption as a function of the day length deviation for each participant between the repeated PET scans. Glucose uptake in the cuneus was consistently predicted by the day length on the day of scanning and by within-participant day length deviations. This longitudinal large-scale PET study provides a landmark evidence for photoperiodicity in glucose metabolism in the human brain. The cuneus may be an essential part of the visual cortex, translating environmental photoperiodic changes into temporal cues that influence cognitive function and social behavior. Significance statementPhotoperiodicity in the human brain function has been widely debated. The current study provides a landmark evidence in this regard by demonstrating how the photoperiod shapes glucose metabolism in the brain of healthy males, highlighting the crucial role of the cuneus in processing visual information related to photoperiodic changes in the environment. Understanding photoperiodicity in the function of the human brain offers insights into how humans adapt to their environments for social well-being and underscores the potential health implications of changes in the exposure of natural light.