Increasing the uptake of 18F-fluorodeoxyglucose in the left hippocampus after 4 weeks of bright light exposure in healthy participants: A randomized controlled study

Bright light therapy (BLT) has been used to treat seasonal affective disorders, depression, and bipolar depression; however, the precise mechanism remains unclear. Neurogenesis in the human brain occurs in the hippocampal dentate gyrus (DG). Stress-induced structural remodeling in the adult hippocampus provides a cellular basis for understanding the impairment of neural plasticity in the human hippocampus in depression. Antidepressant treatment both restores neurogenesis in the hippocampus and serves to normalize behavior in depression animal models, suggesting that deficits in neurogenesis of hippocampus can act as a potential target for depression therapies. Thus, we hypothesized that bright light (BL) may induce neurogenesis in the human hippocampus, especially in the DG. We previously reported that 5-day BL significantly increased the uptake of F-fluorodeoxyglucose (FDG) in the right olfactory cortex, however significant metabolic change did not detect in the hippocampus. The limitations of our previous study are the lack of the direct evidence for neurogenesis and a short duration of BL. Therefore, we previously conducted a randomized controlled trial that revealed a 4-week period of BL in healthy participants resulted in an increase in the volume of the left hippocampal DG-head. This research letter used and analyzed the data of F-FDG positron emission tomography (PET), which was performed simultaneously with magnetic resonance imaging in the previous study.