Science

Hirofumi Hirakawa, Takeshi Terao, Koji Hatano, Masanao Shirahama, Tsuyoshi Kugimiya, Kentaro Kohno, Hiroyuki Matsuta, Tsuyoshi Shimomura and Minoru Fujiki

Bright light exposure (BL) induces neurogenesis in the rat hippocampal dentate gyrus (DG). We had previously conducted a randomized controlled trial (RCT) in which a 4-week period of BL in healthy participants resulted in increased volume of the left DG- head. This study aimed to investigate the effects of BL on the DG in patients with mood disorders. A 4-week RCT was conducted in which patients with mood disorders were randomly assigned to either a BL group (10,000 lx) or dim light exposure group (DL group; 50 lx). All patients underwent clinical assessment and magnetic resonance imaging at baseline and after the intervention. The study registration number is UMIN000019220. Our final sample included 24 patients (BL group, n = 12; DL group, n = 12). A significant effect of time and group was detected in the volumes of the left DG-head (F (1, 22) = 11.6, partial η2 = 0.35, p = 0.003) and left DG-total (left DG-total = left DG-head + left DG-body; [F (1, 22) = 6.5, partial η2 = 0.23, p = 0.02]). Additionally, the BL group demonstrated a significant increase in the volume of the left DG-head (95% CI: −5.4 to −1.6, d = 1.2, p = 0.002) and left DG- total (95% CI: −6.3 to −1.5, d = 1.06, p = 0.005) as well as a positive correlation between the percentage change in the volume of the left DG-total and the percentage change in the scores of the mood visual analog scale (r = 0.58, p = 0.04). In conclusion, our study results suggest that compared to DL, BL leads to a significantly greater increase in the left DG volume in patients with mood disorders. This increase in the left DG volume may be associated with mood improvement in the patients.