Decreased functional connectivity within the salience network after two-week morning bright light exposure in individuals with sleep disturbances: a preliminary randomized controlled trial

Background: Bright light (BL) exposure is a safe non-pharmacological intervention for sleep disturbances. However, the functional brain correlates underlying the effects of bright light exposure need to be further clarified. As alterations in the salience network were reported in individuals with sleep disturbances, we have investigated whether bright light exposure may improve sleep quality by altering functional connectivity in this network. Methods: In the current study, 30 individuals with sleep disturbances were randomly assigned to one of the two interventions for two weeks: (1) 1 h of bright light (10,000 lux) exposure (BL-exposed group) and (2) 1 h of dim light (<300 lux) exposure (DL-exposed group). Sleep characteristics and functional connectivity in the salience network were assessed by sleep diary and resting-state functional magnetic resonance imaging, respectively, as outcome measures at before and after the intervention. Results: After two weeks of the intervention, the BL-exposed group showed greater improvement with respect to sleep efficiency (t = 2.27, p = 0.03) and sleep latency (t = −2.40, p = 0.03) as compared to the DL-exposed group. In addition, functional connectivity decreased in the cluster that encompasses the right anterior insular and the frontal opercular regions in the salience network (uncorrected p < 0.001, cluster size>100 mm³) in the BL-exposed group. Decreased functional connectivity in the cluster was associated with decreased sleep latency in the BL-exposed group (β = 0.54, p = 0.01). Conclusions: Our results suggest that bright light exposure may improve sleep quality in individuals with sleep disturbances by modulating functional connectivity in the salience network. Clinical trial registration: https://cris.nih.go.kr/cris; KCT0002607.