Efficacy of Bright Light Therapy on Cognitive Impairment in Major Depressive Disorder and Its Neuroimaging Mechanisms: Protocol for a Randomised Controlled Trial

This study aims to validate the therapeutic efficacy and safety of bright light therapy (BLT) in ameliorating cognitive impairment (CI) in major depressive disorder (MDD), characterize the functional and structural features of the hippocampus (HPC)-dorsolateral prefrontal cortex (dlPFC) neural circuitry in MDD participants with CI and examine the mediating effect of the HPC-dlPFC neural circuit on CI induced by BLT treatment in MDD participants. MDD participants will be required to only receive selective serotonin reuptake inhibitors (SSRIs) as monotherapy for at least four weeks, or medication-free status before enrollment. Eligible participants will be randomly assigned to the experimental group and the control group. The experimental group will receive the intervention of BLT, and the control group will receive the intervention of dim red light (DRL). The intervention will last for four weeks, 6 days per week, with 40 minutes each day between 7 am and 10 am. The MDD participants will be followed once in the end of each week during the 4-week intervention and in the end of the 4th week after intervention. Demographic information will be collected at baseline; cognitive function will be evaluated at baseline, weeks 2, 4, and 8 after intervention beginning; and other symptoms such as depression, anxiety and sleep were assessed at baseline, weeks 1, 2, 3, 4, and 8 after intervention beginning. Moreover, structural and functional MRI scans will be made at baseline and post-intervention. During the intervention, MDD participants will be required to keep a record of daily light exposure duration and complete the daily sleep diary as well.