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.
None
MDD diagnosis according to the Diagnostic and Statistical Manual of Mental Disorders, fourth edition (DSM-Ⅳ), first episode or recurrence, confirmed by an experienced psychiatrist using the Mini International Neuropsychiatric Interview.
Age between 18 and 60 years; and gender no-limited;
The severity of MDD symptoms must be ≥14 scores on the HAMD-17;
With CI currently, defined as a total score of <70 on the SC;
Parallel
BLT
DeviceUsing a hybrid white light box with independent intellectual property rights, with an intensity of 10000lux and a main wavelength of 476.4nm
DRL
DeviceUsing a dim red light box as the placebo, with an intensity of \<100lux and a main wavelength of 690.4nm
Symbol Coding (SC)
The Symbol Coding (SC) is a coding paradigm adapted from the Digit Symbol Substitution Test (DSST), both of which use essentially the same method, except in reverse; instead of drawing symbols that match digits, the SC requires to write the matching digit in the blank. The task has been included as a subtest in the Brief Assessment of Cognition in Schizophrenia; in this task, subjects are required to write numerals 1-9 as matches to nonmeaningful symbols on a response sheet for 90 s, as based on a key provided to them, with higher scores reflecting better performance.
Hamilton Depression Rating Scale-17（HDRS-17）
The Hamilton Depression Rating Scale-17 (HAMD-17), developed by Hamilton in 1960, is a widely used clinical rating scale consisting of 17 items that evaluate various depressive symptoms, including mood, suicidal thoughts, sleep disturbances, loss of interest, psychomotor changes, anxiety, gastrointestinal and somatic symptoms, sexual dysfunction, and weight loss. Scored on a scale of 0 to 4 (with some items possibly using a 0 to 2 scale), the total score reflects the severity of depressive symptoms and is used for diagnosing depression, planning tailored treatment, monitoring treatment effectiveness, and conducting research on depression treatment efficacy.
The 20-item Perceived Deficits Questionnaire for Depression（PDQ-D-20）
The Chinese version of the Perceived Deficits Questionnaire for Depression (PDQ-D) has been validated for reliability and validity among patients with depression in China. The PDQ-D comprises 20 items, yielding a total score that ranges from 0 to 80. Higher scores indicate a greater severity of self-perceived cognitive symptoms. Demonstrating good reliability and validity, the questionnaire assesses patients' cognitive function across four dimensions: attention/concentration, prospective memory, retrospective memory, and planning and organization.
The Chinese Brief Cognitive Test（CBCT）
Cognitive function will be also assessed using the CBCT, which has been validated in a large-scale study of schizophrenia patients and has shown good internal consistency and test-retest reliability. Also, additional studies in MDD population provide further evidence of its reliability and validity supporting the robustness of this scale for assessing cognitive function in these clinical groups.
Stroop Color-Word Test (SCWT)
The Stroop Color Word Test (SCWT) was developed by Professor Stroop in 1935 to evaluate subjects' executive functions. The test is a measure of selective attention and the degree of inhibition of irrelevant information in executive functioning. It consists of three main parts: reading words (Stroop-w), color naming (Stroop-c), and color-word interference (Stroop-cw), which require subjects to accurately and quickly read the words or the colors, respectively, as required.
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