Using multisession tDCS stimulation as an early intervention on memory bias processing in subthreshold depression

Transcranial direct current stimulation (tDCS) as an intervention tool has gained promising results in major depression disorder. However, studies related to subthreshold depression's (SD) cognitive deficits and neuromodulation approaches for the treatment of SD are still rare. We adopted Beck's cognitive model of depression and tested the tDCS stimulation effects on attentional and memory deficits on SD. First, this was a single‐blinded, randomized, sham‐controlled clinical trial to determine a 13‐day tDCS modulation effect on 49 SD (27: Stimulation; 22: Sham) and 17 healthy controls. Second, the intervention effects of the consecutive and single‐session tDCS were compared. Furthermore, the attentional and memory biases were explored in SD. Anodal tDCS was administrated over left dorsolateral prefrontal cortex for 13 consecutive days. Attentional and memory bias were assessed through a modified Sternberg task and a dot‐probe task on the 1st, 2nd, and 15th day while their EEG was being recorded. After the 13‐day tDCS stimulation (not after single‐session stimulation), we found reduced memory bias (Stimulation vs. Sham, p = .02, r2 = .09) and decreased mid‐frontal alpha power (p .15). Finally, reduced depressive symptoms (e.g., BDI score) were found for both groups. The criteria of SD varied across studies; the efficacy of this protocol should be tested in elderly patients. Our study suggests memory bias of SD can be modulated by the multisession tDCS and alpha power could serve as a neural index for intervention. The effectiveness of different treatments remains inconclusive in subthreshold depression. The effect of cognitive interventions, such as transcranial direct current stimulation, in subthreshold depression (SD) is unclear. After 13 successive days of stimulation over the dorsolateral prefrontal cortex (F3), we found reduced memory bias and alpha power but no attentional biases, suggesting memory bias of SD can be modulated by multisession tDCS and alpha power can serve as a neural index for intervention.