Efficacy of transcranial direct current stimulation for treating anhedonia in patients with depression: A randomized, double-blind, sham-controlled clinical trial

Background: Anhedonia, the core symptom of major depressive disorder (MDD), is highly prevalent in patients with depression. Anhedonia is associated with low efficacy of drug treatment, high suicide rates, and poor social function. Transcranial direct current stimulation (tDCS) is a non-invasive neuromodulation technology that uses constant, low-intensity direct current to treat MDD by regulating cortical activity and neuronal excitability. However, little is known about the efficacy of tDCS for treating anhedonia in patients with depression, and even the existing results of clinical trials are conflicting. In addition, there is no consensus on what brain regions should be targeted by tDCS during the treatment of anhedonia in patients with depression.

Objective: This study aimed to evaluate the efficacy and safety of tDCS over the left dorsolateral prefrontal cortex (DLPFC) and right orbitofrontal cortex (OFC) in the improvement of anhedonia in patients with depression and finally identified suitable brain regions to be stimulated during treatment.

Methods: This randomized, double-blind, sham-controlled clinical trial recruited 70 patients with anhedonia and depressive episodes. Patients were randomly assigned to three groups according to the stimulation site: right orbitofrontal cortex (OFC), left dorsolateral prefrontal cortex (DLPFC), and sham stimulation. Each group received twelve 20-min interventions (ten as primary treatment and two for consolidation). The primary outcome was a decrease in Snaith-Hamilton Pleasure Scale (SHAPS) scores after primary treatment. Evaluations were performed at baseline, post-treatment, and 8-week follow-up.

Results: The depression mood of the three groups of patients at each time point was better than the baseline, but there was no significant difference in the efficacy between the groups (p>0.05). On the basis of the improvement of depression, this study found that tDCS of the DLPFC significantly improved anhedonia (p = 0.028) after primary treatment (2 weeks), and tDCS of the DLPFC and OFC significantly improved social functioning (p = 0.005) at 8-week follow-up.

Limitations: The sample size of this study was small, with only about 23/24 patients in each group completing the intervention assessments; due to the impact of the COVID-19 epidemic, data analysis was limited by the lack of patients during the follow-up period.

Conclusions: tDCS of the DLPFC significantly improves anhedonia in depressed patients and is thus a potential adjuvant therapy for anhedonia in these patients.