The effect of non-invasive brain stimulation in reducing anhedonia and apathy in major depressive disorder and schizophrenia: A meta-analysis

Abstract

Background: Anhedonia and apathy are core symptoms of Major Depressive Disorder (MDD) and schizophrenia, and respectively refer to deficit in reward processing and motivation. Emerging evidence indicates noninvasive brain stimulation (NIBS) such as transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS) may be effective in treating anhedonia and apathy. Objective: To quantitatively synthesize existing literature on the efficacy of TMS and tDCS in alleviating anhedonia and apathy among individuals with MDD and schizophrenia. Methods: This meta-analysis synthesized findings from 22 previous studies including adults with MDD and schizophrenia (total N = 1258, female% = 43.73 %, age = 37.33 ± 8.35 years, PROSPERO registration no. CRD42023426223). A multilevel random-effect model was adopted to compute pooled effect size and heterogeneity across studies. Results: NIBS shows an overall significant effect in reducing anhedonia and apathy among individuals with MDD and schizophrenia, which is more robust for unilateral excitatory stimulation over the left DLPFC and for RCT studies. While TMS shows no specific effect in reducing anhedonia, it shows a significant effect in decreasing apathy, with both effects dependent on the outcome measurement method. Limited evidence shows significant overall effect of tDCS in reducing anhedonia and apathy, but its specific effect on apathy is inconclusive. Conclusions: NIBS methods show overall modest effects in reducing anhedonia and apathy in MDD and schizophrenia, but the heterogeneity is high that may result from limited study number and methodological variations such as stimulation location. More studies need to be conducted particularly for tDCS intervention, and using task and specific measures of anhedonia and apathy.