Efficacy of non-invasive brain stimulation on theory of mind and emotion processing in neuropsychiatric disorders: A systematic review and meta-analysis

Social cognitive impairments, including emotion processing (EP) and theory of mind (ToM), have been considered as transdiagnostic features across neuropsychiatric disorders, substantially affecting social functioning. While no definitive treatment exists for these deficits, non-invasive brain stimulation (NIBS) has emerged as a promising option but a comprehensive quantitative review was lacking. This systematic review and meta-analysis were conducted to evaluate the effects of transcranial direct current stimulation (tDCS) and transcranial magnetic stimulation (TMS) on EP and ToM deficits across diverse neuropsychiatric disorders. Following PRISMA guidelines, eligible randomized sham-controlled trials were systematically searched. Hedges’ g was utilized to quantify effect sizes for pretest-posttest-control group designs. A total of 36 studies comprising 1486 participants were included. Meta-analyses revealed a modest yet significant effect of TMS on EP compared to sham (g = 0.295 [95 % CI, 0.065–0.524], p = 0.012), while no significant effects were found for tDCS on EP or ToM, nor of TMS on ToM. Notably, more prominent effects were observed with TMS targeting the left dorsolateral prefrontal cortex (dlPFC) and utilizing facial emotion recognition tasks. However, the high heterogeneity and limited long-term follow-up data call for careful consideration of the durability and consistency of these effects. Potential publication bias was also observed for tDCS on EP. Overall, TMS shows promise for mitigating social cognitive impairments, primarily in EP, but further rigorous investigation is needed to validate its clinical efficacy and long-term benefit. Future research should incorporate large-scale longitudinal studies with neuroimaging and real-world social functioning assessments across disorders.