Pre-treatment letter fluency performance predicts antidepressant response to transcranial direct current stimulation

•Little is known of inter-individual predictors of response of tDCS for depression.•Pre-treatment neurocognitive predictors from 57 participants were analysed.•Better pre-treatment letter fluency performance predicted response to tDCS.•Inter-individual neurobiological differences appear to mediate tDCS effects.

BackgroundTranscranial direct current stimulation (tDCS) is a promising new treatment for depression, however, clinical trials to-date indicate variable efficacy, thereby raising the need to identify inter-individual predictors of response. In the current study we aimed to investigate pre-treatment neurocognitive performance as a predictor of antidepressant response to tDCS.MethodsData was pooled from five clinical trials, including two randomised controlled trials (RCTs), which investigated the antidepressant effects of anodal tDCS administered to the prefrontal cortex. Data from 57 patients were included in the analysis. Mood was assessed before and after an acute course of treatment using the Montgomery-Åsberg Depression Rating Scale. The following neurocognitive tests were administered prior to treatment: Simple and choice reaction time, the Symbol Digit Modalities Test (SDMT), Rey Auditory Verbal Memory Task (RAVLT), Digit Span, and the Controlled Oral Word Association Test (COWAT).ResultsBetter pre-treatment letter fluency performance measured using the COWAT predicted antidepressant response to tDCS after controlling for confounds.LimitationsSmall sample size and analysis included data from both RCTs and open label studies.ConclusionPre-treatment letter fluency performance, an ability subserved by the left prefrontal cortex, the primary site of stimulation, is a predictor of response for tDCS treatment for depression. This study highlights the importance of inter-individual neurobiological differences in mediating tDCS antidepressant effects.