Effects of transcranial direct current stimulation on action-verb processing in patients with Parkinson's disease

Abstract

The aim of this study is to investigate the effects of transcranial direct current stimulation (tDCS) combined with cognitive training (CT) on action-verb processing in patients with Parkinson’s disease (PD). A pilot, randomized double-blind controlled, clinical trial was conducted with 30 patients with PD assigned to two groups: (I) active anodal tDCS over M1 and IFG plus CT (experimental group), or (II) sham tDCS plus CT (control group). All PD participants who met UK Parkinson Disease Society Brain Bank criteria were evaluated using part III of the Unified Parkinson’s Disease Rating Scale (UPDRS) and Hoehn and Yahr’s stages I or II. The patients were undergoing antiparkinsonian therapy and were evaluated during the “on” phase of their medication, and were evaluated with the Addenbrooke Cognitive Examination- revised and the INECO Frontal Screening. The primary outcome (action-verb processing) was assessed by time-picture word paradigm. Motor impairment, bradykinesia and balance, were analyzed as secondary outcomes. We found that active vs. sham tDCS led to an increase in the rate of correct responses in the time-picture word paradigm. This improvement were more notable in verbs with high manipulability versus verbs with low manipulability. Our results showed that active stimulation of left IFG and M1 resulted in improvements in action-verb processing. Thus, our findings encourage further investigation exploring tDCS as an adjuvant therapy for cognitive treatment in PD.