Verbal Fluency in Parkinson’s disease: neuroanatomical correlates and functional networks modulated by noninvasive brain stimulation

Background: Verbal fluency relies on the coordinated activity between left frontal and temporal areas.Patients with Parkinson’s disease (PD) present phonemic and semantic fluency deficits. Recent studiessuggest that transcranial direct current stimulation (tDCS) enhances adaptative patterns of brain activitybetween functionally connected areas.Objective: The aimof this studywas to assess thedifferences in the effects inducedby tDCS applied to frontaland temporo-parietal areas on phonemic and semantic fluency functional networks in patients with PD.Method: Sixteen patients were randomized to receive tDCS to left dorsolateral prefrontal cortex (DLPFC)and left temporo-parietal cortex (TPC) in a counterbalanced order. Immediately following stimulation,patients underwent a verbal fluency paradigm inside a fMRI scanner. Changes induced by tDCS inactivation and deactivation task-related pattern networks were studied using free-model independentcomponent analyses (ICA).Results: Functional connectivity in verbal fluency and deactivation task-related networks was signifi-cantly more enhanced by tDCS to DLPFC than to TPC. In addition, DLPFC tDCS increased performance onthe phonemic fluency task, after adjusting for baseline phonemic performance.Conclusions: These findings provide evidence that tDCS to specific brain regions induces changes in largescale functional networks that underlay behavioural effects, and suggest that tDCS might be useful toenhance phonemic fluency in PD.2012 Elsevier Inc. All rights reserved.