title: Task-dependent and polarity-specific effects of prefrontal transcranial direct current stimulation on cortical activation during word fluency.
abstract: Targeted modulation of cortical functions by non-invasive brain stimulation is widely used for the investigation of the neurophysiological signatures of executive functions and put forward as a potential specific treatment for its disorders. To further investigate the underlying mechanisms, we performed two experiments involving 46 subjects that performed a semantic and a phonological verbal fluency task (VFT) as well as a simple speech-production task after application of 1mA anodal or cathodal transcranial direct current stimulation (tDCS) to the left inferior frontal gyrus (IFG). Brain activation was measured by functional near-infrared spectroscopy (fNIRS) during task performance. Neither preceding anodal nor cathodal tDCS was found to modulate VFT performance of either difficulty. However, preconditioning with anodal tDCS increased brain activity during the VFT whereas a trendwise decrease of activation was found after cathodal stimulation. Notably, this difference was not found with simple speech production. These findings support the notion of a polarity-specific malleability of neuronal network activity underlying speech production by tDCS. Most importantly, the task-specificity of the modulatory effect observed after the end of stimulation demonstrates lasting neurophysiological effects of tDCS that are reflected in modifications of cortical excitability by challenging cognitive tasks.
authors.affiliation: Department of Psychiatry and Psychotherapy, University Hospital Tuebingen, Calwerstr. 14, 72076 Tuebingen, Germany. Electronic address: Ann-Christine.Ehlis@med.uni-tuebingen.de.
authors.forename: Ann-Christine
authors.initials: AC
authors.lastname: Ehlis
authors.affiliation: Department of Psychiatry and Psychotherapy, University Hospital Tuebingen, Calwerstr. 14, 72076 Tuebingen, Germany.
authors.forename: Florian B
authors.initials: FB
authors.lastname: Haeussinger
authors.affiliation: Department of Psychiatry and Psychotherapy, University Hospital Tuebingen, Calwerstr. 14, 72076 Tuebingen, Germany.
authors.forename: Alex
authors.initials: A
authors.lastname: Gastel
authors.affiliation: Department of Psychiatry and Psychotherapy, University Hospital Tuebingen, Calwerstr. 14, 72076 Tuebingen, Germany.
authors.forename: Andreas J
authors.initials: AJ
authors.lastname: Fallgatter
authors.affiliation: Department of Psychiatry and Psychotherapy, University Hospital Tuebingen, Calwerstr. 14, 72076 Tuebingen, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Plewnia
mesh_terms: D000328:Adult; D001931:Brain Mapping / Q000379:methods; D000071080:Cortical Excitability / Q000502:physiology*; D005260:Female; D006801:Humans; D017774:Long-Term Potentiation / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D009415:Nerve Net / Q000502:physiology; D009473:Neuronal Plasticity / Q000502:physiology*; D017397:Prefrontal Cortex / Q000502:physiology*; D012660:Semantics; D013060:Speech / Q000502:physiology*; D013647:Task Performance and Analysis; D065908:Transcranial Direct Current Stimulation / Q000379:methods*; D055815:Young Adult
keywords: Broca's area; Functional near-infrared spectroscopy (fNIRS); Prefrontal cortex (PFC); Transcranial direct current stimulation (tDCS); Verbal fluency test (VFT)