title: Modulating transcallosal and intra-hemispheric brain connectivity with tDCS: Implications for interventions in Aphasia.
abstract: Transcranial direct current stimulation (tDCS) can enhance or diminish cortical excitability levels depending on the polarity of the stimulation. One application of non-invasive brain-stimulation has been to modulate a possible inter-hemispheric disinhibition after a stroke. This disinhibition model has been developed mainly for the upper extremity motor system, but it is not known whether the language/speech-motor system shows a similar inter-hemispheric interaction. We aimed to examine physiological evidence of inter- and intra-hemispheric connectivity changes induced by tDCS of the right inferior frontal gyrus (IFG) using arterial-spin labeling (ASL) MRI.
  
  
  
  Using an MR-compatible DC-Stimulator, we applied anodal stimulation to the right IFG region of nine healthy adults while undergoing non-invasive cerebral blood flow imaging with arterial-spin labeling (ASL) before, during, and after the stimulation. All ASL images were then normalized and timecourses were extracted in regions of interest (ROIs), which were the left and right IFG regions, and the right supramarginal gyrus (SMG) in the inferior parietal lobule. Two additional ROIs (the right occipital lobe and the left fronto-orbital region) were taken as control regions.
  
  
  
  Using regional correlation coefficients as a surrogate marker of connectivity, we could show that inter-hemispheric connectivity (right IFG with left IFG) decreased significantly (p < 0.05; r-scores from 0.67 to 0.53) between baseline and post-stimulation, while the intra-hemispheric connectivity (right IFG with right SMG) increased significantly (p < 0.05;r-scores from 0.74 to 0.81). A 2 × 2 ANOVA found a significant main effect of HEMISPHERE (F(8) = 6.83, p < 0.01) and a significant HEMISPHERE-by-TIME interaction (F(8) = 4.24, p < 0.05) in connectivity changes. The correlation scores did not change significantly in the control region pairs (right IFG with right occipital and right IFG with left fronto-orbital) over time.
  
  
  
  Using an MR-compatible DC stimulator we showed that ASL-MRI can detect tDCS-induced modulation of brain connectivity within and between hemispheres. These findings might affect trial designs focusing on modulating the non-dominant hemisphere to enhance language/speech-motor functions.
authors.affiliation: Department of Neurology, Neuroimaging and Stroke Recovery Laboratory, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA, USA.
authors.forename: Xin
authors.initials: X
authors.lastname: Zheng
authors.affiliation: Division of MR Research, Department of Radiology, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA, USA.
authors.forename: Weiying
authors.initials: W
authors.lastname: Dai
authors.affiliation: Division of MR Research, Department of Radiology, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA, USA.
authors.forename: David C
authors.initials: DC
authors.lastname: Alsop
authors.affiliation: Department of Neurology, Neuroimaging and Stroke Recovery Laboratory, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA, USA.
authors.forename: Gottfried
authors.initials: G
authors.lastname: Schlaug
mesh_terms: D000328:Adult; D001037:Aphasia / Q000534:rehabilitation*; D002540:Cerebral Cortex / Q000000981:diagnostic imaging / Q000502:physiology*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D063132:Connectome / Q000379:methods*; D003337:Corpus Callosum / Q000000981:diagnostic imaging / Q000502:physiology*; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D013113:Spin Labels; D065908:Transcranial Direct Current Stimulation / Q000379:methods*; D055815:Young Adult
chemical_list: D013113:Spin Labels
keywords: Resting state fcMRI; aphasia; arterial spin labeling; brainstimulation; plasticity; rehabilitation; tDCS; transcallosal connectivity