Broca's area damage is necessary but not sufficient to induce after-effects of cathodal tDCS on the unaffected hemisphere in post-stroke aphasia.

BACKGROUND: The inter-individual variability of behavioral effects after tDCS applied to the unaffected right hemisphere in stroke may be related to factors such as the lesion location. OBJECTIVE/HYPOTHESIS: We investigated the effect of left Broca's area (BA) damage on picture naming in aphasic patients after cathodal tDCS applied over the right BA. METHODS: We conducted a study using pre-interventional diffusion and resting state functional MRI (rsfMRI) and two cross-over tDCS sessions (TYPE: sham and cathodal) over the right homologous BA in aphasic stroke patients with ischemic lesions involving the left BA (BA+) or other left brain areas (BA-). Picture naming accuracy was assessed after each session. Inter-hemispheric (IH) functional balance was investigated via rsfMRI connectivity maps using the right BA as a seed. Probabilistic tractography was used to study the integrity of language white matter pathways. RESULTS: tDCS had different effects on picture naming accuracy in BA+ and BA- patients (TYPE × GROUP interaction, F(1,19): 4.6, P: 0.04). All BA- patients except one did not respond to tDCS and demonstrated normal IH balance between the right and left BA when compared to healthy subjects. BA+ patients were improved by tDCS in 36% and had decreased level of functional IH balance. Improvement in picture naming after cathodal tDCS was associated with the integrity of the arcuate fasciculus in BA+ patients. CONCLUSIONS: Behavioral effects of cathodal tDCS on the unaffected right hemisphere differ depending on whether BA and the arcuate fasciculus are damaged. Therefore, IH imbalance could be a direct consequence of anatomical lesions.

Connectivity between right inferior frontal gyrus and supplementary motor area predicts after-effects of right frontal cathodal tDCS on picture naming speed.

BACKGROUND: Cathodal transcranial direct current stimulation (tDCS) of the right frontal cortex improves language abilities in post-stroke aphasic patients. Yet little is known about the effects of right frontal cathodal tDCS on normal language function. OBJECTIVE/HYPOTHESIS: To explore the cathodal tDCS effects of the right-hemispheric homologue of Broca's area on picture naming in healthy individuals. We hypothesized that cathodal tDCS improves picture naming and that this effect is determined by the anatomical and functional connectivity of the targeted region. METHODS: Cathodal and sham tDCS were applied to the right inferior frontal gyrus in 24 healthy subjects before a picture-naming task. All participants were studied with magnetic resonance imaging at pre-interventional baseline. Probabilistic tractography and dynamic causal modeling of functional brain activity during a word repetition task were applied to characterize anatomical and functional connectivity. RESULTS: Subjects named pictures faster after cathodal relative to sham tDCS. The accelerating effect of tDCS was explained by a reduced frequency of very slow responses. tDCS-induced acceleration of picture naming correlated with larger volumes of the tract connecting the right Broca's area and the supplementary motor area (SMA) and greater functional coupling from the right SMA to the right Broca's area. CONCLUSIONS: The results support the notion that the after-effects of tDCS on brain function are at least in part determined by the anatomical and functional connectivity of the targeted region.

The Aphasia Rapid Test: an NIHSS-like aphasia test.

The Aphasia Rapid Test (ART) is a 26-point scale developed as a bedside assessment to rate aphasia severity in acute stroke patients in <3 min. We tested its inter-rater reproducibility, its sensitivity to detect changes from Day 1 to Day 8, and the predictive value of D8 ART scores on the 3-month aphasia outcome assessed with the Aphasia Handicap Score (AHS), a 0-5 "Rankin-like" score for aphasic disability. The reproducibility was tested in 91 aphasic patients within one week of stroke onset. The inter-rater concordance coefficient was 0.99 and the weighted Kappa value (κw) was 0.93. The sensitivity was tested in 70 aphasic patients by measuring changes in ART values between D1 and D8. Improvement occurred in 46 patients (66 %) and aggravation in three patients (4 %). In these patients, a logistic regression analysis showed that D8 ART was the only significant predictor of good (AHS 0-2) or poor (AHS 4-5) outcome. The ROC curves analyzes showed areas under the curve above 0.9 for good and poor outcome and revealed D8 ART best cut-off values of <12 for good and >21 for poor outcome, with more than 90 % sensitivity and 80 % specificity. The ART is a simple, rapid and reproducible language task, useful in monitoring early aphasic changes in acute stroke patients and highly predictive of the 3-month verbal communication outcome. It should be easy to adapt to other languages.