Improved naming in patients with Broca's aphasia with tDCS

Abstract

Background: Language impairment (aphasia) is a common neurological deficit after strokes. For individuals with chronic aphasia (beyond 6 months after the stroke), language improvements with speech therapy (ST) are often limited. Transcranial direct current stimulation (tDCS) is a promising approach to complement language recovery but interindividual variability in treatment response is common after tDCS, suggesting a possible relationship between tDCS and type of linguistic impairment (aphasia type).

Methods: This current study is a subgroup analysis of a randomised controlled phase II futility design clinical trial on tDCS in chronic post-stroke aphasia. All participants received ST coupled with tDCS (n=31) vs sham tDCS (n=39). Confrontation naming was tested at baseline, and 1, 4, and 24 weeks post-treatment.

Results: Broca's aphasia was associated with maximal adjunctive benefit of tDCS, with an average improvement of 10 additional named items with tDCS+ST compared with ST alone at 4 weeks post-treatment. In comparison, tDCS was not associated with significant benefits for other aphasia types F(1)=4.23, p=0.04. Among participants with Broca's aphasia, preservation of the perilesional posterior inferior temporal cortex was associated with higher treatment benefit (R=0.35, p=0.03).

Conclusions: These results indicate that adjuvant tDCS can enhance ST to treat naming in Broca's aphasia, and this may guide intervention approaches in future studies.

Keywords: APHASIA; ELECTRICAL STIMULATION; SPEECH; STROKE.

Figure 1

Figure 1A – Top row: lesion overlaps for each patient group, with the colorbars indicating the number patients with lesions at each voxel. The error bars correspond to the standard error of the mean (SEM - standard deviation of the sampling distribution). Bottom row: the subplots demonstrate treatment outcomes (gains in the number of correct named items in the PNT) at each time point post-treatment (1-, 4- and 24- weeks) for the corresponding patient groups. Figure 1B – The box and whisker plots demonstrate the PNT gains at 4 weeks post-treatment for participants with Broca’s aphasia. This is an expanded view of the data in the center error bar plot in 1A. Based on the PNT gains at 4 weeks post-treatment, the line graph demonstrates the number-needed-to-treat (NNT) (y axis) across a range of PNT gains (x axis) for A-tDCS vs S-tDCS. Note that for a PNT= 9 points, the NNT is 1.9 for A-tDCS (speech therapy with tDCS) and 4.2 for S-tDCS (speech therapy alone). Figure 1C – The scatter plot demonstrates that a lower percentage of lesion (higher preservation) of the Posterior Inferior Temporal Gyrus (PSIG) was associated with higher treatment-related naming improvement among patients who received A-tDCS, controlling for total lesion size. The size of each data point in the scatter plot is proportional to the total lesion volume. The PSIG region of interest is shown in purple, and it is also identified by the red crosshair. The lesion overlay across all patients is shown in “jet” color scheme and the cortical projection of the electrode centers-of-mass across all participants is shown in blue in the lower brain rendering. At a group level, the PSIG was located in the perilesional temporal region with high anode electrode coverage.