tDCS over the left inferior frontal cortex improves speech production in aphasia

Abstract

In this study, we investigated the combined effect of transcranial direct current stimulation (tDCS) and an intensive Conversational therapy treatment on discourse skills in 12 persons with chronic aphasia. Six short video clips depicting everyday life contexts were prepared. Three videoclips were used to elicit spontaneous conversation during treatment. The remaining three were presented only before and after the therapy. Participants were prompted to talk about the contents of each videoclip while stimulated with tDCS (20 min 1 mA) over the left hemisphere in three conditions: anodic tDCS over the Broca's area, anodic tDCS over the Wernicke's area, and a sham condition. Each experimental condition was performed for 10 consecutive daily sessions with 14 days of intersession interval. After stimulation over Broca's area, the participants produced more Content Units, verbs and sentences than in the remaining two conditions. Importantly, this improvement was still detectable 1 month after the end of treatment and its effects were generalized also to the three videoclips that had been administered at the beginning and at the end of the therapy sessions. In conclusion, anodic tDCS applied over the left Broca's area together with an intensive "Conversational Therapy" treatment improves informative speech in persons with chronic aphasia. We believe that positive tDCS effects may be further extended to other language domains, such as the recovery of speech production.

Keywords: aphasia recovery; language rehabilitation; speech production; stroke; tDCS.

Figure 1

Axial views of color coded probability map of lesion overlap (range 1% purple to 91% white). Individual volume lesions were drawn manually on the re-oriented brain volume transformed into MNI standardized stereotaxic coordinate system using a computational semi-automatic procedure of REGISTER software provided by Brain Imaging Center, Montreal Neurological Institute, McGill University. Averaging the labeled voxels of the individual lesion volumes re-aligned in MNI space generated the probability map revealing the localization of areas of percentage of lesion overlap. Maximal overlap includes the capsula estrema, the claustrum, part of the capsula esterna and the putamen. The inferior frontal gyrus (including the Broca's area) and the superior temporal gyrus (including the Wernicke's area) were similary damaged both having about 45% of lesion overlap.

Figure 2

Localization of the tDCS area (A) and overview of study design (B): one video-clip was used for the anodic Broca's stimulation, one for the anodic Wernicke's stimulation and a third one for the sham Broca's or Wernicke's condition. Each condition was performed in 10 consecutive daily sessions over 3 months, with 14 days of intersession interval, while the subjects underwent the “Conversational Therapy” treatment.

Figure 3

Mean percentage of correct “C-Units” at baseline (T1) and at the end of treatment (T10) for the left anodic Wernicke's, Broca's and sham conditions (^*< 0.01), respectively. Error bars represent standard error of the mean.

Figure 4

Mean percentage of correct verbs at baseline (T1) and at the end of treatment (T10) for the left anodic Wernicke's, Broca's and sham conditions (^*< 0.01), respectively. Error bars represent standard error of the mean.

Figure 5

Mean percentage of correct sentences at baseline (T1) and at the end of treatment (T10) for the left anodic Wernicke's, Broca's and sham conditions (^*< 0.01), respectively. Error bars represent standard error of the mean.

Figure 6

Mean percentage of correct “C-Units”, verbs and sentences during the presentation of the three videos (“Making a coffee”, “The Supermarket” and “The Housekeepers”) presented only at baseline and at the end of treatment in the pre-and post-anodic Broca's, sham and Wernicke's conditions (^*< 0.01), respectively.

Figure 7

Mean percentage of correct C-Units, Verbs and Sentences at the end of treatment (T10) and at the follow-up for the left anodic Wernicke's, Broca's and sham condition. Error bars represent standard error of the mean.