Non-invasive brain stimulation enhances the effects of melodic intonation therapy

Abstract

Research has suggested that a fronto-temporal network in the right hemisphere may be responsible for mediating melodic intonation therapy's (MIT) positive effects on speech recovery. We investigated the potential for a non-invasive brain stimulation technique, transcranial direct current stimulation (tDCS), to augment the benefits of MIT in patients with non-fluent aphasia by modulating neural activity in the brain during treatment with MIT. The polarity of the current applied to the scalp determines the effects of tDCS on the underlying tissue: anodal-tDCS increases excitability, whereas cathodal tDCS decreases excitability. We applied anodal-tDCS to the posterior inferior frontal gyrus of the right hemisphere, an area that has been shown both to contribute to singing through the mapping of sounds to articulatory actions and to serve as a key region in the process of recovery from aphasia, particularly in patients with large left hemisphere lesions. The stimulation was applied while patients were treated with MIT by a trained therapist. Six patients with moderate to severe non-fluent aphasia underwent three consecutive days of anodal-tDCS + MIT, and an equivalent series of sham-tDCS + MIT. The two treatment series were separated by 1 week, and the order in which the treatments were administered was randomized. Compared to the effects of sham-tDCS + MIT, anodal-tDCS + MIT led to significant improvements in fluency of speech. These results support the hypothesis that, as the brain seeks to reorganize and compensate for damage to left hemisphere language centers, combining anodal-tDCS with MIT may further recovery from post-stroke aphasia by enhancing activity in a right hemisphere sensorimotor network for articulation.

Keywords: Broca’s aphasia; melodic intonation therapy; neurorehabilitation; singing; stroke; tDCS; transcranial direct current stimulation.

Figure 1

Overlay lesion maps. This figure shows a plot of all lesion maps superimposed onto an individual, spatially standaridzed T1-weighted image (NB: images are displayed in neurological orientation: left side of the image is the left hemisphere). The color scale indicates the extent of overlap among patients with green, yellow, and red indicating overlapping voxels of lesion maps of 4, 5, and 6 patients respectively.

Figure 2

The results for six participants with Broca’s aphasia, represented as means ± SEM. Note that a decrease in the total duration signifies an improvement in verbal fluency. Anodal-tDCS led to a significantly greater improvement compared to sham-tDCS.

Figure 3

Data shown separately for each participant. The trend for all but one participant is in the direction of greater improvement in the anodal-tDCS condition compared to sham.