Several studies have shown that the modulation of cortical activity through
transcranial direct current stimulation (
tDCS) enhances naming performance in persons with
aphasia. In this study, we investigated the potential effects of
tDCS in improving spontaneous speech and the ability to use connective words to establish cohesion among adjacent utterances in a group of eight participants with chronic non
fluent aphasia. They were administered five short videoclips representing everyday life contexts and two picture description tasks. Three videoclips were used to elicit spontaneous conversation during the treatment, while the remaining tasks were presented to the patients only before and after the
therapy. Patients were required to talk about each videoclip, with the help of a therapist, while they were treated with
tDCS (20 min, 1 mA) over the left hemisphere in three different 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 ten consecutive daily sessions with 14 days of intersession interval. Only after Broca's stimulation, patients showed a greater improvement in producing words that enhanced the cohesion of their speech samples (i.e., pronouns, ellipses, word repetitions, conjunctions). Beneficial effects of the stimulation were generalized also to contexts presented to the patients at the beginning and at the end of the
therapy sessions. Our data further confirm the key role of the left inferior frontal gyrus in binding words into a coherent speech. We believe that positive
tDCS effects may be further extended to different linguistic domains, useful to promote language recovery.