2018.02.28 Dr. Mehdi Bakhtiar

Research Assistant Professor

Department of Chinese and Bilingual Studies

The Hong Kong Polytechnic University

The effect of right hemisphere stimulation on language recovery in left-brain damage patients with chronic aphasia

Over the past decades, the application of transcranial direct current stimulation (tDCS), has received an increasing attention as a potential complement to traditional behavioral therapy for stroke patients with Aphasia. However, different tDCS parameters were employed including the stimulation of right versus left hemisphere and application of anodal (excitatory) versus cathodal (inhibitory) stimulations. There are two opposing hypotheses, namely the interference hypothesis and the compensatory hypothesis regarding the role of right hemisphere (RH) activation in language recovery following the brain damage in the left hemisphere. The present preliminary study aims to investigate the effect anodal tDCS of RH inferior frontal gyrus in left-hemispheric damaged patients with chronic aphasia to a) examine the compensatory versus interference role of RH in language recovery, and b) to confirm that the application of tDCS for language intervention does not induce any adverse effects on other cognitive functions.

Four right-handed native Cantonese-speaking patients with aphasia following the left-hemisphere lesions participated in a randomized, double-blind, sham-controlled crossover experiment. The participants received five consecutive days of 20-minutes anodal tDCS (one mA) and five consecutive days of 20-minutes sham tDCS (with randomized order), together with 40 minutes of online naming therapy delivered by a speech therapist. The patients’ speech, language and, cognitive functioning was tested before and after the anodal and sham conditions using a picture naming task and other standardized language and cognitive assessment batteries.

In general, the patients showed more improvement in terms of their naming abilities following sham condition versus the anodal tDCS of RH, though the difference was statistically significant in one patient. No adverse effects of tDCS application were found on the cognitive functions as well.

The results of the current study suggest that the excitatory stimulation of the right inferior frontal gyrus may exert an inhibitory effect on word learning in chronic patients with aphasia, which could be interpreted more in the favor of the interference hypothesis. However, the results need to be supported by the further group studies using different paradigms to verify the role of RH activation on language recovery in patients with aphasia across the different post-stroke stages.