Transcranial Direct Current Stimulation over the Right Inferior Parietal Cortex Reduces Transposition Errors in a Syllabic Reordering Task

Vanessa Costa,Filippo Brighina,Chiara Finocchiaro,Giuseppe Giglia,Brigida Fierro,Simona Talamanca,Giuseppe Cosentino

doi:10.3390/sym13112077

Abstract

Evidence derived from functional imaging and brain-lesion studies has shown a strong left lateralization for language, and a complementary right hemisphere dominance for visuospatial abilities. Nevertheless, the symmetrical functional division of the two hemispheres gives no reason for the complexity of the cognitive operations involved in carrying out a linguistic task. In fact, a growing number of neuroimaging and neurostimulation studies suggest a possible right hemisphere involvement in language processing. The objective of this work was to verify the contribution of the left and right parietal areas in a phonological task. We applied anodal transcranial direct current stimulation (tDCS) to the right or left inferior parietal lobe, during a syllabic reordering task. After having learnt a combination of images of real objects and trisyllabic pseudowords with a simple consonant–vowel (CV) syllabic structure (e.g., tu-ru-cu), participants were shown the same images paired to two different pseudowords: one correct but with transposed syllables, and one alternative, never before seen. The participant’s task was to orally produce the chosen pseudoword, after having rearranged the order of its syllables. Two types of error were considered: transposition (correct pseudoword but incorrectly reordered) and identity (incorrect pseudoword). The results showed that right anodal stimulation significantly reduced the number of transposition errors, whereas left anodal stimulation significantly reduced the number of identity errors. These results suggested that both left and right inferior parietal areas were differentially involved in a syllabic reordering task, and, crucially, they demonstrated that visuospatial processes served by the right inferior parietal area could be competent for establishing the correct syllabic order within a word.

Highlights

IntroductionRaboyeau et al [12] reported PET activation of the right inferior frontal areas in healthy subjects, who had to learn and retrieve phonological representations of foreign words
The aim of this work was to verify the effect of anodal transcranial direct current stimulation (tDCS) when applied to the right or left inferior parietal cortex in a syllabic reordering task
The results showed that transposition and identity errors significantly decreased during respectively right and left anodal tDCS

Summary

Introduction

Raboyeau et al [12] reported PET activation of the right inferior frontal areas in healthy subjects, who had to learn and retrieve phonological representations of foreign words. Hartwigsen and collaborators [17] used high-frequency repetitive transcranial magnetic stimulation (rTMS) over the posterior inferior frontal gyrus (pIFG); participants had to decide if the presented word had two or three syllables. They found that both the left and right pIFG contributed to the improvement of accuracy and reaction times in visual and auditory phonological decision tasks, and they concluded that the right pIFG is necessary for accurate and efficient phonological decisions in the healthy brain. The same researchers [18] reported an increase in the number of errors and reaction times during a syllabic decision task using interfering rTMS on both left and right supramarginal gyri

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