Dyslexia is a neurodevelopmental disorder with an atypical activation of posterior left-hemisphere brain reading networks (i.e., temporo-occipital and temporo-parietal regions) and multiple neuropsychological deficits. Transcranial direct current stimulation (tDCS) is a tool for manipulating neural activity and, in turn, neurocognitive processes. While studies have demonstrated the significant effects of tDCS on reading, neurocognitive changes beyond reading modulation have been poorly investigated. The present study aimed at examining whether tDCS on temporo-parietal regions affected not only reading, but also phonological skills, visuo-spatial working memory, visuo-spatial attention, and motion perception in a polarity-dependent way. In a within-subjects design, ten children and adolescents with dyslexia performed reading and neuropsychological tasks after 20 min of exposure to Left Anodal/Right Cathodal (LA/RC) and Right Anodal/Left Cathodal (RA/LC) tDCS. LA/RC tDCS compared to RA/LC tDCS improved text accuracy, word recognition speed, motion perception, and modified attentional focusing in our group of children and adolescents with dyslexia. Changes in text reading accuracy and word recognition speed—after LA/RC tDCS compared to RA/LC—were related to changes in motion perception and in visuo-spatial working memory, respectively. Our findings demonstrated that reading and domain-general neurocognitive functions in a group of children and adolescents with dyslexia change following tDCS and that they are polarity-dependent.
The possibility to modulate reading in individuals with and without dyslexia using transcranial electrical stimulation, such as tDCS, has been documented in the literature [citations]. Nevertheless, the underlying neurocognitive mechanisms mediating reading changes induced by tDCS are still not well understood.
Our results showed significant changes in text reading errors and word recognition speed as a function of specific electrode polarity. Precisely, when tDCS enhanced left neural excitability while decreasing right neural excitability of the temporo-parietal regions (LA/RC condition), text reading errors reduced, and word recognition speed increased as compared to the inverse polarity (RA/LC condition).
Intriguingly, we found that by enhancing left neural excitability while decreasing right neural excitability of the temporo-parietal regions, not only was word reading modulated but also MD stream functioning and visuo-spatial attentional zooming changed.
Concerning visuo-spatial abilities, correlational analyses showed that better visuo-spatial working memory was related to better word recognition after LA/RC tDCS of temporo-parietal regions compared to RA/LC.
… to the best of our knowledge, this study is the first attempt to clarify the relation between brain modulation and changes in reading, phonological processes, visual attention, and MD stream functioning in dyslexia….
In conclusion, by increasing the neural excitability of the left temporo-parietal areas while reducing the neural excitability of the right temporo-parietal areas in children and adolescents with dyslexia, we found that: (i) word text accuracy and word recognition improved, (ii) visuo-spatial attentional focusing reduced, and (iii) motion perception enhanced.