Beyond Reading Modulation: Temporo-Parietal tDCS Alters Visuo-Spatial Attention and Motion Perception in Dyslexia

Abstract

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.

Keywords: attention; brain reading networks; children and adolescents; cortical excitability; magnocellular-dorsal pathway; neural noise; neuromodulation.

Figure 1

Coherent dot motion task.

Figure 2

Attentional zooming task.

Figure 3

Coherent dot motion (CDM) accuracy (raw data) for the two stimulation conditions; * represents the significant difference from the chance level of 0.25 and from the threshold of 0.5 of accuracy in LA/RC condition. + represents the significant difference from the chance level of 0.25 in RA/LC condition (panel (A)), p < 0.05 in 75% CDM threshold (panel (B)), and p < 0.05 in slope values (panel (C)), as a function of stimulation condition, obtained from the psychometric curve (logistic) fitted on individual data. Dots represent individual data points.

Figure 4

Reaction times (RTs) in attentional zooming task at 100 ms cue-target SOA (panel (A)), and at 800 ms cue-target SOA (panel (B)) in Left Anodal/Right Cathodal (LA/RC) and Right Anodal/Left Cathodal (RA/LC) conditions. Panel (A): RTs in large cue are significantly slower than small cue in LA/RC condition. Dots represent individual data points. * p < 0.05