Cognitive Training Combined with Multifocal tDCS over the Reading Network Improves Reading Performance: A Case of Severe Dyslexia

<b>Background:</b> Developmental dyslexia (DD) is the most common form of specific learning disorders (SLDs). From a neurocognitive point of view, dyslexic reading is associated with atypical neurofunctional patterns in the left hemisphere, mainly in the posterior areas linked to lexical access and phonological processing. Nowadays, rehabilitation treatments do not aim to fix the disorder but rather improve adaptive skills. On the other hand, the transcranial direct current stimulation (tDCS) has recently gained popularity in this field. In fact, a few studies have documented enhanced accuracy and speed after the tDCS over the parietal cortex, although the results were mainly limited to non-word reading. <b>Methods:</b> We conducted a single-case study employing an innovative multifocal eight-channel tDCS aimed at increasing the reading network activity in the left hemisphere and inhibiting the contralateral areas. The participant was a 9-year-old boy with a diagnosis of severe mixed-type specific learning disorder. The high-definition multifocal tDCS was administered over key areas of the frontal, temporal, parietal, and occipital lobes (four 3.14 cm² electrodes per hemisphere) in conjunction with tachistoscope training over a span of 10 weeks, with three sessions per week for a total of thirty sessions. Standardized assessments of reading were carried out at the beginning, at the end of the treatment, and at one- and six-month follow-up. <b>Results:</b> The treatment led to a 77% improvement in the accuracy of passage reading and an 83% improvement in the reading of high-frequency short words, with stable results at the 1- and 6-month follow-up. By contrast, in line with the severity of the disorder, there were only slight improvements in the speed parameter. <b>Conclusions:</b> This is the first study to document such remarkable improvements in reading in a case of severe SLD: if confirmed, these promising findings could pave the way for an effective, non-invasive rehabilitation for SLDs using multifocal tDCS. However, future studies are needed to overcome the limitations of single-case studies, such as the lack of control conditions and quantifiable analysis.