Evaluation of the combined effect of reading training and tACS on reading-related cognitive abilities in developmental dyslexia: an investigation by neuropsychological assessment

Developmental dyslexia (DD)is a reading disorder whose neural and genetic bases are widely accepted. It occurs despite the presence of cognitive impairment, exposure to a conventional educational setting, access to normal sociocultural opportunities, and the absence of sensory deficits or emotional pathologies. Recent models that integrate three different levels of the disorder, neurobiological, cognitive, and behavioral, have provided hypotheses about the causes of the disease.

Based on these models, which can be grouped into linguistic-phonological and visual-perceptual theories, this study aims to evaluate, in adult participants diagnosed with DD, the effectiveness of a novel neuropsychological treatment that combines tACS stimulation with accelerated reading training to improve the functionality of the magnocellular-dorsal (MD) visual pathway, with potential cascading effects on reading skills and other core deficits of DD. Specifically, this study compares reading skills and deficits in sub-lexical and lexical decoding in participants with DD before and after 12 sessions of the RAP (Reading Acceleration Program) training, with or without transcranial Alternating Current Stimulation (tACS).

Participants, native Italian speakers with a previous diagnosis of DD, were included in a single-blinded randomized clinical trial. The study sample was divided into three groups and two types of training: RAP training and phonological training. The former is an accelerated reading training during which sentences displayed on the screen were removed at a rate proportional to the subject's reading speed. The latter consists of linguistic and phonological exercises, including syllable elision and spoonerism. The three groups were DD1 and DD2, which received RAP training, while DD3 received phonological training sessions. Participants belonging to the experimental group (DD1) received tACS at a frequency of 18 Hz in the beta band and the participants in the otherntwo groups received a placebo(sham) stimulation during their respective training sessions (DD2 and DD3). Before and after the 12 training sessions, all three groups underwent standardized neuropsychological tests.

The preliminary behavioural results showed improved reading time on standardized reading tests for words and pseudowords for all groups (DD1 – DD2 – DD3). Also, letter- reading speed was ameliorated in all groups. Finally, our results showed substantial improvement in working memory skills only in participants undergoing tACS in combination with the RAP training.
Overall, results support the hypothesis that tACS protocols targeting the MD pathway may open up new possibilities for a rehabilitative approach to the disorder. Nevertheless, these are preliminary results of an ongoing study. A larger sample of participants is needed to confirm these results.