Effects of online tDCS and hf-tRNS on reading performance in children and adolescents with developmental dyslexia: a study protocol for a within-subject, randomized, double-blind, and sham-controlled trial

BackgroundDevelopmental Dyslexia (DD) is a brain-based developmental disorder characterized by severe impairments in the acquisition of fluent and/or accurate reading. The extensive data on the neurobiology of DD have increased interest in brain-directed approaches. Transcranial direct current stimulation (tDCS) has been proposed as a non-invasive method to address reading difficulties in individuals with DD. While overall positive outcomes have been observed, the results remain heterogeneous. To enhance the current findings, various modalities have been employed, including manipulation of electrode montages, experimental designs, and targeting different brain regions. However, no studies have yet investigated the comparative effects of two different types of transcranial electrical stimulation, namely tDCS and transcranial random noise stimulation (tRNS), on reading abilities in children and adolescents with DD. MethodsThe present study will apply a within-subject, randomized, double-blind, and sham-controlled design. The aim of the present study is to investigate the effects of tDCS and tRNS on reading abilities in children and adolescents with DD. Participants will undergo three conditions, each separated by a one-week interval: (A) a single session of active tDCS; (B) a single session of active tRNS; and (C) a single session of sham (tDCS or sham tRNS). The order of the sessions will be counter-matched among participants. Left anodal/right cathodal tDCS and bilateral tRNS will be applied over the temporo-parietal regions for a duration of 20 minutes. The assessment of text, word, and non-word reading measures will be conducted immediately before and during each stimulation sessions. Safety, tolerability and blinding parameters will be assessed using a questionnaire. ResultsOur hypothesis is that tRNS will demonstrate comparable effectiveness to tDCS in improving text, word, and non-word reading measures compared to the sham conditions. Additionally, we anticipate that tRNS will exhibit a similar safety profile to tDCS. ConclusionThis study has the potential to contribute novel insights into the effectiveness of tRNS, a newly-wave tES method that has not yet been explored in children and adolescents with DD. Furthermore, findings may lay the groundwork for further investigations involving multiple tRNS sessions. Trial registrationThe study has been registered with ClinicalTrials.gov under the identifier NCT05832060.