On the Effects of Non-Invasive Brain Stimulation Techniques on Developmental Dyslexia: A Systematic Review of Randomized Controlled Trials

Azam  Naghavi; Hooshang  Dadgar; Ghazal  Daraei; Amin  Modarreszadeh

doi:10.18502/ijps.v20i2.18203

Azam Naghavi Department of Speech Therapy, School of Rehabilitation, Tehran University of Medical Sciences, Tehran, Iran.
Hooshang Dadgar Department of Speech Therapy, School of Rehabilitation, Tehran University of Medical Sciences, Tehran, Iran.
Ghazal Daraei Institute for Cognitive Science Studies (ICSS), Tehran, Iran.
Amin Modarreszadeh School of Rehabilitation, Tehran University of Medical Sciences, Tehran, Iran.

DOI: https://doi.org/10.18502/ijps.v20i2.18203

Keywords: Developmental Dyslexia; Magnetic Stimulation; Reading; Systematic Review; tDCS; Transcranial; Transcranial Electrical Stimulations

Abstract

Objective: Non-invasive brain stimulation (NIBS) can safely influence brain activity, enhancing cognitive functions and offering potential benefits for learning disabilities like dyslexia. This paper aims to fill the current gap in comprehensive reviews on NIBS studies specifically targeting dyslexic individuals.

Method: we conducted a systematic review across several databases, including PubMed, Web of Science, Scopus, Google Scholar, and CENTRAL Cochrane. The initial search strategy was designed to be as comprehensive as possible to capture all pertinent studies. We did not impose any language restrictions or time constraints during our search. The strategy was initially created using MEDLINE MeSH terms and subsequently adapted for the other databases. Our search included the keywords “dyslexia” in combination with “NIBS”, “transcranial magnetic stimulation (TMS)”, “transcranial direct current stimulation (tDCS)”, and other NIBS types like repetitive TMS and transcranial alternating current stimulation (tACS).

Results: 17 randomized controlled trial (RCT) studies were found to meet the eligibility criteria and are included in this review. Findings showed that repeated tDCS sessions, when paired with reading interventions, can effectively enhance reading abilities. Studies indicate that anodal tDCS applied to the left temporo‐parietal cortex (TPC) and cathodal tDCS to the right TPC, along with phonology-based reading training, have led to improvements in various reading metrics, including the reading of pseudo-words and low-frequency words. Notably, traditional reading areas appear to respond well to modulation through NIBS, and facilitative protocols can enhance various subprocesses related to reading.

Conclusion: Research indicates that tDCS, when used with reading interventions, enhances specific reading skills in individuals with dyslexia. Additionally, gamma-tACS applied to the left auditory cortex yields short-term improvements in neurophysiological responses to auditory stimuli. However, further randomized controlled trials with long-term follow-ups are necessary to establish the clinical effectiveness of these interventions.