Neuromodulation and behavioral approaches for the improvement of dyslexia symptoms in Slovenian-speaking children and adolescents

Developmental Dyslexia is one of the most common learning disabilities characterized by a variety of symptoms typically affecting reading and spelling. It is estimated that it affects around 5–10% of school children worldwide (Wagner et al., 2020). Its consequences can impact all aspects of an individual’s life, resulting to reduced socio-economic outcomes cross-culturally (Aro et al., 2019) and very often to emotional and behavioral difficulties (Xiao et al., 2022). Throughout the years, various theories have been proposed trying to explain the symptoms and understand the underlying deficit. The most prevailing among them is that dyslexia results from a phonological coding deficit (Ramus et al., 2006). This means that individuals with dyslexia have difficulties with decoding and identifying phonological properties of speech input, as well as accessing phonological representations in the brain (Shaywitz & Shaywitz, 2005). Another important aspect of dyslexia is its developmental status. Dyslexia is detected when children become acquainted with written language, around school time and it persists through adulthood. However, there are studies showing the underlying deficit evolves along the course of development, thus the necessity for homogeneous groups. Finally, neuroimaging studies have shown differences in brain activation patterns between typical and dyslexic individuals, with the main finding being hypo-activations in two posterior left hemisphere regions: 1) a dorsal, temporoparietal region, which is thought to be crucial for phonological processing and phoneme–grapheme conversion; 2) a ventral, occipitotemporal region, including the so-called visual word form area, which is thought to participate in whole word recognition. In the recent years, a large number of interventions and therapies, derived from various treatment approaches, have been constructed and evaluated with, somehow, promising results. Most of them target poor phonological awareness, as it has been shown to be possible to enhance by training (Wolff, 2014). However, the benefits do not extent to every possible affected domain, making their success rate questionable. In response to this, Non-Invasive-Brain Stimulation techniques, such as Transcranial Magnetic Stimulation (TMS) and transcranial Direct Current Stimulation (t-DCS) have been used providing benefits for children and adolescents, with long-lasting effects as well. However, the scarcity of these studies does not allow us to make firm conclusions about the effect of neuromodulation in the improvement of reading in dyslexia. With the above in mind, the present study will focus on the following: 1) define in a systematic way the symptoms of DD in Slovenian, a language with shallow orthography, by approaching reading and spelling as two distinct domains and children as distinct population from adolescents 2) incorporate new advancements in transcranial direct current stimulation and combine it with behavioral therapies, 3) apply stimulation in two different regions, ventral vs. dorsal, in a way that will enable us drawing causal conclusions about the underlying mechanisms of dyslexia and brain function.