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

Many interventions for reading difficulties in dyslexia are behaviorally-based. Specifically, such interventions are grounded on theories focusing on specific cognitive mechanisms related to reading, such as phonological processing, visuospatial attention, and the association between graphemes and phonemes (Archer et al., 2020; Vidyasagar, 2019). In the context of recent research on the dysfunction of neural oscillations in patients with dyslexia, the theory has emerged that neuromodulation could be a potential targeted therapy to improve the reading skills of individuals with functional deficits (Marchesotti et al., 2020; Turker & Hartwigsen, 2022). Observations by the authors mentioned above have shown a correlation between improved behavioral outcomes and the subsequent neurofunctional reorganization achieved by neuromodulation intervention, supporting the hypothesis that this intervention may offer considerable benefits in the treatment of dyslexia ((Marchesotti et al., 2020; Rufener & Zaehle, 2021; Turker & Hartwigsen, 2022). Neuromodulation refers to a set of techniques used to influence brain activity through stimulation or inhibition of specific regions of the brain. Transcranial Electrical Stimulation (tES) comprises a set of noninvasive techniques that aim to improve adaptive neural activity patterns and rehabilitate maladaptive ones (Moreno-Duarte et al., 2014). These techniques include transcranial direct current stimulation (tDCS), transcranial random noise stimulation (tRNS), and transcranial alternating current stimulation (tACS). These techniques use different-sized electrodes that can be placed differently depending on whether more or less focal stimulation is desired (Moreno-Duarte et al., 2014). Its application allows for modulating the activity of neural circuits in the brain, potentially affecting brain plasticity and promoting positive changes in brain functioning (Krause & Cohen Kadosh, 2013; Van der Groen et al., 2022). One widely used neuromodulation technique is the transcranial alternating current (tACS). Like other tES techniques, it consists of applying a weak electric current directly to the scalp, (Nitsche & Paulus, 2000), delivering a low-intensity current capable of passing through the scalp and affecting neuronal function. tACS uses sine waves at various frequencies with intensity (current) varying between 0.25 - 1 mA, and voltage of 5 - 15 mV. Moreover, it does not induce neuronal firing by suprathreshold depolarization of the neuronal membrane but rather modulates the spontaneous activity of the neuronal network.