Long-lasting improvement following tDCS treatment combined with a training for reading in children and adolescents with dyslexia

Neural bases of reading fluency: A systematic review and meta-analysis

Reading fluency, the ability to read quickly and accurately, is a critical marker of successful reading and is notoriously difficult to improve in reading disabled populations. Despite its importance to functional literacy, fluency is a relatively under-studied aspect of reading, and the neural correlates of reading fluency are not well understood. Here, we review the literature of the neural correlates of reading fluency as well as rapid automatized naming (RAN), a task that is robustly related to reading fluency. In a qualitative review of the neuroimaging literature, we evaluated structural and functional MRI studies of reading fluency in readers from a range of skill levels. This was followed by a quantitative activation likelihood estimate (ALE) meta-analysis of fMRI studies of reading speed and RAN measures. We anticipated that reading speed, relative to untimed reading and reading-related tasks, would harness ventral reading pathways that are thought to enable the fast, visual recognition of words. The qualitative review showed that speeded reading taps the entire canonical reading network. The meta-analysis indicated a stronger role of the ventral reading pathway in rapid reading and rapid naming. Both reviews identified regions outside the canonical reading network that contribute to reading fluency, such as the bilateral insula and superior parietal lobule. We suggest that fluent reading engages both domain-specific reading pathways as well as domain-general regions that support overall task performance and discuss future avenues of research to expand our understanding of the neural bases of fluent reading.

Cognitive enhancement through technology: A review of transcranial electrical stimulation (TES) interventions in children and adolescents with specific learning disabilities

BACKGROUND

In recent years, the exploration of innovative interventions for addressing problems of children and adolescents with specific learning disabilities (SLD) has garnered significant attention within the realm of neurocognitive research. Transcranial electrical stimulation (TES) has emerged as a promising tool for enhancing cognitive skills in children, offering a non-invasive and safe method that may particularly benefit those with learning difficulties. We aimed to appraise the extent and the quality of studies about impact of TES on cognitive skills including academic skills in children and adolescents with SLD.

METHODS

A literature search was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Articles published between January 2000 and January 2024 were searched in PubMed, Embase, Scopus, Web of Science and Google Scholar. The study eligibility criteria were previously established according to the PICO model. The Physiotherapy Evidence Database (PEDro) scale and Cochrane Collaboration tool (ROB2) were used to assess the methodological quality and the risk of bias of the included studies, respectively.

RESULTS

The initial search yielded 1571 studies among which 30 studies were systematically reviewed. The total number of participants was 224 individuals (intervention: 114; control: 110). Findings showed significant improvements in reading skills such as text reading, high-frequency word reading speed and efficiency and mathematical skills. Conversely, other cognitive skills such as working memory were not improved in people with dyslexia and dyscalculia.

DISCUSSION

TES interventions can positively affect cognitive skills in children and adolescents with SLD; However, due to the small number of studies, medium methodological quality and high risk of bias, caution should be taken when interpreting the results.

Action video games and posterior parietal cortex neuromodulation enhance both attention and reading in adults with developmental dyslexia

The impact of action video games on reading performance has been already demonstrated in individuals with and without neurodevelopmental disorders. The combination of action video games and posterior parietal cortex neuromodulation by a transcranial random noise stimulation could enhance brain plasticity, improving attentional control and reading skills also in adults with developmental dyslexia. In a double blind randomized controlled trial, 20 young adult nonaction video game players with developmental dyslexia were trained for 15 h with action video games. Half of the participants were stimulated with bilateral transcranial random noise stimulation on the posterior parietal cortex during the action video game training, whereas the others were in the placebo (i.e. sham) condition. Word text reading, pseudowords decoding, and temporal attention (attentional blink), as well as electroencephalographic activity during the attentional blink, were measured before and after the training. The action video game + transcranial random noise stimulation group showed temporal attention, word text reading, and pseudoword decoding enhancements and P300 amplitude brain potential changes. The enhancement in temporal attention performance was related with the efficiency in pseudoword decoding improvement. Our results demonstrate that the combination of action video game training with parietal neuromodulation increases the efficiency of visual attention deployment, probably reshaping goal-directed and stimulus-driven fronto-parietal attentional networks interplay in young adults with neurodevelopmental conditions.

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

Background

Developmental Dyslexia (DD) is a brain-based developmental disorder causing severe reading difficulties. The extensive data on the neurobiology of DD have increased interest in brain-directed approaches, such as transcranial direct current stimulation (tDCS), which have been proposed for DD. While positive outcomes have been observed, results remain heterogeneous. Various methodological approaches have been employed to address this issue. However, no studies have compared the effects of different transcranial electrical stimulation techniques (e.g., tDCS and transcranial random noise stimulation, tRNS), on reading in children and adolescents with DD.

Methods

The present within-subject, double-blind, and sham-controlled trial aims to investigate the effects of tDCS and hf-tRNS on reading in children and adolescents with DD. Participants will undergo three conditions with a one-week interval session: (A) single active tDCS session; (B) single active hf-tRNS session; and (C) single sham session (tDCS/hf-tRNS). Left anodal/right cathodal tDCS and bilateral tRNS will be applied over the temporo-parietal regions for 20 min each. Reading measures will be collected before and during each session. Safety and blinding parameters will be recordered.

Discussion

We hypothesize that tRNS will demonstrate comparable effectiveness to tDCS in improving reading compared to sham conditions. Additionally, we anticipate that hf-tRNS will exhibit a similar safety profile to tDCS. This study will contribute novel insights into the effectiveness of hf-tRNS, expediting the validation of brain-based treatments for DD.

Combined multi-session transcranial alternating current stimulation (tACS) and language skills training improves individual gamma band activity and literacy skills in developmental dyslexia

Developmental dyslexia is characterized by the pathologically diminished ability to acquire reading and spelling skills. Accurate processing of acoustic information at the phonemic scale is crucial for successful sound-to-letter-mapping which, in turn, is elemental in reading and spelling. Altered activation patterns in the auditory cortex are thought to provide the neurophysiological basis for the inaccurate phonemic perception. Recently, transcranial electrical stimulation has been shown to be an effective method to ameliorate cortical activation patterns in the auditory cortex. In a sample of children and adolescents with dyslexia, we investigated the effect of multi-session transcranial alternating current stimulation delivered concurrently with a phonological training and in combination with a behavioral literacy skills training. Over a 5-week period the participants received 10 training sessions while gamma-tACS was administered over bilateral auditory cortex. We found that gamma-tACS shifted the peak frequency of auditory gamma oscillations reflecting a more fine-grained processing of time-critical acoustic information. This amelioration was accompanied by increased phonemic processing skills. Moreover, individuals who received gamma-tACS showed significant improvements in their spelling skills four months after the intervention. Our results demonstrate that multi-session gamma-tACS enhances the effects of a behavioral intervention and induces long-term improvement on literacy skills in dyslexia.

Adaptive short-term plasticity in the typical reading network

The left temporo-parietal cortex (TPC) is crucial for phonological decoding, i.e., for learning and retaining sound-letter mappings, and appears hypoactive in dyslexia. Here, we tested the causal contribution of this area for reading in typical readers with transcranial magnetic stimulation (TMS) and explored the reading network's response with fMRI. By investigating the underlying neural correlates of stimulation-induced modulations of the reading network, we can help improve targeted interventions for individuals with dyslexia. 28 typical adult readers overtly read simple and complex words and pseudowords during fMRI after effective and sham TMS over the left TPC. To explore differences in functional activation and effective connectivity within the reading network, we performed univariate and multivariate analyses, as well as dynamic causal modeling. While TMS-induced effects on reading performance and brain activation showed large individual variability, multivariate analyses revealed a shift in activation in the left inferior frontal cortex for pseudoword reading after effective TMS. Furthermore, TMS increased effective connectivity from the left ventral occipito-temporal cortex to the left TPC. In the absence of effects on reading performance, the observed changes in task-related activity and the increase in functional coupling between the two core reading nodes suggest successful short-term compensatory reorganization in the reading network following TMS-induced disruption. This study is the first to explore neurophysiological changes induced by TMS to a core reading node in typical readers while performing an overt reading task. We provide evidence for remote stimulation effects and emphasize the relevance of functional interactions in the reading network.

The efficacy of non-invasive brain stimulation in the treatment of children and adolescents with Anorexia Nervosa: study protocol of a randomized, double blind, placebo-controlled trial

BACKGROUND

Current psychological and pharmacological treatments for Anorexia Nervosa (AN) provide only moderate effective support, and there is an urgent need for research to improve therapies, especially in developing age. Non-invasive brain stimulation has suggested to have the potential to reducing AN symptomatology, via targeting brain alterations, such as hyperactivity of right prefrontal cortex (PFC). We suppose that transcranial direct current stimulation (tDCS) to the PFC may be effective in children and adolescents with AN.

METHODS

We will conduct a randomized, double blind, add-on, placebo-controlled trial to investigate the efficacy of tDCS treatment on clinical improvement. We will also investigate brain mechanisms and biomarkers changes acting in AN after tDCS treatment. Eighty children or adolescent with AN (age range 10-18 years) will undergo treatment-as-usual including psychiatric, nutritional and psychological support, plus tDCS treatment (active or sham) to PFC (F3 anode/F4 cathode), for six weeks, delivered three times a week. Psychological, neurophysiological and physiological measures will be collected at baseline and at the end of treatment. Participants will be followed-up one, three, six months and one year after the end of treatment. Psychological measures will include parent- and self-report questionnaires on AN symptomatology and other psychopathological symptoms. Neurophysiological measures will include transcranial magnetic stimulation (TMS) with electroencephalography and paired pulse TMS and repetitive TMS to investigate changes in PFC connectivity, reactivity and plasticity after treatment. Physiological measures will include changes in the functioning of the endogenous stress response system, body mass index (BMI) and nutritional state.

DISCUSSION

We expect that tDCS treatment to improve clinical outcome by reducing the symptoms of AN assessed as changes in Eating Disorder Risk composite score of the Eating Disorder Inventory-3. We also expect that at baseline there will be differences between the right and left hemisphere in some electrophysiological measures and that such differences will be reduced after tDCS treatment. Finally, we expect a reduction of endogenous stress response and an improvement in BMI and nutritional status after tDCS treatment. This project would provide scientific foundation for new treatment perspectives in AN in developmental age, as well as insight into brain mechanisms acting in AN and its recovery. Trial registration The study was registered at ClinicalTrials.gov (ID: NCT05674266) and ethical approval for the study was granted by the local research ethics committee (process number 763_OPBG_2014).

Effects of the Visual Praxis-Based Occupational Therapy Education Program on different kinds of reading skills: Single-blind randomized follow-up study

This study aims to examine the long-term effects of Visual Praxis Based Occupational Therapy Program (VP-OTP) on the reading skills of children with Developmental Dyslexia. A total of 126 children with Developmental Dyslexia participated in the study. The participants were then divided into two groups (Intervention and Control groups) of equal sizes (n = 63) using a random number generator without replacement. The intervention group received VP-OTP in two weekly sessions for 8 weeks. All participants were assessed with the Oral Reading Skills and Comprehension Test-II (Sobat®-II) at three time points; pretest, post-test, and follow-up. The intervention group showed promising results as the Sobat®-II's Reading Accuracy, Reading Speed, Fluent Reading, Reading Comprehension Total Score significantly increased after the intervention (p ≤ 0.05) and the scores were maintained at the follow-up (p > 0.05). The VP-OTP intervention provided a maintained improvement in reading skills of children with Developmental Dyslexia.

The effect of non-invasive vagus nerve stimulation on memory recall in reading: A pilot study

Expert reading acquisition is marked by fluent, effortless decoding, and adequate comprehension skills and is required for modern daily life. In spite of its importance, many individuals struggle with reading comprehension even when decoding skills are adequate. Unfortunately, effective reading comprehension interventions are limited, especially for adults. A growing body of research suggests that non-invasive transcutaneous stimulation of the auricular vagus nerve (taVNS) may drive neural plasticity for low-level reading skills such as speech sound perception and letter-sound learning, but it is unknown whether taVNS can improve higher level skills as well. Thus, the current pilot study was designed to evaluate the effect of taVNS paired with passage reading on reading comprehension performance. Twenty-four typically developing young adults were recruited and screened for baseline reading and working memory skills. Participants received either sham or active taVNS while reading short passages out loud. Immediately following each passage, participants answered a series of test questions that required either direct recall of passage details or more complete comprehension of the passage content. While taVNS did not improve the mechanics of reading (e.g., reading rate or accuracy), there was a significant effect of active taVNS on test performance. This effect was driven by significant improvement on accuracy for memory questions while there was no effect of taVNS on comprehension question accuracy. These findings suggest that taVNS may be beneficial for enhancing memory, but its efficacy may be limited in higher cognitive domains.

Improving Swallowing Function and Ability in Post Stroke Dysphagia: A Randomized Clinical Trial

Post-stroke dysphagia is a prevalent, life threatening condition. Scientists recommended implementing behavioral therapies with new technologies such as transcranial direct current of stimulation (TDCS). Studies showed promising TDCS effects, and scientists suggested the investigation of the effectiveness of different montages. Supramarginal gyrus (SMG) is important in swallowing function. Our study aimed to investigate the effectiveness of stimulating SMG in improving post-stroke dysphagia. Forty-four patients finished the study (a randomized, double-blind one). All of them received behavioral therapy. The real group received anodal (2 mA, 20 min) stimulation on the intact SMG, and the sham group received the same for 30 s (5 sessions). Patients were assessed with Functional Oral Intake Scale (FOIS) and Mann Assessment of Swallowing Ability (MASA) after treatment and at one-month follow-up. The results showed that the difference between groups at baseline was not significant. According to MASA both groups improved significantly during the time (p-value < 0.001). The improvement in the real group was significantly higher than in the sham group after treatment (p-value = 0.002) and after one-month follow-up (p-value < 0.001). According to FOIS, most of the patients in the real group (72.70%) reached level 6 or 7 after one-month follow-up which was significantly higher than the sham group (31.80%, p-value = 0.007). In conclusion, TDCS applied to the scalp's surface associated with SMG localization may improve swallowing function in the stroke patients with dysphagia.

Exploring Genetic and Neural Risk of Specific Reading Disability within a Nuclear Twin Family Case Study: A Translational Clinical Application

Imaging and genetic studies have characterized biological risk factors contributing to specific reading disability (SRD). The current study aimed to apply this literature to a family of twins discordant for SRD and an older sibling with reading difficulty. Intraclass correlations were used to understand the similarity of imaging phenotypes between pairs. Reading-related genes and brain region phenotypes, including asymmetry indices representing the relative size of left compared to right hemispheric structures, were descriptively examined. SNPs that corresponded between the SRD siblings and not the typically developing (TD) siblings were in genes ZNF385D, LPHN3, CNTNAP2, FGF18, NOP9, CMIP, MYO18B, and RBFOX2. Imaging phenotypes were similar among all sibling pairs for grey matter volume and surface area, but cortical thickness in reading-related regions of interest (ROIs) was more similar among the siblings with SRD, followed by the twins, and then the TD twin and older siblings, suggesting cortical thickness may differentiate risk for this family. The siblings with SRD had more symmetry of cortical thickness in the transverse temporal and superior temporal gyri, while the TD sibling had greater rightward asymmetry. The TD sibling had a greater leftward asymmetry of grey matter volume and cortical surface area in the fusiform, supramarginal, and transverse temporal gyrus. This exploratory study demonstrated that reading-related risk factors appeared to correspond with SRD within this family, suggesting that early examination of biological factors may benefit early identification. Future studies may benefit from the use of polygenic risk scores or machine learning to better understand SRD risk.

Modulation of auditory temporal processing, speech in noise perception, auditory-verbal memory, and reading efficiency by anodal tDCS in children with dyslexia

Dyslexia is a neurodevelopmental disorder that is prevalent in children. It is estimated that 30-50% of individuals diagnosed with dyslexia also manifest an auditory perceptual deficit characteristic of auditory processing disorder (APD). Some studies suggest that defects in basic auditory processing can lead to phonological defects as the most prominent cause of dyslexia. Thus, in some cases, there may be interrelationships between dyslexia and some of the aspects of central auditory processing. In recent years, transcranial direct current stimulation (tDCS) has been used as a safe method for the modulation of central auditory processing aspects in healthy adults and reading skills in children with dyslexia. Therefore, the objectives of our study were to investigate the effect of tDCS on the modulation of different aspects of central auditory processing, aspects of reading, and the relationship between these two domains in dyslexic children with APD. A within-subjects design was employed to investigate the effect of two electrode arrays (the anode on the left STG (AC)/cathode on the right shoulder and anode on the left STG/cathode on the right STG) on auditory temporal processing; speech-in-noise perception, short-term auditory memory; and high-frequency word, low-frequency word, pseudoword, and text reading. The results of this clinical trial showed the modulation of the studied variables in central auditory processing and the accuracy and speed of reading variables compared to the control and sham statuses in both electrode arrays. Our results also showed that the improvement of the accuracy and speed of text reading, as well as the accuracy of pseudoword reading were related to the improvement of speech in noise perception and temporal processing. The results of this research can be effective in clarifying the basis of the neurobiology of dyslexia and, in particular, the hypothesis of the role of basic auditory processing and subsequently the role of the auditory cortex in dyslexia. These results might provide a framework to facilitate behavioral rehabilitation in dyslexic children with APD.

Extraction of discriminative features from EEG signals of dyslexic children; before and after the treatment

Dyslexia is a neurological disorder manifested as difficulty reading and writing. It can occur despite adequate instruction, intelligence, and intact sensory abilities. Different electroencephalogram (EEG) patterns have been demonstrated between dyslexic and healthy subjects in previous studies. This study focuses on the difference between patients before and after treatment. The main goal is to identify the subset of features that adequately discriminate subjects before and after a specific treatment plan. The treatment consists of Transcranial Direct Current Stimulation (tDCS) and occupational therapy using the BrainWare SAFARI software. The EEG signals of sixteen dyslexic children were recorded during the eyes-closed resting state before and after treatment. The preprocessing step was followed by the extraction of a wide range of features to investigate the differences related to the treatment. An optimal subset of features extracted from recorded EEG signals was determined using Principal Component Analysis (PCA) in conjunction with the Sequential Floating Forward Selection (SFFS) algorithm. The results showed that treatment leads to significant changes in EEG features like spectral and phase-related EEG features, in various regions. It has been demonstrated that the extracted subset of discriminative features can be useful for classification applications in treatment assessment. The most discriminative subset of features could classify the data with an accuracy of 92% with SVM classifier. The above result confirms the efficacy of the treatment plans in improving dyslexic children's cognitive skills.

The effects of bilateral posterior parietal cortex tRNS on reading performance

According to established cognitive neuroscience knowledge based on studies on disabled and typically developing readers, reading is based on a dual-stream model in which a phonological-dorsal stream (left temporo-parietal and inferior frontal areas) processes unfamiliar words and pseudowords, whereas an orthographic-ventral stream (left occipito-temporal and inferior frontal areas) processes known words. However, correlational neuroimaging, causal longitudinal, training, and pharmacological studies have suggested the critical role of visuo-spatial attention in reading development. In a double blind, crossover within-subjects experiment, we manipulated the neuromodulatory effect of a short-term bilateral stimulation of posterior parietal cortex (PPC) by using active and sham tRNS during reading tasks in a large sample of young adults. In contrast to the dual-stream model predicting either no effect or a selective effect on the stimulated phonological-dorsal stream (as well as to a general multisensory effect on both reading streams), we found that only word-reading performance improved after active bilateral PPC tRNS. These findings demonstrate a direct neural connectivity between the PPC, controlling visuo-spatial attention, and the ventral stream for visual word recognition. These results support a neurobiological model of reading where performance of the orthographic-ventral stream is boosted by an efficient deployment of visuo-spatial attention from bilateral PPC stimulation.

Effects of a short and intensive transcranial direct current stimulation treatment in children and adolescents with developmental dyslexia: A crossover clinical trial

Developmental Dyslexia (DD) significantly interferes with children’s academic, personal, social, and emotional functioning. Nevertheless, therapeutic options need to be further validated and tested in randomized controlled clinical trials. The use of transcranial direct current stimulation (tDCS) has been gaining ground in recent years as a new intervention option for DD. However, there are still open questions regarding the most suitable tDCS protocol for young people with DD. The current crossover study tested the effectiveness of a short and intensive tDCS protocol, including the long-term effects, as well as the influence of age and neuropsychological processes at baseline on reading improvements. Twenty-four children and adolescents with DD were randomly assigned to receive active tDCS during the first slot and sham tDCS during the second slot or vice versa. Five consecutive daily sessions of left anodal/right cathodal tDCS set at 1 mA for 20 min were administered over the parieto-occipital regions. Reading measures (text, high frequency word, low frequency word, and non-word lists) and neuropsychological measures (visual-spatial and verbal working memory, phoneme blending, and rapid automatized naming tasks) were collected before, immediately after, 1 week and 1 month later the treatment. Our results showed that only the active tDCS condition improved non-word reading speed immediately after and 1 month later the end of the treatment compared with baseline. In addition, the improvement in non-word reading speed was significantly correlated with age and with neuropsychological measures (verbal working memory and phoneme blending) at baseline but only in the active tDCS condition. The current crossover study contributed to enforce previous effects of tDCS, including long-term effects, on non-word reading speed and to understand the effect of age and neuropsychological processes on reading outcomes. Our findings showed that tDCS could be a low-cost and easy-to-implement treatment option with long-term effects for children and adolescents with DD.

A systematic review of randomized controlled trials on efficacy and safety of transcranial direct current stimulation in major neurodevelopmental disorders: ADHD, autism, and dyslexia

OBJECTIVE

Among the target groups in child and adolescent psychiatry, transcranial direct current stimulation (tDCS) has been more applied in neurodevelopmental disorders specifically, attention-deficit hyperactivity disorder (ADHD), autism spectrum disorder (ASD), and dyslexia. This systematic review aims to provide the latest update on published randomized-controlled trials applying tDCS in these disorders for evaluating its efficacy and safety.

METHODS

Based on a pre-registered protocol (PROSPERO: CRD42022321430) and using the PRISMA approach, a literature search identified 35 randomized controlled trials investigating the effects of tDCS on children and adolescents with ADHD (n = 17), ASD (n = 11), and dyslexia (n = 7).

RESULTS

In ADHD, prefrontal anodal tDCS is reported more effective compared to stimulation of the right inferior frontal gyrus. Similarly in ASD, prefrontal anodal tDCS was found effective for improving behavioral problems. In dyslexia, stimulating temporoparietal regions was the most common and effective protocol. In ASD and dyslexia, all tDCS studies found an improvement in at least one of the outcome variables while 64.7% of studies (11 of 17) in ADHD found a similar effect. About 88% of all tDCS studies with a multi-session design in 3 disorders (16 of 18) reported a significant improvement in one or all outcome variables after the intervention. Randomized, double-blind, controlled trials consisted of around 70.5%, 36.3%, and 57.1% of tDCS studies in ADHD, ASD, and dyslexia, respectively. tDCS was found safe with no reported serious side effects in 6587 sessions conducted on 745 children and adolescents across 35 studies.

CONCLUSION

tDCS was found safe and partially effective. For evaluation of clinical utility, larger randomized controlled trials with a double-blind design and follow-up measurements are required. Titration studies that systematically evaluate different stimulation intensities, duration, and electrode placement are lacking.

Efficacy of transcranial Direct Current Stimulation (tDCS) combined with intensive speech therapy for language production in monozygotic twins with corpus callosum dysgenesis (CCD): A sham-controlled single subject study

The purpose of this single subject study was to investigate whether transcranial direct current stimulation (tDCS) applied to both hemispheres combined with speech therapy can improve language learning in a pair of 5-year-old twins with corpus callosum dysgenesis (CCD). The treatment protocol included anodal tDCS with simultaneous speech therapy in one of the participants (T.D.), and sham-tDCS with the same montage, and stimulation regime concomitant with speech therapy for the other twin (A.D.). Our findings show that T.D. improved in language production when treated with speech therapy in combination with tDCS. A.D. showed evidence for a relatively minor behavioral benefit from speech therapy.

The use of noninvasive brain stimulation techniques to improve reading difficulties in dyslexia: A systematic review

Noninvasive brain stimulation (NIBS) allows to actively and noninvasively modulate brain function. Aside from inhibiting specific processes, NIBS may also enhance cognitive functions, which might be used for the prevention and intervention of learning disabilities such as dyslexia. However, despite the growing interest in modulating learning abilities, a comprehensive, up-to-date review synthesizing NIBS studies with dyslexics is missing. Here, we fill this gap and elucidate the potential of NIBS as treatment option in dyslexia. The findings of the 15 included studies suggest that repeated sessions of reading training combined with different NIBS protocols may induce long-lasting improvements of reading performance in child and adult dyslexics, opening promising avenues for future research. In particular, the "classical" reading areas seem to be most successfully modulated through NIBS, and facilitatory protocols can improve various reading-related subprocesses. Moreover, we emphasize the need to further explore the potential to modulate auditory cortex function as a preintervention and intervention approach for affected children, for example, to avoid the development of auditory and phonological difficulties at the core of dyslexia. Finally, we outline how future studies may increase our understanding of the neurobiological basis of NIBS-induced improvements in dyslexia.

Brain stimulation: a therapeutic approach for the treatment of neurological disorders

Brain stimulation has become one of the most acceptable therapeutic approaches in recent years and a powerful tool in the remedy against neurological diseases. Brain stimulation is achieved through the application of electric currents using non-invasive as well as invasive techniques. Recent technological advancements have evolved into the development of precise devices with capacity to produce well-controlled and effective brain stimulation. Currently, most used non-invasive techniques are repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS), whereas the most common invasive technique is deep brain stimulation (DBS). In last decade, application of these brain stimulation techniques has not only exploded but also expanded to wide variety of neurological disorders. Therefore, in the current review, we will provide an overview of the potential of both non-invasive (rTMS and tDCS) and invasive (DBS) brain stimulation techniques in the treatment of such brain diseases.

The Effects of tDCS with NDT on the Improvement of Motor Development in Cerebral Palsy

We investigated the effects of transcranial direct current stimulation (tDCS) over the primary motor cortex (M1) with neurodevelopmental treatment (NDT) on the improvement of motor development and reduction of spasticity in children with cerebral palsy (CP). Twenty-four children with CP were allocated to two groups: the tDCS + NDT group and the only NDT group, done 3 times per week for 5 weeks. The Gross Motor Function Measurement (GMFM-88) and Box and Block Test (BBT) were used to assess changes in motor development, and the Modified Ashworth Scale (MAS) was used to evaluate changes in spasticity. All measurements were carried out at 3 time points: baseline, post-intervention, and 1 month follow-up. We found improvements in the GMFM-88 total scores and in each individual GMFM-88 dimension scores, favoring the tDCS + NDT group over the only NDT group. The BBT scores improved only in the tDCS + NDT group. In addition, the MAS scores reduced in the hemibody with significant motor impairment only in the tDCS + NDT group. The present findings suggest that tDCS combined with NDT can be considered a promising intervention for children with CP, as it can enhance motor development and reduce spasticity in this population.

Using Neurofeedback to Restore Inter-Hemispheric Imbalance: A Study Protocol for Adults With Dyslexia

Neurofunctional models of developmental dyslexia (DD) point out disruption of the left-lateralized reading network. In individuals with DD, the left temporo-parietal (TP) regions are underactivated during reading tasks and a dysfunctional activation of the contralateral regions is reported. After a successful reading intervention, left TP lateralization was found to be increased in children with DD. Previous studies measured the effect of modulating the excitability of the left TP cortex using non-invasive brain stimulation (NIBS) in individuals with reading difficulties, showing significant reading improvements. NIBS exclusion criteria and safety guidelines may limit its application in settings without medical supervision and in younger populations. Neurofeedback (NF) training could be an alternative intervention method for modulating the inter-hemispheric balance of the temporal–parietal regions in DD. To date, the effect of NF on reading has been scarcely investigated. Few protocols increasing beta activity in underactivated areas showed improved reading outcomes. However, none of the previous studies designed the NF intervention based on a neurofunctional model of DD. We aim to propose a study protocol for testing the efficacy of a NF training specifically designed for inducing a functional hemispheric imbalance of the tempo-parietal regions in adults with DD. A randomized clinical trial aimed at comparing two experimental conditions is described: (a) Enhancing left beta/theta power ratio NF training in combination with reducing right beta/theta power ratio NF training and (b) sham NF training.

Clinical Trial Registration:www.ClinicalTrials.gov, identifier [NCT04989088].

Boosting Numerical Cognition in Children and Adolescents with Mathematical Learning Disabilities by a Brain-Based Intervention: A Study Protocol for a Randomized, Sham-Controlled Clinical Trial

Numbers are everywhere, and supporting difficulties in numerical cognition (e.g., mathematical learning disability (MLD)) in a timely, effective manner is critical for their daily use. To date, only low-efficacy cognitive-based interventions are available. The extensive data on the neurobiology of MLD have increased interest in brain-directed approaches. The overarching goal of this study protocol is to provide the scientific foundation for devising brain-based and evidence-based treatments in children and adolescents with MLD. In this double-blind, between-subject, sham-controlled, randomized clinical trial, transcranial random noise stimulation (tRNS) plus cognitive training will be delivered to participants. Arithmetic, neuropsychological, psychological, and electrophysiological measures will be collected at baseline (T0), at the end of the interventions (T1), one week (T2) and three months later (T3). We expect that tRNS plus cognitive training will significantly improve arithmetic measures at T1 and at each follow-up (T2, T3) compared with placebo and that such improvements will correlate robustly and positively with changes in the neuropsychological, psychological, and electrophysiological measures. We firmly believe that this clinical trial will produce reliable and positive results to accelerate the validation of brain-based treatments for MLD that have the potential to impact quality of life.

Neuroplasticity and non-invasive brain stimulation in the developing brain

The brain is a dynamic organ whose growth and organization varies according to each subject's life experiences. Through adaptations in gene expression and the release of neurotrophins and neurotransmitters, these experiences induce a process of cellular realignment and neural network reorganization, which consolidate what is called neuroplasticity. However, despite the brain's resilience and dynamism, neuroplasticity is maximized during the first years of life, when the developing brain is more sensitive to structural reorganization and the repair of damaged neurons. This review presents an overview of non-invasive brain stimulation (NIBS) techniques that have increasingly been a focus for experimental research and the development of therapeutic methods involving neuroplasticity, especially Transcranial Magnetic Stimulation (TMS) and Transcranial Direct Current Stimulation (tDCS). Due to its safety risk profile and extensive tolerability, several trials have demonstrated the benefits of NIBS as a feasible experimental alternative for the treatment of brain and mind disorders in children and adolescents. However, little is known about the late impact of neuroplasticity-inducing tools on the developing brain, and there are concerns about aberrant plasticity. There are also ethical considerations when performing interventions in the pediatric population. This article will therefore review these aspects and also obstacles related to the premature application of NIBS, given the limited evidence available concerning the extent to which these methods interfere with the developing brain.

DUAL-tDCS Treatment over the Temporo-Parietal Cortex Enhances Writing Skills: First Evidence from Chronic Post-Stroke Aphasia

The learning of writing skills involves the re-engagement of previously established independent procedures. Indeed, the writing deficit an adult may acquire after left hemispheric brain injury is caused by either an impairment to the lexical route, which processes words as a whole, to the sublexical procedure based on phoneme-to-grapheme conversion rules, or to both procedures. To date, several approaches have been proposed for writing disorders, among which, interventions aimed at restoring the sub-lexical procedure were successful in cases of severe agraphia. In a randomized double-blind crossover design, fourteen chronic Italian post-stroke aphasics underwent dual transcranial direct current stimulation (tDCS) (20 min, 2 mA) with anodal and cathodal current simultaneously placed over the left and right temporo-parietal cortex, respectively. Two different conditions were considered: (1) real, and (2) sham, while performing a writing task. Each experimental condition was performed for ten workdays over two weeks. After real stimulation, a greater amelioration in writing with respect to the sham was found. Relevantly, these effects generalized to different language tasks not directly treated. This evidence suggests, for the first time, that dual tDCS associated with training is efficacious for severe agraphia. Our results confirm the critical role of the temporo-parietal cortex in writing skills.

Dyslexia treatment studies: A systematic review and suggestions on testing treatment efficacy with small effects and small samples

Poor response to treatment is a defining characteristic of reading disorder. In the present systematic review and meta-analysis, we found that the overall average effect size for treatment efficacy was modest, with a mean standardized difference of 0.38. Small true effects, combined with the difficulty to recruit large samples, seriously challenge researchers planning to test treatment efficacy in dyslexia and potentially in other learning disorders. Nonetheless, most published studies claim effectiveness, generally based on liberal use of multiple testing. This inflates the risk that most statistically significant results are associated with overestimated effect sizes. To enhance power, we propose the strategic use of repeated measurements with mixed-effects modelling. This novel approach would enable us to estimate both individual parameters and population-level effects more reliably. We suggest assessing a reading outcome not once, but three times, at pre-treatment and three times at post-treatment. Such design would require only modest additional efforts compared to current practices. Based on this, we performed ad hoc a priori design analyses via simulation studies. Results showed that using the novel design may allow one to reach adequate power even with low sample sizes of 30–40 participants (i.e., 15–20 participants per group) for a typical effect size of d = 0.38. Nonetheless, more conservative assumptions are warranted for various reasons, including a high risk of publication bias in the extant literature. Our considerations can be extended to intervention studies of other types of neurodevelopmental disorders.

Visual search efficiency and functional visual cortical size in children with and without dyslexia

Dyslexia is characterised by poor reading ability. Its aetiology is probably multifactorial, with abnormal visual processing playing an important role. Among adults with normal reading ability, there is a larger representation of central visual field in the primary visual cortex (V1) in those with more efficient visuospatial attention. In this study, we tested the hypothesis that poor reading ability in school-aged children (17 children with dyslexia, 14 control children with normal reading ability) is associated with deficits in visuospatial attention using a visual search task. We corroborated the psychophysical findings with neuroimaging, by measuring the functional size of V1 in response to a central 12° visual stimulus. Consistent with other literature, visual search was impaired and less efficient in the dyslexic children, particularly with more distractor elements in the search array (p = 0.04). We also found atypical interhemispheric asymmetry in functional V1 size in the dyslexia group (p = 0.02). Reading impaired children showed poorer visual search efficiency (p = 0.01), needing more time per unit distractor (higher ms/item). Reading ability was also correlated with V1 size asymmetry (p = 0.03), such that poorer readers showed less left hemisphere bias relative to the right hemisphere. Our findings support the view that dyslexic children have abnormal visuospatial attention and interhemispheric V1 asymmetry, relative to chronological age-matched peers, and that these factors may contribute to inter-individual variation in reading performance in children.

tES to rehabilitate neurodevelopmental disorders: A study on clinical practitioners' attitudes

Crucial arguments in the debate about the use of transcranial electrical stimulation (tES) as an intervention for children with neurodevelopmental disorders include, besides safety and efficacy issues, neuroethical concerns as well. No agreement has been reached yet in the clinical community about the ethical aspects of stimulating, although not invasively, a developing brain. To investigate ethical concerns about the use of tES in childhood and adolescence, we explored the knowledge and opinions of practitioners (psychologists, pediatricians, child psychiatrists, and rehabilitators) working in the field of rehabilitation of neurodevelopmental disorders (N=106). An online survey was designed to collect information about what practitioners in the neurodevelopmental field think about the therapeutic use of tES in terms of ethical concerns, need for facilitating conditions, openness to alternative treatments, and need for usability. Findings showed that a previous knowledge of tES, the presence of facilitating circumstances, and lower ethical concerns were the stronger predictors of clinical professionals' propensity to use tES for children rehabilitation. The present study is the first to explore the attitudes of clinical professionals toward the therapeutic use of tES in developmental populations, which we claim are useful for furthering the communication directed to the clinical community and its involvement in the discussion about tES-related issues.

Beyond Reading Modulation: Temporo-Parietal tDCS Alters Visuo-Spatial Attention and Motion Perception in Dyslexia

Dyslexia is a neurodevelopmental disorder with an atypical activation of posterior left-hemisphere brain reading networks (i.e., temporo-occipital and temporo-parietal regions) and multiple neuropsychological deficits. Transcranial direct current stimulation (tDCS) is a tool for manipulating neural activity and, in turn, neurocognitive processes. While studies have demonstrated the significant effects of tDCS on reading, neurocognitive changes beyond reading modulation have been poorly investigated. The present study aimed at examining whether tDCS on temporo-parietal regions affected not only reading, but also phonological skills, visuo-spatial working memory, visuo-spatial attention, and motion perception in a polarity-dependent way. In a within-subjects design, ten children and adolescents with dyslexia performed reading and neuropsychological tasks after 20 min of exposure to Left Anodal/Right Cathodal (LA/RC) and Right Anodal/Left Cathodal (RA/LC) tDCS. LA/RC tDCS compared to RA/LC tDCS improved text accuracy, word recognition speed, motion perception, and modified attentional focusing in our group of children and adolescents with dyslexia. Changes in text reading accuracy and word recognition speed—after LA/RC tDCS compared to RA/LC—were related to changes in motion perception and in visuo-spatial working memory, respectively. Our findings demonstrated that reading and domain-general neurocognitive functions in a group of children and adolescents with dyslexia change following tDCS and that they are polarity-dependent.

Sleep-Related Declarative Memory Consolidation in Children and Adolescents with Developmental Dyslexia

Sleep has a crucial role in memory processes, and maturational changes in sleep electrophysiology are involved in cognitive development. Albeit both sleep and memory alterations have been observed in Developmental Dyslexia (DD), their relation in this population has been scarcely investigated, particularly concerning topographical aspects. The study aimed to compare sleep topography and associated sleep-related declarative memory consolidation in participants with DD and normal readers (NR). Eleven participants with DD and 18 NR (9-14 years old) underwent a whole-night polysomnography. They were administered a word pair task before and after sleep to assess for declarative memory consolidation. Memory performance and sleep features (macro and microstructural) were compared between the groups, and the intercorrelations between consolidation rate and sleep measures were assessed. DD showed a deeper worsening in memory after sleep compared to NR and reduced slow spindles in occipito-parietal and left fronto-central areas. Our results suggest specific alterations in local sleep EEG (i.e., sleep spindles) and in sleep-dependent memory consolidation processes in DD. We highlight the importance of a topographical approach, which might shed light on potential alteration in regional cortical oscillation dynamics in DD. The latter might represent a target for therapeutic interventions aimed at enhancing cognitive functioning in DD.

Effects of a short, intensive, multi-session tDCS treatment in developmental dyslexia: Preliminary results of a sham-controlled randomized clinical trial

Developmental Dyslexia (DD) significantly interferes with academic, personal, social and emotional functioning. Nevertheless, established therapeutic options are still scarce. Research has begun to emerge studying the potential action of transcranial direct current stimulation (tDCS) for ameliorating reading. However, there are still open questions regarding the most suitable tDCS protocol in young with DD. The current study tested the effectiveness of a short, intensive and multi-session tDCS protocol and presented preliminary data from a randomized sham-controlled crossover trial. Twenty-seven children and adolescents with DD were randomly assigned to active tDCS or sham tDCS. Active tDCS group received five daily-consecutive sessions of left anodal/right cathodal set at 1mA for 20min over parieto-occipital regions. Reading measures, including text, high frequency word, low frequency word and non-word lists, were recorded before, immediately after the treatment and 1-week later. We found that only the active tDCS group ameliorated non-word reading speed immediately after and 1-week later the end of the treatment compared to the baseline. Some suggestions for the development of future tDCS protocols in children and adolescents with DD are given.

Effects of transcranial stimulation in developmental neurocognitive disorders: A critical appraisal

Non-invasive brain stimulation (NIBS) has been highlighted as a powerful tool to promote neuroplasticity, and an attractive approach to support cognitive remediation. Here we provide a systematic review of 26 papers using NIBS to ameliorate cognitive dysfunctions in three prevalent neurodevelopmental disorders: Attention-Deficit/Hyperactivity Disorder (ADHD), Developmental Dyslexia and Developmental Dyscalculia. An overview of the state of research shows a predominance of studies using repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS) techniques, and an unequal distribution among clinical conditions. Regarding the utility of NIBS, the results are promising but also ambiguous. Twenty-three papers reported beneficial effects, but many of these effects were found only once or were only partially replicated and some studies even reported detrimental effects. Furthermore, most studies differed in at least one core aspect, the NIBS applied, the questionnaires and cognitive tests conducted, or the age group investigated, and sample sizes were mostly small. Hence, further studies are needed to rigorously examine the potential of NIBS in the remediation of cognitive functions. Finally, we discuss potential caveats and future directions. We reason that if adequately addressing these challenges NIBS can be feasible, with potential benefits in treating neurodevelopmental disorders.

Reading proficiency influences the effects of transcranial direct current stimulation: Evidence from selective modulation of dorsal and ventral pathways of reading in bilinguals

INTRODUCTION

tDCS can modulate reading which is processed by lexical (ventral) and sub-lexical (dorsal) pathways. Previous research indicates that pathway recruitment in bilinguals depends on a script's orthographic depth and a reader's proficiency with it. The effect of tDCS on each reading pathway has not been investigated in bilinguals. We stimulated the left dorsal and ventral pathways separately in Chinese-English (C-E) bilinguals to understand whether pathway-specific modulation by tDCS is possible and, if so, how it is influenced by orthographic depth and script proficiency.

METHODS

A double-blind, sham-controlled, within-subject experiment was designed wherein 16 balanced bilinguals received anodal tDCS in dorsal, ventral and sham sessions. Two tDCS montages of electrode sizes 5 × 5 cm² with 1) anode at CP5 and cathode at CZ, and 2) anode at TP7 and cathode at nape of the neck, were applied for stimulating the dorsal and ventral pathways respectively. Bilinguals were asked to read word lists for each language before and after stimulation. RTs for accurate trials were analysed using linear mixed-effect modelling that included proficiency scores for reading English pseudo-words (PW) and Chinese pinyin.

RESULTS

For both languages, word reading RTs were faster following dorsal pathway stimulation. The dorsal stimulation effect (change in RT) was negatively correlated with pseudoword reading and pinyin proficiency. Stimulation of the ventral pathway decreased RTs only for Chinese reading.

CONCLUSION

Dorsal and ventral reading pathways can be selectively modulated by tDCS in bilingual readers with dorsal (sub-lexical) pathway stimulation affecting reading in both scripts and ventral (lexical) pathway stimulation selectively affecting Chinese reading. Dorsal pathway tDCS effects are modulated by sub-lexical reading proficiency.

Selective enhancement of low-gamma activity by tACS improves phonemic processing and reading accuracy in dyslexia

The phonological deficit in dyslexia is associated with altered low-gamma oscillatory function in left auditory cortex, but a causal relationship between oscillatory function and phonemic processing has never been established. After confirming a deficit at 30 Hz with electroencephalography (EEG), we applied 20 minutes of transcranial alternating current stimulation (tACS) to transiently restore this activity in adults with dyslexia. The intervention significantly improved phonological processing and reading accuracy as measured immediately after tACS. The effect occurred selectively for a 30-Hz stimulation in the dyslexia group. Importantly, we observed that the focal intervention over the left auditory cortex also decreased 30-Hz activity in the right superior temporal cortex, resulting in reinstating a left dominance for the oscillatory response. These findings establish a causal role of neural oscillations in phonological processing and offer solid neurophysiological grounds for a potential correction of low-gamma anomalies and for alleviating the phonological deficit in dyslexia.

A Study of Null Effects for the Use of Transcranial Direct Current Stimulation (tDCS) in Adults With and Without Reading Impairment

There is evidence to support the hypothesis that the delivery of anodal transcranial direct current stimulation (tDCS) to the left temporoparietal junction can enhance performance on reading speed and reading accuracy (Costanzo et al., 2016b; Heth & Lavidor, 2015). Here, we explored whether we could demonstrate similar effects in adults with and without reading impairments.

METHOD

Adults with (N = 33) and without (N = 29) reading impairment were randomly assigned to anodal or sham stimulation conditions. All individuals underwent a battery of reading assessments pre and post stimulation. The stimulation session involved 15 min of anodal/sham stimulation over the left temporoparietal junction while concurrently completing a computerized nonword segmentation task known to activate the temporoparietal junction.

RESULTS

There were no conclusive findings that anodal stimulation impacted reading performance for skilled or impaired readers.

CONCLUSIONS

While tDCS may provide useful gains on reading performance in the paediatric population, much more work is needed to establish the parameters under which such findings would transfer to adult populations. The documentation, reporting, and interpreting of null effects of tDCS are immensely important to a field that is growing exponentially with much uncertainty.

Educational fMRI: From the Lab to the Classroom

Functional MRI (fMRI) findings hold many potential applications for education, and yet, the translation of fMRI findings to education has not flowed. Here, we address the types of fMRI that could better support applications of neuroscience to the classroom. This 'educational fMRI' comprises eight main challenges: (1) collecting artifact-free fMRI data in school-aged participants and in vulnerable young populations, (2) investigating heterogenous cohorts with wide variability in learning abilities and disabilities, (3) studying the brain under natural and ecological conditions, given that many practical topics of interest for education can be addressed only in ecological contexts, (4) depicting complex age-dependent associations of brain and behaviour with multi-modal imaging, (5) assessing changes in brain function related to developmental trajectories and instructional intervention with longitudinal designs, (6) providing system-level mechanistic explanations of brain function, so that useful individualized predictions about learning can be generated, (7) reporting negative findings, so that resources are not wasted on developing ineffective interventions, and (8) sharing data and creating large-scale longitudinal data repositories to ensure transparency and reproducibility of fMRI findings for education. These issues are of paramount importance to the development of optimal fMRI practices for educational applications.

Non-invasive Brain Stimulation for the Rehabilitation of Children and Adolescents With Neurodevelopmental Disorders: A Systematic Review

In the last years, there has been a growing interest in the application of different non-invasive brain stimulation techniques to induce neuroplasticity and to modulate cognition and behavior in adults. Very recently, different attempts have been made to induce functional plastic changes also in pediatric populations. Importantly, not only sensorimotor processing, but also higher-level functions have been addressed, with the aim to boost rehabilitation in different neurodevelopmental disorders. However, efficacy and safety of using these techniques in pediatric population is still debated. The current article aims to review the non-invasive brain stimulation studies conducted in pediatric populations using Transcranial Magnetic Stimulation or transcranial Direct Current Stimulation. Specifically, the available proofs concerning the efficacy and safety of these techniques on Autism Spectrum Disorder, Attention-deficit/hyperactivity disorder, Dyslexia, Tourette syndrome, and tic disorders are systematically reviewed and discussed. The article also aims to provide an overview about other possible applications of these and other stimulation techniques for rehabilitative purposes in children and adolescents.

Transcranial Direct Current Stimulation in Child and Adolescent Psychiatric Disorders

Research involving transcranial direct current stimulation (tDCS) in child and adolescent psychiatry is limited. Early, short-term studies have found tDCS to be safe and well-tolerated in youth with neurodevelopmental disorders (attention-deficit hyperactivity disorder, autism, learning disorders). Preliminary data suggest potential utility in symptom reduction and improving cognitive function. Further careful research considering implications for the developing brain is necessary.

tDCS Modulatory Effect on Reading Processes: A Review of Studies on Typical Readers and Individuals With Dyslexia

The possibility to use non-invasive brain stimulation to modulate reading performance in individuals with developmental dyslexia (DD) has been recently explored by few empirical investigations. The present systematic review includes nine studies which have employed transcranial direct current stimulation (tDCS) aiming at improving reading abilities in both typical readers and individuals with DD. Anodal tDCS over the left temporo-parietal cortex—a region which is typically involved in phonological and orthographic processing during reading tasks and underactive in individuals with DD—was the most frequently used montage. The majority of studies employing such stimulation protocol showed significant improvement in differential reading subprocesses. More precisely, word decoding was improved in adult readers, whereas non-word and low-frequency word reading in younger individuals. Furthermore, tDCS was found to be specifically effective in poor readers and individuals with DD rather than typical readers, in spite of the specific brain region targeted by the stimulation; Left frontal, left temporo-parietal, and right cerebellar tDCS failed to modulate reading in already proficient readers. Overall, tDCS appears to be a promising remedial tool for reading difficulties, even when applied to younger populations with reading problems. Further empirical evidence is needed to confirm the potential of neuromodulation as a successful intervention method for DD.