Efficacy of Transcranial Direct Current Stimulation in Developmental Dyslexia: a scoping review

Constantino, Esther; Castro, Isabela Ciola de; Lima, Vânia Lúcia Carvalho de; Avila, Clara Brandão de

doi:10.1590/2317-1782/e20240134en

person Esther Constantino

identification and selection of relevant studies and the data mapping · drafting the manuscript

schoolDepartamento de Fonoaudiologia, Escola Paulista de Medicina – EPM, Universidade Federal de São Paulo – UNIFESP - São Paulo (SP), Brasil.

0000-0002-9919-9106

person Isabela Ciola de Castro

analised the articles · drafting of the work and reviewed it critically · interpretation of data and wrote the manuscript

schoolPrograma de Pós-graduação em Distúrbios da Comunicação Humana, Universidade Federal de São Paulo – UNIFESP - São Paulo (SP), Brasil.

0000-0002-8826-7310

person Vânia Lúcia Carvalho de Lima

co-supervised the work and the writing of the manuscript

schoolPrograma de Pós-graduação em Distúrbios da Comunicação Humana, Universidade Federal de São Paulo – UNIFESP - São Paulo (SP), Brasil.

0000-0001-7947-189X

person Clara Brandão de Avila

work design · supervised the systematic review and made the final approval of the version

schoolDepartamento de Fonoaudiologia, Escola Paulista de Medicina – EPM, Universidade Federal de São Paulo – UNIFESP - São Paulo (SP), Brasil.schoolPrograma de Pós-graduação em Distúrbios da Comunicação Humana, Universidade Federal de São Paulo – UNIFESP - São Paulo (SP), Brasil.

0000-0002-5708-8299

Conflict of interests: nothing to declare.

Correspondence address: Isabela Ciola de Castro Departamento de Fonoaudiologia, Escola Paulista de Medicina – EPM, Universidade Federal de São Paulo – UNIFESP Rua Botucatu, 802, São Paulo (SP), Brasil, CEP: 04023-062. E-mail:
isabela.ciola@hotmail.com

Title	Cortical areas and polarities	Participants	Sessions (number and duration)	Combined intervention	Synopsis of results	Duration of the result
Modulation of auditory temporal processing, speech in noise perception, auditory-verbal memory, and reading efficiency by anodal tDCS in children with Dyslexia(¹⁹)	Assembly (1): Anode-left temporoparietal region; and Cathode-right temporoparietal region. Assembly (2): Anode-left temporoparietal region; and Cathode-right shoulder.	17 children and adolescents	05 sessions, with a one-week interval between them (2 sessions in each assembly and 1 Sham session)	No intervention Combined	- Significant effect on temporal resolution, speech perception, and auditory verbal memory tasks in the two active assemblies, speed and accuracy of texts, low-frequency words, and pseudowords compared to Sham and initial assessment. - Assembly (2) resulted in better temporal resolution, speech perception, and auditory memory outcomes than assembly (1). - There was no difference in reading high-frequency words.	- Effect observed immediately after stimulation.
Effects of a short and intensive transcranial direct current stimulation treatment in children and adolescents with developmental Dyslexia: A crossover clinical trial(²⁰)	Anode-between the left occipitotemporal and left temporoparietal regions; and Cathode-between the right occipitotemporal and right temporoparietal regions.	24 children and adolescents	05 consecutive sessions for 20 minutes.	- Word reading (high and low frequency), pseudowords, and text. - Cognitive-linguistic stimulation: operational phonological memory, combining phonemes, rapid automatic naming.	- Only in the active group: Positive effect on pseudoword reading speed, phonological working memory, and phoneme combination. - No effect on reading speed of low and high-frequency words and reading accuracy of text, high and low-frequency words, and pseudowords.	- Effect observed immediately after and one month after stimulation.
Reading and phonological awareness improvement accomplished by transcranial direct current stimulation combined with phonological awareness training: A randomized controlled trial(²¹)	Anode-temporoparietal junction; and Right cathode-temporoparietal junction. Sham	28 children and adolescents	15 sessions: 3 weekly sessions of 60 minutes each.	Cognitive-linguistic and reading training: “Gillon Phonological Awareness Training Programme”	- Positive effect on reading low- and high-frequency words and non-words for the Active and Sham groups from the 5^th session.	- Effect observed after the 5^th, 10^th, and 15^th sessions and 6 weeks later (follow-up).
					- Positive effect on reading non-words for Active from the 5^th and the 10^th for Sham.
					- Active better at reading non-words from the 10^th session, immediately after, and at follow-up.
					- Positive effect for Active in rhyme detection, from the 5^th session and at the end of the intervention and follow-up for Sham.
					- Difference between groups: Active better at the end of the intervention, with maintenance at follow-up.
					- Group effect for phoneme exclusion: Active better performance at the 5^th session; positive effect on Sham at the end and follow-up. No difference between groups.
Beyond Reading Modulation: Temporo-Parietal tDCS Alters Visuo-Spatial Attention and Motion Perception in Dyslexia(²²)	Assembly (1): Anode-left temporoparietal region; and Cathode-right contralateral region. Assembly (2): Anode-right temporoparietal region; and Cathode-left contralateral region.	10 children and adolescents	Two sessions, each lasting 20 minutes, and different setups, with a minimum 24-hour interval between them.	No intervention Combined	- Positive effect on accuracy for the Group with assembly (1) in text reading.	- Effects seen immediately after stimulation.
					- Smaller positive effect and mean reaction time for the Group with assembly (1) on lexical decision tasks
					- No significant difference in reading speed and accuracy of low-frequency, high-frequency, and non-words.
					- No difference in phoneme matching tasks, working memory, and quick naming.
					- Positive effects for assembly (1) with greater perception of movement and reduced visual-spatial attentional focus.
					- The main effect of stimulation on assembly (1) is more significant than in Group with assembly (2).
Effects of a short, intensive, multi-session tDCS treatment in developmental dyslexia: Preliminary results of a sham-controlled randomized clinical trial(²³)	Anode- parietal-occipital regions P7. Cathode- – contralateral region (P8)	27 children and adolescents distributed in Active and Sham groups Cross-over.	05 consecutive sessions for 20 minutes.	No intervention Combined	- Positive effect in the active group regarding the reading speed of non-words immediately after and 1 week after the end of treatment compared to baseline.	- Effects observed before, immediately after and 01 week after treatment.
Individual Differences Modulate the Effects of ETCC on Reading in Children and Adolescents with Dyslexia(²⁴)	Anode-between the temporoparietal and left parietal regions; and Cathode-between the temporal and parietal regions on the right. Sham	26 children and adolescents distributed in Active and Sham groups	Eighteen sessions: 3 20-minute weekly sessions for 6 weeks and a minimum 48-hour interval between sessions.	Word reading training with acceleration and spelling.	- Positive effect regarding group, time, and word reading speed.	- Effects observed immediately after, one month after, and six months after.
				Word reading training with acceleration and spelling.	- Individual differences between participants of the Active group; less fluent and older subjects displayed a more significant change in word reading fluency at each time point than younger subjects.
Long-lasting improvement following ETCC treatment combined with training for reading in children and adolescents with Dyslexia(²⁵)	Anode-between the temporoparietal and left parietal regions; and Cathode-between the temporal and parietal regions on the right. Sham	26 children and adolescents distributed in Active and Sham groups	Eighteen sessions: 3 20-minute weekly sessions for 6 weeks, with a minimum 48-hour interval between sessions.	Fast word reading (Tachistoscopic presentation) Cognitive training: phoneme-grapheme association(²⁶)	- Active Group with a positive effect on the reading of low-frequency words one month after stimulation and pseudowords immediately one and six months after stimulation.	- Effects observed immediately after, one month after, and six months after.
					- Active Group with better performance in reading low-frequency words and pseudowords.
					- Reading efficiency increased after 6 months in the stimulated group.
Impact of Transcranial Direct Current Stimulation on Reading Skills of Children and Adolescents With Dyslexia(²⁷)	Anode-left middle posterior temporoparietal region; and Cathode-right supraorbital region (FP2).	12 children and adolescents	5 consecutive days of stimulation of 30 minutes each session	No intervention Combined	- Positive effect on pseudoword and text accuracy.	- Effect observed after the 5^th session.
		12 children and adolescents		No intervention Combined	- There was no change in the number of correct letters, syllables, words, and reading time.	- Effect observed after the 5^th session.
Evidence for reading improvement following ETCC treatment in children and adolescents with Dyslexia(²⁶)	Anode-between the temporoparietal and left parietal regions; and Cathode-between the temporal and parietal regions on the right. Sham	18 children and adolescents	18 sessions: 3 20-minute weekly sessions for 6 weeks	Fast word reading (Tachistoscopic presentation) Cognitive training: phoneme-grapheme association.	- Positive effect with decreased reading time of low-frequency words and pseudowords immediately and 1 month after the stimulation sessions.	- Effect observed immediately after and 1 month after the stimulation.
		18 children and adolescents	18 sessions: 3 20-minute weekly sessions for 6 weeks		- Reduction of errors of immediate effect and 1 month after the stimulation.
Reading changes in children and adolescents with Dyslexia after transcranial direct current stimulation(²⁸)	Assembly (1): Anode-left temporoparietal region; and Cathode-between the temporal and right parietal region. Assembly (2) Anode-right temporoparietal region; and Cathode-left temporoparietal region. Sham	19 children	One session with pre-evaluation, 20 minutes of stimulation, and post-evaluation carried out sequentially.	No intervention combined	- Positive effect with a difference between groups with assembly (1) in the improvement of text reading accuracy, phoneme combination time, and N-back verbal task.	- Effect observed 20 minutes after stimulation.
Improved reading measures in adults with Dyslexia following transcranial direct current stimulation treatment(¹¹)	Anode-region of the left visual cortex (V5); and Cathode-region of the right orbitofrontal cortex. Sham	19 adults	5 sessions spread over 2 weeks (they did not mention defined intervals between them)	No intervention combined	- Positive effect with a difference between groups in reading speed and the RAN test of numbers and letter naming.	- Effects observed immediately after the 5^th session.