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.


Background and rationale 6a
Description of research question and justification for undertaking the trial, including summary of relevant studies (published and unpublished) examining benefits and harms for each intervention _____ 6b

S2. Checklist adapted from Antal et al. (2017)
A structured checklist increases the reproducibility of studies, minimizes deviations from a given protocol and diminishes variability.A structured checklist is thus the recommended procedure for enhancing reliability and comparability in publications of TES experiments/trials.

1) Participant information
• Age: • Gender: • Handedness: • Head size (distance in cm: inionnasion, ear to ear distance): • Previous experience with TES (additional information of potential relevance): • Medication (Depending on the type of study an even more precise documentation may be necessary, measurement of drug levels may be considered), label and dose: Within last hours

Within last days
Within last months Average with last months (how many months?) • Drugs (e.g.marijuana) consumption (to be specified): (for comparability important that unit is given and comparable measures are noted) • Hormonal/menstrual cycle of female subjects • In case of patients non-neuropsychiatric comorbidities: 2) Procedures applied, Dose parameters (sufficient information about the stimulation parameters should be provided in order to replicate or model the stimulation dose independently based on these parameters) • Type of stimulation (complicated waveforms with drawings): • Metric to be used (e.g., behavioral, cognitive, EEG, MEP, MRI): • Product number and model of stimulator used (consider Nr. as encoded in case of multiple stimulators available): • Stimulation intensity (peak-to-baseline): • Stimulation duration:

Duration of ramping
Fragmented stimulation (interval duration) • Type and number of electrodes: • Electrode positions: • Electrode polarities in case of tDCS: • Position of cable fixation at electrode: • Electrode shape: target electrode: return electrode: • Electrode size: target electrode: return electrode: • Electrode impedance: target electrode: return electrode: • Method of allocation of electrode position (neuronavigation, MEP hot spot, modeling etc.): • Electrode-skin interface (any skin preparation steps): • Type of fixation: saline (molarity?), in case of cream, brand: Other factors to be considered • Tasks/status during stimulation (if any): o Not specified or regulated Specified/regulated: details • Day time of the experiment (fromto): • Attention (level of arousal) 1. before stimulation: 2. during stimulation (optimal results expected with relaxation, not during arousal or sleepiness): 3. after stimulation: 4. Number of hours in sleep during the last night: • Prior motor activity (i.e.cycling before stimulation, if yes, please define the duration): • Prior rest (sleep) before stimulation: • Duration of the whole experiment including preparation: • Number of years in education (of interest in special, e.g. in cognitive studies): • Additional comments

S3. Pilot study of the reading tasks
A behavioural pre-test was administered to 20 typically developing readers (10 children and adolescents: 5 females; M = 12.03 yrs, SD = 1.38 yrs; 10 young adults: 9 females; M = 27.10 yrs, SD = 2.38 yrs).Each participant had to read aloud as rapid and accurate as possible the following reading tasks: -10 texts of approximately 400 syllables in length (TEXT); TEXT was written with Century Schoolbook font, size 13, single-spaced, on a white sheet of A4 paper.HF, LF, NW were arranged in 30-items columns, written with Century Schoolbook font, size 13, single-spaced, on a white sheet of A4 paper.TEXT derived from an Italian novel (Calvino, 1963).
Items in HF list and LF list were matched for Italian written word frequency, number of letters and syllables, bigram frequency (according to CoLFIS, http://www.Istc.cnr.it/material/database/colfis) and mean onset reaction time (Barca et al., 2002).
For each of the four reading tasks (TEXT, HF, LF, and NW), reading accuracy and speed data were collected.
Concerning TEXT reading accuracy, an error point was assigned in presence of substitution, omission, and/or addition of syllables.A 0.5 error was assigned in case of auto-correction during reading.The number of words correctly read was considered, and the percentage of accuracy was calculated via dividing the number of correctly read stimuli by the total number of stimuli presented and multiplying the result by 100.For the remaining tasks (HF, LF, NW), an error point was assigned in presence of substitution, omission, and/or addition of syllables, while auto-corrections during reading was not treated as errors.The number of errors was considered, and the percentage of errors was calculated via dividing the number of errors by the total number of stimuli presented and multiplying the result by 100.
Concerning reading speed, syllables per seconds (syll/s) was considered by dividing the total number of pronounced syllables by the time taken to complete the reading task (in seconds) for all tasks (TEXT, HF, LF, NW).

S3.1. Statistical Analysis
To compare accuracy (percentage of accuracy), analyses of covariance (ANCOVAs) were run for each reading measure (TEXT, HF, LF, and NW) with number of stimuli (10 for TEXT; 9 for HF, 9 for LF, and 9 for NW) as independent factor.The potential effects of age were taken into account by including the participants' age at baseline as a covariate.
The same analyses were used to compare each reading measure on reading speed (syll/sec).
Post-hoc comparisons were run using Tukey's honest significance test.Partial eta square (ηp 2 ) was used as a measure of effect size.

S3.2. Results
Table S1 shows Means (SDs) of reading accuracy (percentage of accuracy) and speed (syll/sec) for each version of the set of stimuli (TEXT, HF, LF, and NW).

S3.3. Conclusions
For LF exclusively, ANCOVA revealed significance in both accuracy and speed.Given the nonsignificant results of post-hoc analyses concerning accuracy, we chose to discard versions based solely on post-hoc analyses of speed.As a result, we excluded lists LF_1 and LF_2.
At the end of the selection process, we rerun the same analysis to confirm the non-significance of the ANCOVA.
Table S1.Means (SDs) of reading accuracy and speed for each version of the tasks (TEXT, HF, LF, and NW).

[]
At the beginning [ ] At approximately in the middle [ ] Towards the end of the stimulation Duration (multiple options allowed) [ ] Only initially [ ] It stopped in the middle of the block [ ] It stopped at the end of the block How much did these sensations affect your general state? to the electrode, (which one?)____________ [ ] Other If you would like to provide more details, please briefly describe the experimented sensations in relation to the "Other" or "Fatigue" or….Response: To be administered at the end of each stimulation session: Do you believe that you received a real or a placebo stimulation?[ ] Real [ ] Placebo [ ] I do not know Investigator:Please report any adverse event/problem that occurred and rate the event/problem on a scale from 0

______ Methods: Data collection, management, and analysis
How personal information about potential and enrolled participants will be collected, shared, and maintained in order to protect confidentiality before, during, and after the trial it is independent from the sponsor and competing interests; and reference to where further details about its charter can be found, if not in the protocol.Alternatively, an explanation of why a DMC is not needed______ 21bDescription of any interim analyses and stopping guidelines, including who will have access to these interim results and make the final decision to terminate the trial ______ Harms 22 Plans for collecting, assessing, reporting, and managing solicited and spontaneously reported adverse events and other unintended effects of trial interventions or trial conduct ______ Auditing 23 Frequency and procedures for auditing trial conduct, if any, and whether the process will be independent from investigators and the sponsor na____________ Ethics and dissemination Research ethics approval 24 Plans for seeking research ethics committee/institutional review board (REC/IRB) approval na____________ Protocol amendments 25 Plans for communicating important protocol modifications (eg, changes to eligibility criteria, outcomes, analyses) to relevant parties (eg, investigators, REC/IRBs, trial participants, trial registries, journals, regulators) ______ Consent or assent 26a Who will obtain informed consent or assent from potential trial participants or authorised surrogates, and how (see Item 32) ______ 26b Additional consent provisions for collection and use of participant data and biological specimens in ancillary studies, if applicable na___________ Confidentiality 27