Targeting Repetitive Behaviors in Autism Spectrum Disorder Via Transcranial Direct Current Stimulation

The primary outcome measure will be the Total Score of the Repetitive Behavior Scale-Revised (Bodfish, 2000). It consists of a 43-item parent-report questionnaire evaluating the extent of RBs in individuals with ASD. The tool encompasses six scales: Stereotyped Behavior (6 items), Self-injurious Behavior (8 items), Compulsive Behavior (8 items), Routine Behavior (6 items), Sameness Behavior (11 items), and Restricted Behavior (4 items). The items are rated on a four-point scale (0-Behavior does not occur, 1-Behavior occurs and is a mild problem, 2-Behavior occurs and is a moderate problem, 3-Behavior occurs and is a severe problem); an overall total raw score and a total number of items score for each subscale are computed. Higher scores indicate greater severity of repetitive behaviors. The sum of all items provides a total raw score ranging from 0 to 129, with higher scores indicating more severe repetitive behaviors.

The version of the Wisconsin Card Sorting Test for developmental stages evaluates executive functions. The Modified Card Sorting Test (MCST; Nelson, 1976) assesses executive functions in children aged 4-13 years. It requires assigning 48 cards, on which one to four symbols are printed in different colors and shapes. The sorting rule (number, shape, color) changes after six correct assignments. The participant must deduce the current rule from the own pattern of responses. The number of right and wrong assignments and the number of errors will be computed.

The Stop Signal Task is a computerized task evaluating inhibitory control. The task is structured in line with the consensus guide of SST (Verbruggen et al., 2019) and it will be performed on PsychoPy® software (Open Science Tools Ltd., Nottingham, UK). The task duration will be approximately 14 minutes. The Stop Signal Task will yield the following measures: stop signal reaction time, calculated in milliseconds by subtracting a mean Stop Signal Delays from the observed mean reaction times in no-stop trials; go accuracy; go reaction times; Stop Signal Delay.

The Short Sensory Profile 2 (Dunn, 2014) is a parent report questionnaire for evaluating the sensory processing pattern in children aged 3-14 years. It contains 34 items. Scores are assigned on a five-point Likert scale and range from "always = 0" to "often = 1" to "sometimes = 2" to "rarely = 3" to "never = 4". Low scores are indicative of frequent dysfunctional behavior. Based on a bell curve normed distribution, the raw score total for each quadrant can be classified as "much less than others" (lower 2%), "less than others" (between 1 SD and 2 SD below the mean, accounting for 14% of the normative sample), "just like the majority of others" (± 1 SD from the mean and accounting for 68% of the normative sample), "more than others" (between 1 SD and 2 SD above the mean), and "much more than others" (upper 2%).

The Behavior Rating Inventory of Executive Function (Gioia et al., 2015) is a parent report questionnaire consisting of 63 items for an ecological and comprehensive evaluation of executive functions in children aged 5-18 years. The tool encompasses 63 items evaluating inhibition, self-monitoring, shift, initiation, working memory, emotional control, planning, task-monitoring, and organization of materials. Items are further dived into 4 indices as follows: the Behavior Regulation Index, the Emotion Regulation Index, the Cognitive Regulation Index, and the Global Executive Composite. Raw scores of each scale and index are converted into T scores (M = 50, SD = 10) and percentiles. For all clinical scales and indices, T scores from 60 to 64 and from 65 to 69 are considered respectively mildly elevated and potentially clinically elevated while T scores at or above 70 are clinically significant.

The Sleep Disturbance Scale for Children (Bruni et al., 1996) is a parent report questionnaire for evaluating the sleep functioning of children and adolescents aged 6-16 years. The tool investigates the occurrence of sleep disturbances in the previous six months throughout 26 items on a five-point Likert scale (1 = least severe and 5 = most severe). It encompasses the following scales: difficulty in initiating and maintaining sleep, sleep-disordered breathing, disorders of arousal, sleep-wake disorders, disorders of excessive somnolence, and sleep hyperhidrosis. The sum of all items provides a total raw score ranging from 26 to 130, with higher scores indicating more sleep difficulties. A T score of >70 is clinically significant while T scores under 60 or ranged 61-69 are respectively in the average or borderline range.

The Child Behaviour Checklist/ 6-18 (Achenbach and Rescorla, 2001) is a parent report questionnaire to evaluate behavioral and psychopathological symptoms during the preceding 6 months in individuals aged 6-18 years. It includes 113 items on a three-point Likert scale (0 = not true; 1 = somewhat or sometimes true; 2 = very true or often true). According to the cut-off thresholds of Achenbach and Rescorla (2001), T-scores > 69 were classified as clinically relevant, t-scores between 65 and 69 were classified as borderline, and T-scores < 65 indicated non-clinical symptoms. For the internalizing problems, externalizing problems, and total problems scales, T-scores > 63 were classified as clinically relevant, T-scores between 60 and 63 were classified as borderline, and T-scores < 60 indicated non-clinical symptoms.

The Childhood Autism Rating Scale-2 (Schopler et al., 2010) is a rating scale for symptoms related to ASD. Higher scores indicate more severe symptoms of ASD. The instrument is designed for children aged 2-6 years or in individuals with ASD and low functioning (IQ ≤ 79 and regardless the child's age - Standard Form), and individuals with ASD and high functioning (IQ>80 - High Functioning Form). Both versions contain 15 items rated on a 4-point scale with higher scores revealing more severe symptoms related to ASD. The total raw score is converted into standard score within three ASD severity levels: no or minimum symptoms of ASD (15-29.5 or 15-27.5 with >13 years for the standard form; 15-27.5 for the high functioning form) mild to moderate symptoms of ASD (30-30.6 or 28-34.5 with >13 years for the standard form; 28-33.5 for the high functioning form), and moderate to severe symptoms of ASD (>35 or >37 with >13 years for the standard form; >34 for the high functioning form).

The Parenting Stress Index Short Form (Abidin, 1997) is a self-report questionnaire designed to evaluate parental stress levels in parents of children aged 1 month to 12 years. The instrument is used in both clinical and research settings. It contains 36 items rated on a five-point Likert scale (1 = strongly disagree and 5 = strongly agree). Items encompass three subscales as follows, parental distress or the experienced distress in the role of being a parent, difficult child linked to the child's behavioral problems, and parent-child dysfunctional interaction. The sum of all items results in the Total Stress score. The total raw score is converted into percentile score; percentile ≥85 is considered as clinically significant.

Resting-state EEGs will be recorded in a sound-attenuated, electrically shielded room to minimize external noise and interference.