Effects of Transcranial Direct Current Stimulation for Enhancing Cognitive Function in Individuals With Autism Spectrum Disorder - A Pilot fMRI Study

For the active-tDCS condition, participants will receive a stimulation on the dorsolateral prefrontal cortex, with ramp up and ramp down mode for 30 seconds, eliciting a tingling sensation on the scalp that fades over seconds.

Participants will receive active-tDCS over 10 sessions in 2 weeks (20 minutes per session, once per day, for 10 consecutive working days), with concurrent computerized cognitive training. The training comprises of 10 games targeting multiple executive functions.

For sham-tDCS condition, participants will receive an initial stimulation of a ramp up and ramp down mode for 30 seconds, eliciting a tingling sensation on the scalp. Then the stimulation will be discontinued.

Participants will receive sham-tDCS over 10 sessions in 2 weeks (20 minutes per session, once per day, for 10 consecutive working days), with concurrent computerized cognitive training. The training comprises of 10 games targeting multiple executive functions.

Derived by summing the scores from the test battery of executive functions. To reduce the number of statistical comparisons, one Executive Composite score will be computed from the different executive function measures. This will be done by converting the raw scores on the different executive function measures to Z scores. The Z scores from the different executive function measures will then be averaged to yield the Executive Composite score. Lower scores indicate poorer executive functioning.

RTI assesses motor and mental response speeds, reaction time, response accuracy and impulsivity. It consists of 30 trials with five potential targets and requires participants to make flexible responses as fast as possible to the target stimulus (shown in yellow). Specifically, movement and reaction time will be measured, where shorter duration reflects faster processing

SWM assess the memory ability of visuospatial information. Participants are required to search the tokens from a number of boxes but not pressing the boxes which tokens have been found. Errors (lower scores indicate lower repetition on pressing the same boxes that token has been found) and strategy (lower scores suggest higher strategy use in begin of choosing the same boxes) will be measured.

MTT assesses the ability to resolve the interference of task-irrelevant information (stroop-like effect). The test displays an arrow which can appear on either the left or right side of the screen and can point to either the left or right side. In each trial, participants are presented with a cue that indicates which button to press according to two different rules. And the rules that participants have to follow may change from trial to trial in a randomized order. Participant's response latencies and error scores will be measured.

ERT assesses the ability to identify six basic emotions in facial expressions along a continuum of expression magnitude. Participants must select which emotion the facial image displayed 0.2s ago. Response latencies and accuracy will be measured.

The VFT assesses an individual's ability of working memory retrieval and executive control by instructing the individual to generate words for given semantic categories within a limited time. Participants will be given one minute for each category, which will be counterbalanced across participants to avoid order effects. The number of unique and correct words generated will be counted for each of the participants.

The FPT assess an individual's design fluency and mental flexibility through instructing the individual to create unique, geometric patterns. Participants will be given a sheet of paper containing an array of 40 identical boxes. Each box contains 5 dots, arranged in the same pattern as '5' on a standard die. Participants have to connect 2 or more of the 5 dots using straight lines to create as many unique designs as possible within 5 minutes. The number of unique and correct patterns generated will be counted for each of the participants at 3 minutes and 5 minutes.

CTT is a test that measures attention, processing speed, and flexibility. In Part 1, participants will connect numbered circles in sequential order as fast as possible. In Part 2, participants will also numbers in order, but must also alternate between circles of two different colors (pink and yellow). The execution time will be measured.

The d2 Test of Attention measures selective and sustained attention, as well as visual information processing. Participants will be given 14 rows with 40 characters each, of which they must scan each row and cross out every target item (the letter 'd' with 2 dashes either above, below, or one in each position). Therefore, participants much ignore distractors along each row (i.e. the letter 'p' with any number of dashes, or 'd' with the wrong number of dashes). The number of errors will be counted for each participant.

SRS-2 is a sensitive measure of social functioning in individuals that detects even subtle symptoms that are highly related to ASD. It uses a four-point scale and focuses on different aspects of socialization. The total score reflects the clinical effectiveness of tDCS, and higher scores indicate greater symptom severity. It has been shown that SRS-2 is sensitive to detect changes in social communication improvement related to improved cognitive functioning after treatment.

The study proposed will examine the biological mediator variable, E/I ratio, to explain the effects of tDCS. MRI data will be collected in the resting-state before and immediately after the 10-session intervention program. Further network analysis will be performed to characterize broader shifts in functional brain connectivity.