Transcranial Direct Current Stimulation in Autism Spectrum Disorder

Background: Transcranial Direct Current Stimulation (tDCS) is a form of non-invasive brain stimulation that has aroused increased interests in the past decade. Not only that it is transient with little side-effects, and can be well-tolerated by children, it is also affordable and readily accessible, making it an appealing treatment option for autism spectrum disorder (ASD). Objective: (1) To assess the therapeutic effects of tDCS when combined with cognitive training for 10 consecutive weekdays on improving cognitive processing in adolescents with ASD, relative to control group receiving sham-stimulation, and (2) to evaluate the associated neural mechanisms underlying the treatment effect of tDCS on adolescents with ASD. Methods: 105 adolescents with ASD will be randomly assigned to active- (n=35), sham- (n=35) tDCS, or no-treatment control (n=35) groups. Twenty minute sessions of 1 mA cathodal stimulation to the left dorsolateral prefrontal cortex (DLPRC) in conjunction with cognitive training exercise will be provided on 10 consecutive weekdays. EEGs, functional near-infrared spectroscopy, and neuropsychological tests will be administered before, 1 day and 6 months after the series of tDCS sessions. Hypothesis: We hypothesized that cathodal (inhibitory) tDCS over the left DLPRC will induce (1) stimulation-linked facilitation of learning and enhanced processing speed and resultant improvement of cognitive functioning, in executive function, relative to the sham-tDCS and the wait-list controls, (2) active-tDCS, but not sham-tDCS and wait-list controls, will modulate the intra- and inter-hemispheric neural connectivity, indexed by altered level EEG theta coherence and aberrant fNIRS haemodynamic measures, across brain areas implicated in executive functioning.