Brain Stimulation | 2021
Anodal HD-tDCS for cognitive inflexibility in autism spectrum disorder: A pilot study
Abstract
Cognitive inflexibility is thought to contribute to the core symptom of restricted and repetitive behaviour and interests (RRBI) in autism spectrum disorder (ASD) [1]. The ventrolateral prefrontal cortex (vlPFC) has been strongly implicated in cognitive flexibility. Reduced activation of the vlPFC in ASD has been linked with impaired stimulus valuation and rule acquisition aspects of cognitive flexibility [2,3]. The vlPFC appears a promising target for non-invasive brain stimulation (NIBS) in ASD, raising the prospect of a new therapeutic intervention that could ameliorate cognitive flexibility difficulties in people with ASD. Preliminary studies of transcranial direct current stimulation (tDCS) in ASD have demonstrated short-term improvements in ASD symptomatology, cognitive function, and motor ability [4,5]. To this end, we conducted a pilot study that compared the effects of active and sham (placebo) anodal high-definition transcranial direct current stimulation (aHD-tDCS) over the right vlPFC in adolescents and young adults diagnosed with DSM-5 ASD. Outcome measures included four indices of cognitive flexibility (behavioural, electrophysiological, cognitive, and clinical). We also assessed safety and tolerability of aHD-tDCS in ASD. This was a randomised, sham-controlled, double-blind, crossover clinical trial (see Supplementary Materials, 1.2). aHD-tDCS, generally thought to increase cortical excitability, was administered at 1.693mA for 20 minutes over the right vlPFC on four consecutive days (see Fig. 1). Participants underwent both active and sham aHD-tDCS, with a three-week interval between conditions. The final sample included twelve participants with ASD (7 Males, mean age 1⁄4 25.08 years [SD 1⁄4 7.20]; see Supplementary Materials, 1.1). Ten participants completed both aHD-tDCS conditions. Two participants only completed active aHD-DCS (withdrawing prior to the second randomised condition due to travel difficulties and transportation time). This study was approved by the Human Research Ethics Committee of Deakin University (Melbourne, Australia) and prospectively registered on the Australian New Zealand Clinical Trial Registry (ANZCTR) (ACTRN12616001045404). aHD-tDCSwas administered using awireless (Bluetooth) Neuroelectrics Star Stim control box (HD-tDCS device) and corresponding NIC2 software. The aHD-tDCS montage design, intensity, and electrode positioning over the right vlPFC was derived by Neuroelectrics (See Supplementary Materials, 1.3). During the administration of aHD-tDCS, participants also completed the Stop Task, which engages vlPFC, in an attempt to produce stronger, longer-lasting effects of stimulation [6] (see Supplementary Materials, 1.4).