Transcranial direct current stimulation enhances social functioning in autism spectrum disorder

A two-armed, double-blind, sham-controlled trial conducted by researchers at the Hong Kong Polytechnic University and the Chinese University of Hong Kong has demonstrated that transcranial direct current stimulation (tDCS) significantly enhances social functioning in individuals with autism spectrum disorder (ASD), when delivered concurrently with a computerized cognitive remediation training programme.

Approximately 45 percent of individuals with ASD who do not have intellectual disabilities show marked impairment in essential skills for successful social interactions, including recognizing emotions and attributing social meanings, despite having average verbal and performance skills. [Psychol Med 2011;41:619-627; Res Autism Spectr Disord 2013;7:9-16; Res Autism Spectr Disord 2008;2:353-361] Although the exact neurophysiological mechanism remains unclear, it has been suggested that treatments that can address an excitation-inhibition (E:I) imbalance in local neural networks of ASD individuals could promote cognitive flexibility and social communication. [Mol Psychiatr 2019;24:1248-1257]

tDCS is a noninvasive neuromodulation modality that influences cortical excitability by promoting subthreshold changes in resting membrane potentials of the targeted neuronal population. [J ECT 2018;34:144-152; Clin Neurophysiol 2016;127:3425-3454] Study participants in the active tDCS group received a dose of 1.5 mA tDCS over a course of 20 minutes, 5 days per week, for 2 weeks. During tDCS, participants engaged in concurrent app-based cognitive remediation training, which addressed interference control, planning, set shifting, and working memory. Individuals undergoing sham tDCS received the same cognitive remediation training and underwent the same tDCS protocol, except actual stimulation. [Brain Stimul 2022;15:414-425]

The Social Responsiveness Scale – 2nd Edition (SRS-2) results from 41 participants (age, 14–21 years) indicated that multisession prefrontal tDCS significantly enhanced the social functioning of ASD individuals compared with sham tDCS (p=0.03). This improvement was associated with enhanced emotion recognition (p=0.006) and cognitive flexibility (p=0.033). Specifically, the tDCS protocol optimized information processing efficiency (p=0.042), and the optimization showed an association trend with enhanced resting-state functional connectivity in the right medial prefrontal cortex.

“Neurophysiological studies have shown that the heightened E:I ratio in ASD is specifically found in the left dorsolateral and the ventromedial prefrontal cortices [dlPFC and vmPFC], and that this ratio can be modified by repeated inhibitory transcranial magnetic stimulation. Given that the higher E:I ratio in the left dlPFC and right vmPFC in ASD are possibly due to higher glutamate and lower GABA concentrations, respectively, we hypothesized [and subsequently proved] that tDCS with left dlPFC cathode and right supraorbital region anode placement would enhance cognitive and emotional recognition,” explained the researchers. [Acta Paediatr 2015;104:346-355; Front Syst Neurosci 2018;12:20; Brain Sci 2020;10:423]

While significantly more participants in the active vs sham tDCS group experienced short-term itchiness over the stimulation site, the itchiness resolved within 10 minutes after each treatment session. Other side effects were not significantly different between groups.

“The results from this double-blind randomized clinical trial indicate that our tDCS protocol is a safe and efficacious treatment for adolescents and young adults with ASD, which can promote their overall social functioning through enhancing functional connectivity of the right medial PFC – a major hub for flexible social information processing,” concluded the researchers.