Modulating Attentional Biases of Adults with Autistic Traits Using Transcranial Direct Current Stimulation: A Pilot Study

Background: Pseudoneglect is the propensity for neurotypical individuals to over-attend to the left-side of centrally-presented visual stimuli and is driven by relatively greater lateralization of spatial attention to the right hemisphere (RH) than the left. However, this attentional bias appears to be reduced or absent for individuals with autism spectrum conditions relative to healthy controls, and for neurotypical individuals with high levels of autistic-like traits (ALT) relative to those with low levels of ALT. This reduced bias likely reflects a reduction in the lateralization of spatial attention to the RH for these individuals.

Objectives: The aim of the present study was to determine whether non-invasive transcranial direct current stimulation (tDCS) delivered to the right posterior parietal cortex (PPC) could alter attentional biases in High ALT individuals, such that attentional bias is relatively more comparable to that reported in Low ALT individuals. If tDCS does influence attentional biases in High ALT individuals, this would 1) provide evidence for reduced RH lateralization for spatial attention in High ALT individuals; and 2) indicate that attentional biases, and therefore relative levels of hemispheric activation, are not resistant to modulation via external stimulation.

Methods: The Autism Spectrum Quotient (AQ) was administered to an undergraduate student cohort (n=702), and 38 students invited to participate in the study from the initial pool. Students were categorized as Low ALT (n=18) or High ALT (n=16) if their Autism Spectrum Quotient scores fell below or above the median AQ score for the entire cohort (Median AQ = 107). In separate sessions, participants received approximately 10 minutes of anodal, cathodal, and sham tDCS, while completing the greyscales task – a task that provides an index of attentional lateralization.

Results: The main outcome of the study was that tDCS over the right PPC was particularly effective at modulating attention biases in our High ALT group, but ineffective at inducing attentional changes in the Low ALT group. Critically, a repeated measures ANOVA found an interaction between ALT Group and Stimulation Type, F(2,34)=7.00, p<0.01. Follow-up tests revealed a significant increase in leftward bias as a result of anodal tDCS relative to sham levels in the High ALT group, t(15)=4.09, p<0.001, while no such change was evident in the Low ALT group, t(17)=0.58, p=0.57. The effect of cathodal tDCS on attentional biases was substantially weaker, with the High ALT group falling just short of significant levels, t(15)=2.05, p=0.06 and Low ALT group showing no effect of stimulation, t(17)=0.95, p=0.35.

Conclusions: This study has shown that relatively lower levels of pseudoneglect expressed by High ALT individuals can be increased to a level that is more comparable to what is seen in Low ALT individuals. This finding is important as it suggests that if attention can be modulated using tools like tDCS, other aspects of attention relevant to autism (i.e. global processing, face processing) that are also linked to relative levels of hemispheric activation might also stand to benefit from similar techniques.