Domain-specific Involvement of the Right Posterior Parietal Cortex in Attention Network and Attentional Control of ADHD: A Randomized, Cross-over, Sham-controlled tDCS Study

Transcranial direct current stimulation (tDCS) has been increasingly used in attention-deficit hyperactivity disorder (ADHD) with mixed results. Previous tDCS studies merely targeted the dorsolateral prefrontal cortex and right inferior frontal gyrus with partial or no improving effects on cognitive deficits respectively. Posterior parietal cortex is another region involved in attentional functioning of ADHD, however, its contribution to ADHD attention functions has not been explored in tDCS studies. Moreover, attention networks are not investigated in the previous tDCS studies in ADHD neither. Here, we explored the effects of anodal tDCS over the right posterior parietal cortex (r-PPC) on attentional functioning (i.e., attention networks, selective attention, shifting attention) and response inhibition in ADHD children. 19 children with ADHD were recruited and underwent anodal/sham r-PPC tDCS (1 mA, 20 min) during task performance in a randomized cross-over design. Our results show an improving effect of anodal r-PPC tDCS specifically on the orienting but alerting or executive networks, in line with findings of healthy populations. Furthermore, activation of the r-PPC had a deteriorating effect on the top-down attentional control required for selective attention measured by the Stroop test. Modeling of the current flow showed a stronger electrical field induced in the inferior PPC (BA 39,40) which mediates bottom-up attentional control. No significant effect on shifting attention and response inhibition was found. Our findings indicate a domain-specific involvement of the r-PPC in attention orienting network of ADHD children. Activation of the r-PPC improves bottom-up but hinders top-down attentional control suggesting a critical role of the r-PPC in ADHD bottom-up attentional control.