Transcranial direct current stimulation enhances effort maintenance in ADHD

Background: Youth with attention-deficit/hyperactivity disorder (ADHD) exhibit increased effort aversion, likely due to deficits in anticipatory dopamine firing. Previous research has shown that transcranial direct current stimulation (tDCS) targeting the right prefrontal cortex can enhance activity in dopaminergic meso-striatal regions. However, the extent to which this specific tDCS configuration effectively modulates effort behavior in anticipation of rewards in ADHD remains uncertain. Hypothesis: We expected an increase of effort maintenance and invigoration during and following our tDCS set-up compared to sham in subjects with ADHD. Methods: Twenty-four children and adolescents with ADHD (mean age: 11.6 years; 95% CI [10.7, 12.4]) received 2 mA and sham tDCS for 20 min each. The anode was positioned over the ventromedial prefrontal cortex (PFC), while the cathode was placed over the right dorsolateral PFC, generating an electrical field with maximal strength in the right PFC. During and after the tDCS sessions, participants performed a button-pressing task aimed at earning delayed monetary rewards. Primary outcomes were effort maintenance (frequency of button presses) and invigoration (slopes of button presses), measuring motor task performance. Results: We observed a significant increase in effort maintenance both during (b = 2.66; p < 0.001) and after tDCS (b = 2.04; p= .007) compared to sham. No significant difference was found for invigoration during stimulation, while after bonferroni correction (p = 0.025) a non-significant decrease was found after tDCS compared to sham (b =-5.18; p = 0.041). Conclusion: tDCS targeting the ventromedial PFC (anodal) and right dorsolateral PFC (cathodal) increases effort maintenance in children and adolescents with ADHD.