In children with attention‐deficit/hyperactivity disorder, less task‐related up‐modulation of motor cortex during response inhibition

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AbstractObjectiveThe aim of this study was to identify a quantitative, brain‐based measure reflecting impaired response inhibition in children with attention‐deficit/hyperactivity disorder (ADHD).MethodsIn this cross‐sectional study, we used transcranial magnetic stimulation (TMS) to evoke potentials in hand muscle during both a simple reaction time and a response inhibition task in 8‐to‐12‐year‐old children, 41 with ADHD (42% girls, 76% white, mean age 10.3 years) and 38 typically developing controls (53% girls, 74% white, mean age 9.8 years). We used mixed‐model linear regressions of evoked potential amplitudes to compare motor cortex excitability at (1) task‐onset (“START”: 550 ms prior to action); (2) preparing‐to‐go (“GO”: 150 ms prior to action); and (3) selecting‐to‐stop (“STOP”: 150 ms after stop cue). We hypothesized that task‐related up‐modulation of motor cortex excitability (motor evoked potential amplitudes) would depend both on task (STOP > GO > START) and on diagnosis (controls > patients).ResultsMotor cortex up‐modulation was significantly greater for STOP trials than during GO or START. Children with ADHD had both worse response inhibition performance (longer stop‐signal reaction times) and significantly less task effect on motor cortex up‐modulation. The largest diagnostic difference in motor cortex activation occurred during STOP trials. Reduced up‐modulation during stopping was also associated with higher parent‐rated symptom severity.InterpretationOur findings suggest that motor cortex up‐modulation of excitability, assessed indirectly by TMS motor evoked potentials, reflects the cognitive load during response inhibition tasks and may be a quantitative, brain‐based indicator of impaired response inhibition in children with ADHD.