Confirmation of an inhibitory control deficit in attention-deficit/hyperactivity disorder

The objective of this study was to determine whether deficient inhibitory c ontrol distinguishes children with a diagnosis of attention-deficit/hyperac tivity (ADHD) disorder, conduct disorder (CD), and comorbid ADHD + CD from normally developing children, Participants were rigorously diagnosed childr en (age 7 to 12 years) with ADHD (N = 72), CD (N = 13) or ADHD + CD (N = 47 ) and 33 control children (NC). We studied inhibitory control using the sto p-signal paradigm, a laboratory task that assessed the ability to inhibit a n ongoing action. The ADHD group had significantly impaired inhibitory cont rol compared to NC, CD, and ADHD + CD children. These results indicate that children with ADHD have deficient inhibition as measured in the stop-signa l paradigm and that ADHD occurring in the presence of ADHD + CD may represe nt a phenocopy of CD rather than a variant of ADHD.