Exploring response inhibition in adults with attention deficit hyperactivity disorder: An ERP study

The present study used event-related potentials to examine the temporal course of deficient response inhibition associated with adult attention deficit hyperactivity disorder (ADHD), either with (Experiment 2) or without (Experiment 1) the added requirement of interference control. Two experiments recruited different adult ADHD and control groups. A stop task and a choice-reaction task constituted Experiment 1; a stop task and a more difficult flanker task constituted Experiment 2. The study had three main results. First, a consistent ERP pattern of response inhibition was demonstrated across the two experiments during successful inhibition trials, consisting of an earlier N1, greater P2, smaller N2, greater and earlier P3. Second, in both experiments adults with ADHD performed worse than controls in response inhibition, as evidenced by a delayed SSRT. This delay was accompanied by an ERP pattern of poor response inhibition, which consisted of a smaller N1, delayed N2, smaller and delayed P3 in Experiment 1 and of a delayed N1, P2, N2, and P3 in Experiment 2. Third, ADHD adults showed no additional difficulties in response inhibition as interference control was introduced as the primary response execution task. The results showed that response inhibition is revealed at multiple temporal points of processing. Adults with ADHD display inferior inhibitory processing of responses at each of these processing stages. However, their poor response inhibition is not further deteriorated by the added requirement of interference control, a finding that may have important clinical and theoretical implications. The results are consistent with Halperin and Schulz’s (2006) prefrontal compensation hypothesis, which states that symptoms of ADHD result from insults to subcortical regions, with symptom improvement determined by compensation from the prefrontal cortex through neural plasticity