The effects of co-occurring ADHD symptoms on electrophysiological correlates of cognitive control in young people with Tourette syndrome

Efficient cognitive control is implicated in tic control in young people with Tourette syndrome (TS). Attention-deficit/hyperactivity disorder (ADHD) frequently co-occurs with TS and is associated with impaired cognitive control. Young people with TS and ADHD (TS+ADHD) show poorer cognitive control performance than those with TS, but how co-occurring ADHD affects underlying neural activity is unknown. We investigated this issue by examining behavioural and event-related potential (ERP) correlates of cognitive control in young people with these conditions. Participants aged 9-17 with TS (n=17), TS+ADHD (n=17), ADHD (n=11), and unaffected controls (n=20) performed a visual Go/Nogo task during electroencephalography (EEG) recording. Behavioural performance measures (D-prime, RT, reaction time variability, post-error slowing) and ERP measures (N2, P3, error-related negativity (ERN), error positivity (Pe)) were analysed in a 2 (TS-yes, TS-no) x 2 (ADHD-yes, ADHD-no) factorial analysis to investigate the effects of TS, ADHD, and their interaction. The results of these analyses showed that ADHD was associated with poorer performance and reduced amplitude of all ERPs, reflecting widespread cognitive control impairments. Tourette syndrome was associated with slowed RTs, which might reflect a compensatory slowing of motor output to facilitate tic control. There was no interaction between the TS and ADHD factors for any behavioural or ERP measure, indicating the impairing effects of ADHD on behaviour and electrophysiological markers of cognitive control were present in TS+ADHD and that RT slowing associated with TS was unaffected by co-occurring ADHD symptoms.