The dynamics of bimanual coordination in attention deficit hyperactivity disorder

The present research examined how the inhibitory dysfunction observed in Attention Deficit Hyperactivity Disorder (ADHD) affects bimanual coordination in three experiments with unmedicated boys (aged 8 to 15) with ADHD-C (with and without Developmental Coordination Disorder (DCD)) and matched controls. Experiment 1 (N = 31, Mean age = 11 years : 9 months) explored the dynamics of bimanual circling using both free-hand movements using circle templates and constrained movements using cranks. Impairment in temporal stability was mostly attributable to difficulties in controlling the spatial component of the task, which was more pronounced in children with comorbid DCD. Experiment 2 (N = 32, Mean age = 12 years : 1 month) used a Stop-re-engagement paradigm (Change task) with a continuous (hand-circling) task to investigate whether inhibitory deficits at the central level of processing and/or allocation of effort in ADHD affect movement coordination. The ADHD and ADHD/DCD groups showed a lack of inhibitory control, as measured by Switch reaction time. However, these children also displayed slower and more variable speed of execution and the apparent inhibitory deficit was more associated with the reengagement component of the task. Experiment 3 (N = 32, Mean age = 12 years : 1 month) used the Change Task, as traditionally delivered by computer, to investigate the source of the poor response re-engagement. Results showed a slow mode of information processing in ADHD groups rather than a deficit in the processes necessary to inhibit a prepotent xii response. Processing speed was most impaired in children with ADHD/DCD, indicating that difficulties in cognitive flexibility and motor coordination were the main deficits. The overall results are a better fit for the hypothesis that ADHD involves a deficit in the regulation of energetic states. It was concluded that children with ADHD without DCD do not suffer from bimanual coordination impairment and that it is a necessity for future bimanual coordination studies to control for the presence of comorbid DCD in ADHD samples.