Sleep restores daytime deficits in procedural memory in children with attention-deficit/hyperactivity disorder

Sleep supports the consolidation of declarative and procedural memory. While prefrontal cortex (PFC) activity supports the consolidation of declarative memory during sleep, opposite effects of PFC activity are reported with respect to the consolidation of procedural memory during sleep. Patients with attention-deficit/hyperactivity disorder (ADHD) are characterised by a prefrontal hypoactivity. Therefore, we hypothesised that children with ADHD benefit from sleep with respect to procedural memory more than healthy children. Sixteen children with ADHD and 16 healthy controls (aged 9-12) participated in this study. A modification of the serial-reaction-time task was conducted. In the sleep condition, learning took place in the evening and retrieval after a night of sleep, whereas in the wake condition learning took place in the morning and retrieval in the evening without sleep. Children with ADHD showed an improvement in motor skills after sleep compared to the wake condition. Sleep-associated gain in reaction times was positively correlated with the amount of sleep stage 4 and REM-density in ADHD. As expected, sleep did not benefit motor performance in the group of healthy children. These data suggest that sleep in ADHD normalizes deficits in procedural memory observed during daytime. It is discussed whether in patients with ADHD attenuated prefrontal control enables sleep-dependent gains in motor skills by reducing the competitive interference between explicit and implicit components within a motor task.