Effect of modified-release methylphenidate on cognition in children with ADHD: evidence from a temporal preparation task

ADHD is associated with various cognitive deficits, including general performance decrements and specific impairments, for instance in temporal processing. However, time preparation under uncertain conditions has been under-investigated in this population. We aimed at filling this gap. We administered a variable foreperiod paradigm to children with ADHD before and after a one-month treatment with modified-release methylphenidate. Age-matched ADHD children with no treatment and healthy children were also tested as control groups with the same time-schedule. Children with ADHD had general performance deficits (longer and more variable response times), which disappeared in the experimental group after pharmacological intervention. Moreover, ADHD children showed a marked dependency on sequential foreperiod effects (i.e., slower responses for longer preceding foreperiods), especially at short current foreperiods, which were not modulated by the pharmacological treatment. In conclusion, the present findings show that methylphenidate enhances general motor processes rather than more specific time preparation processes, some of which appear deviant in ADHD.