Anne Fleur Kortekaas-Rijlaarsdam

CHAPTER 5 100 TD group were included if they had no (parent reported) psychiatric or neurological disorder, including ADHD. To ensure the absence of ADHD, children in the TD group were required to obtain scores ≤ 90 th percentile on both the Inattentive and Hyperactive/ Impulsive scale of the parent version of the DBDRS. TD children were excluded if reported to have ever been diagnosed with a psychiatric disorder (parental report). Two children in the ADHD group did not complete the trial due to adverse events unrelated to the intervention, resulting in 63 participants with ADHD completing the trial. Medication Design and Procedure For the participants with ADHD, a randomized double-blind placebo-controlled crossover design was used to compare the direct effects of extended release MPH (Equasym XL®) with placebo. For details of the trial design, see Kortekaas-Rijlaarsdam et al. (2017b). The current study has been carried out in accordance with the Declaration of Helsinki and was approved by the local ethics committee. Informed consent was obtained from parents and children above the age of 11. Testing was done at the child’s school. All measures were collected by the researchers using fully standardized instructions. All researchers were blinded to medication condition. Testing of children with ADHD (placebo and MPH condition) occurred during expected plasma peak levels of methylphenidate, with testing commencing within 60-90 minutes after medication intake (Banaschewski et al., 2006). The TD group was assessed only once. Testing procedures were identical in the ADHD and TD group, with the exception that the testing of the TD group was preceded by a short version of the WISC-III to estimate TD children’s IQ as TD children were first seen on the day of the assessment. Participants with ADHD received a small gift independent of performance. Task duration varied between subjects, depending on the number of practice block needed (see below). On average, task duration was 10 to 15 minutes. Materials Instrumental learning as well as reversal learning was measured using an adapted child-friendly version of the extensively validated associative learning test (Frank et al., 2004), which has been used in typically developing children and clinical child samples (Königs et al., 2016; Van Den Bos, Crone, & Güroglu, 2012). During the learning phase participants had to choose the stimulus that was associated with the highest reward rate. In the test phase participants were instructed to apply this knowledge to novel stimulus pair combinations (see Figure 5.1). After the test phase, the stimulus-reward associations were reversed within a stimulus pair. Trials in all