Anne Fleur Kortekaas-Rijlaarsdam

CHAPTER 1 18 This thesis is composed of three parts: (meta-analysis ( part I ), RCT ( part II ) and experimental studies ( part III )). In part I we aggregated and quantified previous research on the immediate effects of MPH on academic accuracy and productivity for different core academic subjects ( 1 st aim of this thesis ) using meta-analysis ( Chapter 2 ). In this chapter we pooled the results from 34 studies 34 studies published between 1980 and 2017. Further, this chapter presents an exploration of the mediating effects of improvements in ADHD symptoms on MPH-related effects on academic performance in ADHD ( 2 nd aim of this thesis ) and the possible moderating effects of demographic and disorder related variables (e.g. age, ADHD severity) and study characteristics (e.g. dosage, study duration). Part II of this thesis aims to add to existing literature by investigating the impact of MPH on academic performance in children with ADHD using a randomized double- blind placebo-controlled cross-over design assessing MPH-effects on well validated and reliable academic outcomes ( 1 st aim of this thesis ). Moreover, the studies described in this part aim to elucidate the mechanisms behind the direct effects of MPH on academic performance ( 2 nd aim of this thesis ). Chapter 3 describes a comparison between ADHD and TD groups in performance on math, reading and spelling tasks and the direct effects of MPH on these academic measures in the ADHD group. In addition, this chapter investigates the possible mediating effect of parent-rated ADHD symptom reductions on MPH-related improvements in academic performance. Furthermore the possible moderating effect of mathematical ability on the effects of MPH on academic performance were studied. Chapter 4 extends these findings by exploring the possible mediating role of MPH-related improvements in cognitive functioning, academic motivation (intrinsic and extrinsic) and perceived academic competence on the effects of MPH on math performance. Figure 1.2 further specifies the model proposed in Figure 1.1 and depicts the expected mediating effects. Part III of this thesis comprises two experimental studies investigating the impact of motivation and MPH on feedback learning and math performance ( 3 rd aim of this thesis ): Chapter 5 describes effects of MPH on the ability to learn novel stimulus- reward associations in children with ADHD and controls, to generalize this knowledge to novel stimulus-pairs and the ability to adjust performance to changes in reinforcement schedule (reversal learning), using a reinforcement learning task. Chapter 6 describes a study further investigating motivated learning in a more academic context. This chapter describes the interaction between MPH treatment and motivational strategies (the effect of positive feedback and reward) on math performance in children with ADHD. Secondly, this chapter describes the validation of a newly developed math task