Anne Fleur Kortekaas-Rijlaarsdam

CHAPTER 1 16 Mechanism behind MPH-related Improvements in Academic Performance To better understand how and why MPH improves academic performance, and why it’s effects may be very specific (e.g. more evidence for MPH-related improvements in productivity compared to accuracy), it is important to study the mechanism behind these improvements. For example, improvements in academic productivity are often accompanied by large teacher-rated improvements in classroom behavior (Baweja, Mattison, & Waxmonsky, 2015). It is likely that these behavioral improvements partly mediate the positive effects of MPH on academic performance. However, only one study reported on a mediating effect of on-task behavior on the relationship between MPH and academic performance (Froehlich et al., 2014). Yet, it is likely that besides on-task behavior, other MPH-related behavioral improvements mediate the effects of this stimulant on academic performance. Further, MPH positively affects the cognitive abilities of children with ADHD, with small to medium effect sizes for working memory and response inhibition and large effect sizes for attentional measures (Coghill et al., 2014; Pietrzak et al., 2006), all abilities on which subgroups of children with ADHD show deficits (Faraone et al., 2015; E. G. Willcutt et al., 2005). Several studies reported MPH-related improvements on both cognition and academic performance (Murray et al., 2011; S B Wigal, Gupta, Heverin, & Starr, 2011), but none of these studied the mediating role of cognition on MPH-effects. As previous research implicates these cognitive functions as important for academic performance (Biederman et al., 2004; Mayes & Calhoun, 2007b; Preston et al., 2009; Thorell, 2007), it is plausible that MPH-related improvements in cognition explain part of the relation between MPH and academic performance. Moreover, as children with ADHD show decreased motivation for schoolwork, altered sensitivity to feedback and reward, and lower self-perceived competence (Carlson, Booth, Shin, & Canu, 2002; Groen et al., 2008; Luman, Oosterlaan, & Sergeant, 2005; Luman, Van Meel, Oosterlaan, Sergeant, & Geurts, 2009; Scholtens, Rydell, & Yang- Wallentin, 2013), motivational impairments are likely to further contribute to academic underperformance of children with ADHD. Moreover, MPH-related improvements in motivation are probable because stimulant medication affects dopamine-based brain networks, including the ventral striatum, which is active during reward processing (Volkow et al., 2004). Activity in these networks improves motivation to perform (Shiels et al., 2009; Swanson et al., 2004), which makes it likely that MPH improves aspects of academic motivation in children with ADHD.