Thesis defense Daniel von Rhein (Donders series 203)

21 December 2015

Promotors: prof dr. J. Buitelaar, prof. dr. R. Cools  Copromotor: dr. M. Mennes

Neural mechanisms of reward processing in attention deficit hyperactivity disorder

Attention-deficit/hyperactivity disorder (ADHD) is a common, neurodevelopmental disorder that occurs early in life and is characterized by enduring problems in the ability to focus attention and to regulate impulsivity and motor activity (American Psychiatric Association 2013). Experimental cognitive research in this field has robustly demonstrated that participants with ADHD have deficient executive functions (Willcutt et al. 2005). Relatively recently, deficits were also shown for reward-related processes (Luman et al. 2010). Studies on the neural processes underlying these reward-related deficits were mainly done in adult participants with ADHD consistingly reporting deficient signaling in reward processing brain circuits. For young participants with ADHD, however, only a few studies with small sample size exist and empirical findings are inconsistent. Therefore, the overall aim of this thesis is to examine the behavioral and neural processes involved in the processing of reward in a large population of young participants with ADHD, providing additional clues about the neurobiological basis of ADHD.

This thesis presents the NeuroIMAGE study, a prospective phenotypic, cognitive, genetic and MRI study in young participants with ADHD. Central elements of the thesis are four published research articles that shed light on different aspects of reward processes in ADHD. The first research article answers the question whether we can segregate neural processes during anticipation and receipt of reward that are altered in participants with ADHD and whether such measures are valid endophenotypes (Chapter 3). The second research article describes these reward-related neural processes from a network perspective and investigates, whether participants with ADHD show deficient functional integration of neural networks implicated in reward processing (Chapter 4). The third article shows whether the generic functional architecture of reward-related, attentional and motor control networks contribute to the functional neural changes observed in ADHD (Chapter 5). The final article addresses the question whether there is evidence for reward-related neural processes that are specific to either symptoms of ADHD, or symptoms of autism, or a combination of both disorders (Chapter 6).