Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article


Master of Arts




Duerden, Emma G.


Problem behaviours associated with Attention Deficit Hyperactivity Disorder (ADHD) symptomatology put children at increased risk of experiencing peer victimization, which has been associated with altered brain development and cognitive ability. A large sample of typically developing (TD), ADHD combined type (ADHD-C), and ADHD inattentive type (ADHD-I) children underwent behavioural assessment, magnetic resonance imaging (MRI) and cognitive testing. We examined how problem behaviours and peer victimization differed among the groups, how problem behaviours and peer victimization related to hippocampal volume, and how hippocampal volume related to working memory (WM). The ADHD-C group displayed the highest levels of peer victimization and problem behaviours. We found that left Cornu Ammonis 3 (CA3) volume was a positive predictor of peer victimization and of WM ability, while left Cornu Ammonis 4 (CA4) negatively predicted WM. Interventions targeting peer victimization in schools may help reduce adverse brain and cognitive outcomes, particularly in children with ADHD-C.

Summary for Lay Audience

Attention Deficit Hyperactivity disorder (ADHD) consists of three different subtypes including ADHD Inattentive type (ADHD-I) characterized by elevated symptoms of inattention, ADHD Hyperactive-Impulsive type (ADHD-H), characterized by elevated symptoms of hyperactivity-impulsivity, and ADHD Combined type (ADHD-C), characterized by elevated symptoms in both domains. Many children and adolescents with ADHD have social difficulties, however children with more severe hyperactive-impulsive symptoms display more problem behaviours, like talking out of turn and not following rules, that increase their risk of experiencing bullying by their peers. Peer victimization can cause severe stress, and even alter the development of a brain region, known as the hippocampus, which is involved in learning and memory. In turn children with ADHD may be at risk for social problems, stress, and alterations in brain development and working memory (WM). This thesis addressed three main aims. First, we examined how levels of problem behaviours and peer victimization differ between typically developing (TD) children and those with two different ADHD subtypes, including ADHD-I and ADHD-C. Our second aim was to examine whether hippocampal size was related to levels of problem behaviours and peer victimization. Our third aim was to examine if hippocampal volume could predict WM abilities. We found that the ADHD-C group displayed the most severe levels of problem behaviour and experienced the most peer victimization. We also found that regional alterations in the development of the hippocampus was associated with peer victimization and WM. This suggests that school-based interventions aimed at reducing peer victimization in schools may be key to promoting brain and cognitive health.