Children with Attention Deficit Hyperactivity Disorder (ADHD): Reinforcement sensitivity theory, executive functioning impairment and avoiding mental effort

Attention Deficit Hyperactivity Disorder (ADHD) is a neurodevelopmental disorder that includes avoiding mental effort and executive functioning impairment. Reports demonstrate that abnormalities in inhibition, working memory, and reinforcement sensitivity play a role. However, the interplay of these factors in the observed executive impairment and frequently avoiding mental effort is not well understood. In this thesis, three investigations were undertaken to expand our understanding of the interplay of these specific impairments and, thus, underlying nature of ADHD. In the first study, the Reinforcement Sensitivity Theory-Personality Questionnaire-Children (RST-PQ-C) version was translated in order to assess reinforcement sensitivity among Turkish speaking children. In total, 738 primary school students age ranging from 7 to 11 completed the RST-PQ-C as well as the Academic Motivation Scale. Data were analysed using confirmatory factor analysis, hierarchical multiple regression, and structural equation modelling techniques. The results confirmed the hypothesized three-factor structure and the expected relationships between the obtained factors and academic motivation. Evidence is provided to demonstrate that the translated RST-PQ-C is a reliable tool to assess reinforcement sensitivity among Turkish speaking children. Study 2 was divided into two parts (Study 2a and Study 2b) reflecting the two problems under investigation. The whole study included one clinical group (40 children with ADHD, aged between 7-11 years) and one control group (40 children without ADHD, aged between 7-11 years). The same data set was used in both investigations of Study 2. Study 2a aimed to investigate the role of inhibition in effort avoidance. A method that employs nine neuropsychological tests for quantifying avoidance behaviour (dependent variable) was developed. Data from the Go/no-go Task (independent variable) and the RST-PQ-C (the behavioural inhibition system, BIS, as the mediator) was analysed in a simultaneous predictive model using moderated mediation analysis. Results demonstrated that prepotent response inhibition had a significant indirect effect on the frequency of avoidance through the BIS and this effect was contingent on the ADHD diagnosis. Based on these findings it can be concluded that the weak prepotent motor response inhibition and the hypoactive BIS result in a higher rate of avoiding mental effort among children with ADHD. Study 2b aimed to investigate the effect of working memory (WM) load and the fight, flight, freeze system (FFFS) of the revised reinforcement sensitivity theory on executive functioning. Data from the Go/no-go Task, the Working memory-switch Task and the RST-PQ-C were analysed. Mixed repeated measures ANOVA and ANCOVA results showed that the higher WM load and higher FFFS activity resulted in the impaired executive functioning performance among children with ADHD. Based on these findings it can be concluded that maintaining WM load consumes controlled attention resources and leads to a resource allocation problem that hinders the optimal executive functioning performance among children with ADHD. The theoretical implications and practical clinical implications of these results are discussed. Key words: ADHD, Reinforcement sensitivity theory, inhibition, working memory, avoiding mental effort, impaired executive functionin