! "# $ % &'% () *' ("*+ '' +,"' -'*"+ --'*' . Dissertation for the Degree of Doctor of Philosophy in Psychology presented at Uppsala University in 2003 ABSTRACT Berlin, L. 2003. The Role of Inhibitory Control and Executive Functioning in Hyperactivity/ADHD. Acta Universitatis Upsaliensis. Comprehensive Summaries of Uppsala Dissertations from the Faculty of Social Sciences 120. 76 pp. Uppsala. ISBN 91-544-5513-1. This thesis examined inhibition, executive functioning and their possible relation to childhood problems of hyperactivity and inattention, in its clinical form referred to as Attention Deficit Hyper- activity Disorder (ADHD). Concurrent as well as longitudinal relations were of interest, and both clinical and non-clinical samples were studied. Study I demonstrated concurrent relations between executive inhibition and both hyperactivity and conduct problems in preschool. However, the relation between inhibition and conduct problems could be attributed to the large overlap between hyperactivity and conduct problems. In Study II, linear relations were found between executive inhibition and hyperactivity, whereas inhibition to the unfamiliar was related to hyperactivity, social initiative, as well as social anxiety. Non-linear analyses showed that children with high levels of both types of inhibition were at risk for developing low social initiative and social anxiety, whereas children with low levels of inhibition were at risk for developing hyperactivity, but at the same time protected from social anxiety. In Study III, executive inhibition was longitudinally related to ADHD symptoms in both school and at home for boys, but only in the school context for girls. Executive inhibition was also related to more general executive functioning deficits, and concurrent relations were found between executive functioning and ADHD symptoms, although in both cases only for boys. Inhibition and executive functioning made independent contributions to the understanding of ADHD symptoms for boys, and together explained about half the variance in inattention problems. In Study IV, group differences were found between ADHD children and controls for both inhibi- tion and various other executive function measures. These measures also discriminated well between groups. The best model, which included measures tapping inhibition, working memory and emotion regulation, classified 86% of the children correctly. In summary, the results of the present thesis were mostly supportive of Barkley’s hybrid model of ADHD, although it should be noted that the question of whether inhibition should be regarded as pri- mary to other executive functions requires further investigation. Key words: ADHD, hyperactivity, inhibition, executive functioning, development Lisa Berlin, Department of Psychology, Uppsala University, Box 1225, SE-751 42 Uppsala, Sweden Lisa Berlin, 2003 ISSN 0282-7492 ISBN 91-554-5513-1 Printed in Sweden by Kopieringshuset, Uppsala, 2003 2 The present thesis is based on the following studies, which will be referred to in the text by their Roman numerals: I Berlin, L. & Bohlin, G. (2002). Response inhibition, hyperactivity, and conduct problems among preschool children. Journal of Clinical Child and Adolescent Psychology, 31, 242-251. II Berlin, L., Bohlin, G., & Rydell, A-M. (2002). Two types of inhibitory control: predictive relations to social functioning. Manuscript under revision for publica- tion. III Berlin, L., Bohlin, G. & Rydell, A-M. (2002). Relations between inhibition, executive functioning, and ADHD-symptoms: A longitudinal study from age 5 to 8½ years. Manuscript under revision for publication. IV Berlin, L., Bohlin, G., Nyberg, L., & Janols, L-O. (2002). How well do measures of inhibition and executive inhibition discriminate between ADHD children and controls? Manuscript submitted for publication. Reprints were made with kind permission from the publishers. 3 ABBREVIATIONS ADHD Attention Deficit Hyperactivity Disorder ADHD-C ADHD, combined subtype ADHD-HI ADHD, predominantly hyperactive/impulsive subtype ADHD-I ADHD, predominantly inattentive subtype ANOVA Analysis of variance COWAT Controlled Word Association Test MANOVA Multiple analysis of variance APA American Psychiatric Association BAS Behavioral Activation System BIS Behavioral Inhibition System CBQ Child Behavior Questionnaire CD Conduct Disorder CPT Continuous Performance Test DSM-IV Diagnostical and Statistical Manual of Mental Disorders, 4th edition EI Executive inhibition ES Effect size IU Inhibition to the unfamiliar NAS Nonspecific Arousal System ODD Oppositional Defiant Disorder PBQ Preschool Behavioral Questionnaire SCI Social Competence Inventory WISC-III Wechsler Intelligence Scale for Children, 3rd edition 4 TABLE OF CONTENTS ABBREVIATIONS................................................................................................................. 4 TABLE OF CONTENTS........................................................................................................ 5 INTRODUCTION................................................................................................................... 9 Defining Hyperactivity/ADHD............................................................................................10 Diagnostic criteria........................................................................................................10 Subtypes of ADHD......................................................................................................10 The etiology of ADHD ................................................................................................12 Defining Inhibitory Control..................................................................................................13 Executive inhibition (response inhibition) ................................................................13 Inhibition to the unfamiliar .........................................................................................14 Defining Executive Functioning ..........................................................................................15 Theories of ADHD ................................................................................................................16 Barkley's hybrid model of ADHD..............................................................................16 Non-verbal working memory............................................................................16 Internalization of speech (verbal working memory) ......................................18 Self-regulation of affect/motivation/arousal....................................................18 Reconstitution......................................................................................................18 The Gray/Quay theory of BIS and BAS....................................................................19 Rothbart's theory of effortful control.........................................................................20 The cognitive energetic model....................................................................................20 An overview of previous research.......................................................................................21 Executive functioning and hyperactivity/ADHD.....................................................21 Inhibition to the unfamiliar and hyperactivity/ADHD ............................................22 Critical issues in hyperactivity/ADHD research................................................................23 Comorbidity..................................................................................................................23 Conduct disorder and oppositional defiant disorder.......................................23 Social anxiety......................................................................................................23 Should ADHD be regarded as a category or as a dimension?................................24 The possibility of preschool prediction.....................................................................25 Sex differences..............................................................................................................26 Relations between ADHD, executive functioning, and intelligence .....................26 The discriminant ability of tests of executive functioning ......................................27 Aims of the thesis ..................................................................................................................28 EMPIRICAL STUDIES........................................................................................................30 METHOD ..............................................................................................................................30 Participants and procedures..................................................................................................30 Longitudinal study (Study I, II and III) .....................................................................30 5 Clinical study (Study IV) ............................................................................................31 Measures….............................................................................................................................32 Executive inhibition.....................................................................................................32 Go/no-go tasks.....................................................................................................32 Stroop-like