There is considerable consensus that impairment in executive functions (EF) constitutes a central source of the disability in children and adolescents with ADHD. Recent studies, however, have reported that EF test results are only weakly related to the severity of ADHD symptoms.
These findings have led to an increased interest in how EF impairments appear in complex everyday situations where motivational processes interact with EF.Knowledge about this interplay between EF and motivation in children and adolescents with ADHD is scarce. In particular, the degree and type of impairment across ADHD subtypes and genders remains unclear. Therefore, the first aim of this study (paper I) was to compare executive processes with pronounced (hot EF) and less pronounced (cold EF) motivational salience in children and adolescents with ADHD-combined (ADHD-C) and ADHD-inattentive (ADHD-I) subtypes relative to typically developing (TD) children. Our findings supported and expanded on previous studies reporting cold executive dysfunction in children and adolescents with ADHD. There were few differences between ADHD subtypes. Hot EF performance was not impaired in any of the ADHD subtypes relative to TD children.
As most EF tests are highly complex and involve many different sub-processes (both EF and non-EF), low test specificity of the EF tests may hamper the identification of distinct EF profiles in ADHD subtypes. The second aim of the study (paper II) was therefore to investigate cognitive inhibition in a forced attention dichotic listening (DL) task in children with ADHD-C, ADHD-I, and TD children. Results demonstrated impaired cognitive inhibition in both ADHD subtypes, but also significantly greater impairment in the ADHD-I group relative to the ADHD-C group. As far as we know, this study is the first to demonstrate distinct levels of inhibitory impairment between ADHD subtypes in children and adolescents using the DL task.
With regard to gender, previous research has yielded more similarities than differences in cold EF profile for girls and boys with ADHD. However, different symptom expression in boys and girls with ADHD seem to cause referral bias leading to under identification and lack of treatment for females with ADHD. In addition, the presence of co-existing symptoms often clouds the diagnostic picture. The third aim in our study (paper III) was to explore whether there were gender differences in co-existing symptom severity and EF impairment in children and adolescents with ADHD. Self-report and parent rating scales were used to assess co-existing symptoms, whereas EF impairment was assessed with cold EF tests and parent-ratings of EF problems in everyday life. Our results indicate that EF problems in everyday life are more pronounced in boys with ADHD compared to girls with ADHD, despite similar levels of impairment on cold EF tests. In contrast, co-existing problems are more prominent in girls with ADHD. In particular, self-report scales seem to increase awareness of internalizing problems in females with ADHD. These findings elucidate the combined value of self-report and parent rating scales for the identification of EF problems and comorbid symptoms in boys and girls diagnosed with ADHD.
The fourth aim of the study (paper IV) was to investigate the development of hot and cold EF in boys and girls with ADHD relative to TD counterparts after two years. We found that cold EF remained impaired compared to TD children, despite improved performance across time in the ADHD group. A decline in co-existing problems and ADHD symptoms showed few associations with improved cold EF performance across time. Females with ADHD outperformed TD counterparts on the hot EF task at baseline, but showed deteriorating hot EF performance across time. In contrast, TD females showed improved hot EF performance across time. Our findings indicate that hot and cold EF show divergent developmental trajectories, which are relatively independent from co-existing problems and ADHD symptomatology in children and adolescents with ADHD.
Possible clinical implications of the studies may be that parent ratings of EF seem more suitable than neurocognitive testing to differential diagnosis of ADHD-C and ADHD-I. Further, it may be important to address the issue of techniques to improve cognitive inhibition for children and adolescents with ADHD. Finally, the combination of self-report and parent rating scales are important for the identification of different comorbid symptom expression in boys and girls diagnosed with ADHD.