Executive function in young preschool children with symptoms of ADHD

The overarching goal of research presented in this thesis was to provide new knowledge about basic, self-regulatory skills- or executive function (EF)- in young preschool children with behavioral symptoms characteristic of Attention-Deficit/Hyperactivity Disorder (ADHD). Etiological models of ADHD emphasize an onset during kindergarten and preschool years, and neuropsychological theories have converged on deficits in early developing EF processes as a possible developmental pathway towards ADHD. Despite a growing interest in EF development and the introduction of several developmentally appropriate methods of EF measurement for use with the youngest age groups, studies addressing EF in young children with elevated levels of ADHD symptoms are still scarce. Research hypotheses in this thesis had thus to be based on theoretical models of EF development, together with findings from the preschool group as a whole (pooled data from children aged 3 –6 years), and from older children. We hypothesized that EF structure in early preschool years would differ from that described in older children (Paper II), but that associations between deficiencies in early emerging EF processes and symptoms of ADHD would be identifiable. This was expected to hold both when EF was assessed through neuropsychological tests (Paper I), and by use of parents’ ratings of EF behavior in everyday settings (Paper III). The relationship between clinically administered tests of EF and parents’ ratings of EF behavior was specifically addressed in an additional empirical chapter. Our results indicate that at age three, some differentiation has taken place, which is measurable both by neuropsychological tasks and ratings of EF behavior in everyday settings. Labels used to define EF subcomponents in school-aged children and adolescents may not map directly onto emerging EF skills during early preschool years. Performance on neuropsychological tests of inhibition and working memory were related to symptoms of ADHD in our sample. Effect sizes were small, limiting the measures’ clinical utility at this early stage in development. Behavioral ratings of EF in these two domains were more closely related to symptoms of ADHD than the performance-based measures. According to parent ratings of EF, children meeting diagnostic criteria for ADHD presented with higher problem scores across EF domains, and a different EF profile relative to children with internalizing problems and typically developing controls. We found that performance-based measures of EF and ratings of EF behavior were related in our sample. These two methods of measurement are likely to tap into different aspects of early EF and should not be used interchangeably as parallel measures of EF