Lilianne Nyberg

How well do measures of inhibition and other executive functions discriminate between children with ADHD and controls

The aim of the present study was to evaluate the usefulness of Barkley’s (1997a) model of inhibition and executive functioning in describing the deficits associated with Attention Deficit Hyperactivity Disorder (ADHD). Besides group differences, the present study addressed the question of independent effects of inhibition and the other executive functions in discriminating between children with ADHD and controls and how well, in terms of sensitivity and specificity, these measures can classify the children into the correct group. The results showed that children with ADHD differed significantly from controls with regard to measures of inhibition as well as all other executive function measures, except repetition of hand movements. In logistic regression models, three different measures tapping inhibition, working memory and emotion regulation were shown to be significant independent predictors of group membership. The sensitivity for these three variables as a set was 76.2, the specificity was 90.5, with a total of 86% of the sample correctly classified. When excluding the parental rating of emotion regulation, the overall classification rate decreased some, but was still relatively high in comparison with previous studies within this area of research.

The Childhood Executive Functioning Inventory (CHEXI): A New Rating Instrument for Parents and Teachers

Poor executive functioning has been shown to be of central importance in disruptive behavior disorders such as attention deficit hyperactivity disorder (ADHD), and a large number of laboratory measures of executive functioning have been developed. There are, however, few available questionnaires tapping executive functioning and those that exist also include items focused directly on the symptom criteria for ADHD, which makes it difficult to draw conclusions regarding executive functioning per se. In the present study, a new rating instrument, the Childhood Executive Functioning Inventory (CHEXI) was therefore introduced. This instrument was shown to have good test-retest reliability. Using factor analysis, two factors tapping working memory and inhibition emerged using parent ratings and these two factors were replicated using teacher ratings. Modest, yet mostly significant, relations to laboratory measures of working memory and inhibition were found. Ratings on the CHEXI were also found to be significantly related to ADHD symptoms as well as early academic achievement. Interestingly, ratings on the CHEXI and laboratory measures of working memory and inhibition were shown to explain independent variance in ADHD symptoms and academic achievement, which point to the importance of using a multi-assessment strategy when studying executive functioning.

The proposed interaction between working memory and inhibition

Two experiments investigated the determinants of performance on a go/no-go task by studying the interplay of two executive function components, working memory (WM) and inhibition. Systematically varied task demands on WM and inhibition were used in the analysis of performance together with individual capacity measures of both functions, thereby investigating an interactive view of WM and inhibition. Further analyses were conducted with individual differences in general fluid intelligence (gF), in an attempt to study the role of higher order cognition in handling task demands. The results are new in presenting empirical evidence for interactive effects of the task demand variables in concert with individual WM capacity as well as with gF, suggesting that executive processes common to WM and gF are involved in inhibitory performance, whereas gF appears to reflect a broader function in controlling behaviour in relation to task goals, whether it involves active responding or not.

Inhibition and executive functioning in Type A and ADHD boys.

The present study was aimed at clarifying the standing of Type A behavior, as measured by behavioral observations, relative to Attention Deficit Hyperactivity Disorder (ADHD), using measures of inhibitory control and executive functioning. The study sample included 20 boys exhibiting Type A behavior, 21 boys exhibiting Type B behavior and 14 boys diagnosed with ADHD, ranging in age from 7 to 12 years. The results of the present study showed that the Type A children differed from Type B children on two time-related variables, response latency and reaction time, in accordance with the view of Type As as time-urgent and impatient. Furthermore, in comparisons with the ADHD group, the Type A boys were found to be superior on several performance tasks, such as Go/no-go omissions, time reproduction, story recall and memory for sequences of hand movements, although similarities between Type A and ADHD boys were evidenced in terms of response latency and reaction time. In other words, although Type A boys were similar to ADHD boys in terms of overt displays of time-urgency and impatience, Type As do not display deficits with regard to executive functioning, of the kind often found when ADHD children are compared with normal controls. It may thereby be concluded that Type A behavior and hyperactivity/ADHD appear to be well differentiated except with regard to what may be interpreted as impatience. Speculations concerning differing origins of overtly similar characteristics of Type A behavior and ADHD should be considered in future research.