Multiple deficits in ADHD: executive dysfunction, delay aversion, reaction time variability, and emotional deficits.

BACKGROUND: The notion that ADHD constitutes a heterogeneous disorder is well accepted. However, this study contributes with new important knowledge by examining independent effects of a large range of neuropsychological deficits. In addition, the study investigated whether deficits in emotional functioning constitute a dissociable component of ADHD. METHOD: The study included children with ADHD (n = 102; 7-13 years) and a control sample individually matched with regard to age and gender. The administered tasks were designed to tap into three different neuropsychological domains: executive functions (i.e., working memory, inhibition, and shifting), delay aversion, and reaction time variability. Parent ratings of emotion regulation and a test of emotion recognition were also included. RESULTS: Children with ADHD differed significantly from controls on all measures, except for delay aversion and recognition of disgust. No main effects of gender or interaction effects of gender and group were found. More importantly, executive functioning, reaction time variability, and emotional functioning all contributed independently to distinguishing between children with ADHD and controls. CONCLUSIONS: The current study supports the view of ADHD as a heterogeneous disorder related to multiple neuropsychological deficits. In addition, emotional functioning appears to be an area of importance for ADHD that needs to be incorporated into future theoretical models.

Training and transfer effects of executive functions in preschool children.

Executive functions, including working memory and inhibition, are of central importance to much of human behavior. Interventions intended to improve executive functions might therefore serve an important purpose. Previous studies show that working memory can be improved by training, but it is unknown if this also holds for inhibition, and whether it is possible to train executive functions in preschoolers. In the present study, preschool children received computerized training of either visuo-spatial working memory or inhibition for 5 weeks. An active control group played commercially available computer games, and a passive control group took part in only pre- and posttesting. Children trained on working memory improved significantly on trained tasks; they showed training effects on non-trained tests of spatial and verbal working memory, as well as transfer effects to attention. Children trained on inhibition showed a significant improvement over time on two out of three trained task paradigms, but no significant improvements relative to the control groups on tasks measuring working memory or attention. In neither of the two interventions were there effects on non-trained inhibitory tasks. The results suggest that working memory training can have significant effects also among preschool children. The finding that inhibition could not be improved by either one of the two training programs might be due to the particular training program used in the present study or possibly indicate that executive functions differ in how easily they can be improved by training, which in turn might relate to differences in their underlying psychological and neural processes.

Brief report: manipulation of task difficulty in inhibitory control tasks.

The present study investigated how task difficulty can be manipulated in inhibitory control tasks. Tasks from three widely used task paradigms - a Go/No-Go task, a Stop-Signal task,and a Flanker task - were manipulated on two parameters each (Go/No-Go task: interstimulus interval, prepotency. Stop-signal task: stop-signal-delay, prepotency. Flanker task:number of distractors, size of target stimulus). Participants were 86 children (age 4-6) from a population-based sample. The results showed no significant effects on the Go/No-Go task but both main and interaction effects on the Stop-Signal task and the Flanker task. Together, these findings indicate that task difficulty can be successfully manipulated in inhibitory control tasks. However, the interactive rather than additive effects on performance suggest that the level of one parameter only has the desired effect under certain conditions. This new information about how to manipulate task difficulty is important when adapting tasks for use with children of different ages, as well as when designing training programs for improving inhibitory control among children with ADHD.