Abstract
The key cognitive impairments of children with attention deficit/-hyperactivity disorder (ADHD) include executive control functions such as inhibitory control, task-switching, and working memory (WM). In this training study we examined whether task-switching training leads to improvements in these functions. Twenty children with combined type ADHD and stable methylphenidate medication performed a single-task and a task-switching training in a crossover training design. The children were randomly assigned to one of two groups. One group started with the single-task training and then performed the task-switching training and the other group vice versa. The effectiveness of the task-switching training was measured as performance improvements (relative to the single-task training) on a structurally similar but new switching task and on other executive control tasks measuring inhibitory control and verbal WM as well as on fluid intelligence (reasoning). The children in both groups showed improvements in task-switching, that is, a reduction of switching costs, but not in performing the single-tasks across four training sessions. Moreover, the task-switching training lead to selective enhancements in task-switching performance, that is, the reduction of task-switching costs was found to be larger after task-switching than after single-task training. Similar selective improvements were observed for inhibitory control and verbal WM, but not for reasoning. Results of this study suggest that task-switching training is an effective cognitive intervention that helps to enhance executive control functioning in children with ADHD.
Highlights
The main goal of the present study was to determine the range of plasticity in executive control functioning in children with attention deficit/-hyperactivity disorder (ADHD)
Behavioral deficits observed in children with ADHD are characterized by inattention, impulsivity, and hyperactivity (American Psychiatric Association, 1994), and it has been suggested that those deficits are primarily related to executive control impairments, such as inhibitory control and working memory (WM) (Barkley, 1997; Willcutt et al, 2005)
Children with ADHD showed a reduction of switching costs throughout the task-switching training, suggesting that they already benefited from a relatively short intervention of four training sessions
Summary
The main goal of the present study was to determine the range of plasticity in executive control functioning in children with attention deficit/-hyperactivity disorder (ADHD). One experimental task that has frequently been applied in recent years to examine executive control functioning is the taskswitching paradigm (for a recent review; Kiesel et al, 2010) The advantage of this paradigm is that it allows the separation of different components of executive control, such as task-set selection and maintenance, task-set switching, and interference control (Cepeda et al, 2001). Performance can be measured in mixedtask blocks, in which the participants have to switch between both tasks A and B on every second trial, and in single-task blocks, in which only one of the tasks (A or B) has to be performed (Kray and Lindenberger, 2000; Kray et al, 2008) This allows the determination of two types of performance costs associated with the switching situation: mixing costs are defined as the difference in mean performance between mixed-task and single-task blocks and are assumed to refer to the ability to maintain two task sets and select between them. The efficiency of interference control can be measured by comparing the performance on congruent trials (in which the number and value decisions are not conflicting, i.e., 1, 333) with performance on incongruent trials (in which the number and value decisions are conflicting, i.e., 3, 111), Frontiers in Human Neuroscience www.frontiersin.org
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