Improving working memory in children with attention-deficit/hyperactivity disorder: the separate and combined effects of incentives and stimulant medication

Abstract

Working memory (WM) is considered a core deficit in Attention-Deficit/ Hyperactivity Disorder (ADHD), with numerous studies demonstrating impaired WM among children with ADHD. We tested the degree to which WM in children with ADHD was improved by performance-based incentives, an analog of behavioral intervention. In two studies, WM performance was assessed using a visuo-spatial n-back task. Study 1 compared children (ages 9-12 years) with ADHD-Combined type (n = 24) to a group of typically developing (TD) children (n = 32). Study 1 replicated WM deficits among children with ADHD. Incentives improved WM, particularly among children with ADHD. The provision of incentives reduced the ADHD-control group difference by approximately half but did not normalize WM. Study 2 examined the separate and combined effects of incentives and stimulant medication among 17 children with ADHD-Combined type. Both incentives and a moderate dose of long-acting methylphenidate (MPH; ~0.3 mg/kg t.i.d. equivalent) robustly improved WM relative to the no-incentive, placebo condition. The combination of incentives and medication improved WM significantly more than either incentives or MPH alone. These studies indicate that contingencies markedly improve WM among children with ADHD-Combined type, with effect sizes comparable to a moderate dose of stimulant medication. More broadly, this work calls attention to the role of motivation in studying cognitive deficits in ADHD and in testing multifactorial models of ADHD.

Figure 1

Schematic of trial sequence in the 0-back condition for the no-incentive (Panel a) and incentive (Panel b) visits.

Figure 2

Mean n-back accuracy for all Group × Load conditions during the baseline visit (Panel a) and all Group × Incentive × Load conditions during the incentive visit (Panel b) of Study 1. Bars are standard error.

Figure 3

Mean n-back accuracy for all Medication × Incentive × Load conditions in Study 2 (Panel a). Bars are standard error. In Panel b, data are averaged across load to facilitate comparisons among the Medication × Incentive conditions. INC = incentive, MPH = methylphenidate, Plac = placebo.