Delay discounting of reward in ADHD: application in young children

Abstract

Background: A key underlying process that may contribute to attention-deficit/hyperactivity disorder (ADHD) involves alterations in reward evaluation, including assessing the relative value of immediate over delayed rewards. This study examines whether children with ADHD discount the value of delayed rewards to a greater degree than typically developing children using a delay discounting task.

Methods: Children aged 7-9 years diagnosed with ADHD and controls completed a task in which they chose between a hypothetical $10 available after a delay (7, 30, 90 and 180 days) versus various amounts available immediately.

Results: ADHD participants discounted more steeply than controls. However, this effect did not survive covarying of IQ.

Conclusions: ADHD is associated with a steeper delay gradient when contemplating hypothetical later rewards, but not independently of IQ. The interplay of cognitive processing and IQ with reward evaluation in ADHD requires further exploration.

Figure 1

Median indifference points for the ADHD and control children on the delay discounting task. Lines represent the hyperbolic functions fitted to these data points for each group with the fitted k and R² values reported. *p ≤ 0.05 using a Mann-Whitney U test to test for differences in indifference points between groups at each delay.

Figure 2

WISC-IVFull Scale IQ as a function of ln(k). Lines represent the linear regression fitted to these data points for each group.

Figure 3

Mean response times as a function of delay for questions that were “hard” (subjective value of both alternatives was almost equivalent by virtue of being close to the indifference point) or “easy” (subjective value of each alternative was different). *p < .05 using a paired samples t-test to compare response times for different question types at the same delay.