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(2009) Delay and reward choice in ADHD: an experimental test of the role of delay aversion., Neuropsychology, 23, 367-380. [Request a copy] View Article

Introduction: ADHD is clinically and etiologically heterogeneous. The potential value of identifying neuropsychological sub-types within the broader ADHD phenotype has recently been proposed. This study examines the credentials of delay aversion as a marker of a motivational subtype by examining performance on a simple task offering a choice between smaller-sooner and larger-later rewards in a large sample of clinically ascertained cases.

Methods: 376 ADHD probands; 374 siblings and 219 non-ADHD controls (Cs) on the Maudsley Index of Delay Aversion (MIDA) made choices between smaller sooner (SS: 1 point after 2 sec) & larger later (LL: 2 points after 30 sec) outcomes. There were two conditions; post reward delay (PRD: trial length was equalised by the addition of a delay after a reward) and no-post reward delay (NPRD: trial length determined by pre-reward delay levels).

Results:
1 - ADHD children chose SS more than Cs under both conditions -- & this effect was larger under the no-post delay than the post-delay condition.

2 - These effects were much stronger in children under 12 y-old.

3 - About 30 % of this group of children with ADHD met criteria for delay aversion (chose SS more than 50 percent of trials) vs. 12% in siblings and 8% in Cs.

4 - Delay averse & non-delay averse children could be distinguished from one another in terms of (i) lower IQ by 5 points, (ii) younger age by 2.5y, (iii) increased risk of comorbid conduct disorders; (iv) siblings who themselves were at increased risk of delay aversion.

4 - Delay-averse children were not distinguishable on gender, symptom severiy (impulsivity, overactivity or inattentive symptoms).

Discussion: These data provide the strongest support to date for a) delay aversion as an important association of ADHD in younger children by confirming the dual component basis of ADHD children's preference for SS over LL. b) Like other neuropsychological characteristics -- delay aversion affects only a minority of ADHD cases, but this sub-group differs from other children in clinically important ways. c) Evidence of familial co-segregation provides the first evidence that ADHD with delay aversion may represent an etiological subtype of ADHD.

Future research should focus on the genetic architecture of the neuropsychological endophenotype characterized by the conjunction of these clinical characteristics.

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