ALTERED REINFORCEMENT MECHANISMS IN ATTENTION-DEFICIT HYPERACTIVITY DISORDER/

The present study tested eight boys with attention-deficit/hyperactivi ty disorder (ADHD) and 12 normal boys (comparison group), aged 7-12 ye ars, to investigate the hypothesis that ADHD is associated with a stee per and shorter delay-of-reinforcement gradient than is normal. A two- component schedule of reinforcement was used to deliver trinkets or co ins as reinforcers in a game-like test. One component was marked by a signal. During this period reinforcers (coins or trinkets) were delive red every 30 s. This component is called a 30-s fixed interval (FI) sc hedule of reinforcement and measures changes in reactivity to reinforc ers. The other component was in effect when the signal was turned off. Then no reinforcer was ever delivered. This is called an extinction ( EXT) component and measures primarily sustained attention. The ADHD ch ildren gradually developed hyperactivity to a large extent consisting of bursts of responses with short interresponse times (IRTs) during bo th schedule components. The response bursts not only constituted a sub stantial portion of the ADHD overactivity, but may well be a key compo nent of the behaviour commonly described as impulsiveness, the key beh avioural characteristic of ADHD. In addition, the ADHD children showed behaviour during the extinction component that may well be described as a sustained-attention deficit: initially stopping when the signal w as turned off and then resuming responding some time thereafter as if the signal had been turned on again. The comparison group ceased respo nding during extinction and did not show impulsiveness. The findings w ere in accordance with a steeper and shorter delay gradient in ADHD. ( C) 1998 Elsevier Science B.V. All rights reserved.