Differential reward processing in subtypes of adult attention deficit hyperactivity disorder

Objectives: Abnormalities in reward processing have been found in adolescents and adults with ADHD using the 'Monetary Incentive Delay' (MID) task. However, ADHD groups in previous studies were heterogeneous regarding ADHD subtype, gender and, in part, drug treatment status. This study sought to compare neural activations in the ventral striatum (VS) and prefrontal regions during reward processing in homogenous ADHD subtype groups and healthy adults, using the MID task. Methods: In total, 24 drug-naive, right-handed male adults with ADHD (12 subjects with combined type (ADHD-ct) and 12 subjects with predominantly inattentive (ADHD-it) type ADHD), and twelve healthy right-handed male control subjects were included. Results: Compared to ADHD-ct and healthy subjects, ADHD-it subjects showed a bilateral ventral striatal deficit during reward anticipation. In contrast, ADHD-ct subjects showed orbitofrontal hyporesponsiveness to reward feedback when compared with ADHD-it and healthy subjects. Conclusions: This is the first fMRI study that delineates dysfunctional and subtype-divergent neural and behavioural reward processing in adults with ADHD. (C) 2012 Elsevier Ltd. All rights reserved.