Reward processing in male adults with childhood ADHD--a comparison between drug-naïve and methylphenidate-treated subjects.

Rationale: Dysfunctional reward processing has been proposed as a main deficit in attention-deficit/hyperactivity disorder (ADHD), which could be modulated by treatment with methylphenidate (MPH).

Objectives: We examined differences in reward processing in adulthood (independent of actual ADHD) depending on MPH treatment during childhood.

Methods: Eleven males with childhood ADHD treated with MPH, 12 drug-naïve males with childhood ADHD, and 12 controls matched by age, handedness, and smoking behavior were studied drug-free using functional magnetic resonance imaging. BOLD-responses were compared during a monetary incentive delay task using an ANOVA design focusing on the ventral striatum during anticipation and the orbitofrontal cortex during outcome.

Results: Controls, drug-naïve, and treated subjects did not differ significantly in their activations in the ventral striatum and orbitofrontal cortex. Explorative analyses revealed decreased insula activation during outcome of loss avoidance in drug-naïve subjects in comparison to both groups, while treated subjects did not differ from controls. Insula activation correlated significantly positive with harm avoidance in the treated group. Furthermore, comparing subjects with actual ADHD symptoms, remitters and controls we observed decreased putamen activition in ADHD persisters.

Conclusions: Basal ganglia reward processing seemed to be unrelated to MPH pretreatment, but was related to remission. On the other hand, the revealed differences between treated and drug-naïve subjects with childhood ADHD, i.e., in the insula, give evidence for more pronounced abnormal activation in reward-associated brain regions in untreated subjects with childhood ADHD and underpin the need of prospective studies on long-term effects of psychostimulant treatment.