Background and Aims The characteristic symptoms of chorea in Huntington's disease, have been related to a dysfunction of dopamine transmission. Furthermore, psychological symptoms like anhedonia and altered motivation and drive as functions of the dopaminergic reward system are common and often manifest already early in the course of the disease. Investigating the reward system using monetary incentive tasks with neuroimaging has been demonstrated as a feasible tool to investigate and characterise mesolimbic dopaminergic functions in healthy subjects and patients with neurpsychiatric diseases.

Methods Using fMRI, we scanned 14 presymptomatic carriers of the Huntington gene aged 26–56 (eight females) and 14 control subjects matched one-to-one regarding age, gender and education. Mean calculated years to onset of the illness in the gene carriers were 19.6 (SD 11.6). We used an established event-related gambling game task with five levels of probability, that is, per cent chance to win €1 (0%, 25%, 50%, 75% and 100%). After a cue announcing reward probability and an expectation period, subjects reacted with a button press to two different stimuli. By pressing the correct button, they preserved themselves the announced chance to win. Rewards were displayed after the button press (outcome).

Results Behaviorally, reaction times in both, patients and control subjects showed a marked acceleration of reaction times towards higher reward probabilities reflecting a good commitment to the task and intact motivational reactivity in both groups. The ANOVA modelling increasing reward expectations revealed a larger network of activated reward-related brain regions in the patients than in the control subjects. The effect was less pronounced for the ANOVA set up to model the prediction error upon receipt or omission of rewards.

Conclusions Our results can be interpreted in the sense of a hypercompensation with the recruitment of larger networks upon reward processing in presymptomatic carriers of the Huntington gene. Similar results have been demonstrated for Alzheimer's disease as another example for a neurodegenerative disease. Larger network recruitment was interpreted as a possible compensation for early neuronal degeneration, helping to keep up behavioural functioning.