Abstract
BACKGROUND: Huntington's disease (HD) is a heritable degenerative brain disease caused by a mutation in the huntingtin gene with excessive repeats of the base triplet cytosine-adenine-guanine (CAG), which codes for the aminoacid glutamine. HD is associated with a broad spectrum of neurocognitive dysfunction, including deficits in social cognition. The appreciation of fairness rules and reciprocity has not been studied in HD. Based on theoretical considerations suggesting that brain regions known to be affected from HD are involved in economic decision-making, the present study sought to examine HD patients' performance in two neuroeconomic games. METHODS: Twenty-nine manifest HD mutation carriers (20 males, nine females) performed an Ultimatum Game (UG) and a Dictator Game (DG) where third-party punishment of observed unfairness was required. In addition, patients were tested for neurocognition and the ability to understand other people's mental states ("theory of mind"). For comparison, a clinical control group of 30 patients with chronic schizophrenia, and 30 unaffected healthy controls matched for age and verbal intelligence took part in the study. RESULTS: Patients with HD had some appreciation of fairness rules, as they tended to reject unfair offers in the UG similar to controls. However, unlike the other two groups, individuals with HD did not punish observed unfairness from a third-party perspective. This lack of "altruistic punishment" was associated with deficits in executive functioning including working memory, inhibitory control and cognitive flexibility, and to a lesser degree with poor "theory of mind." CONCLUSIONS: HD seems to be associated with impairments in understanding of more complex rules of social exchange. Aside from deficits in executive functioning, this behavior could, in part, be linked to an inability to experience third-party punishment as rewarding.