Selective executive dysfunction but intact risky decision-making in early Huntington's disease

Executive dysfunction, including problems with decision-making, inhibition of prepotent responses, and verbal fluency, are main features of Huntington's disease (HD). The decline of executive function in HD is related to the anatomical progression of HD pathology in the basal ganglia, where the earliest changes of neuronal cell death are seen in the dorsolateral caudate. To examine the specific pattern of executive dysfunction in early HD, 18 patients with early HD were assessed on: (1) the Iowa Gambling Task to measure risky decision making, (2) the Stroop test to measure inhibition of prepotent responses, and (3) the verbal fluency test to measure internally guided word search and production, necessitating suppression of retrieval/production of inappropriate words and monitoring of the output. Patients with early HD were significantly impaired on the Stroop and verbal fluency tests relative to controls. However, Iowa Gambling Task performance was comparable across the 2 groups. This pattern of selective executive dysfunction in early HD probably reflects the fact that inhibitory processing involved in both the Stroop and verbal fluency tests recruits the dorsolateral caudate and its cortical connections, which are dysfunctional in early HD, whereas risky decision-making during the Iowa Gambling Task recruits the ventromedial caudate and its connections, which remain spared early on in the disease. The current results demonstrate that the deterioration of executive functioning in HD is variable and that some types of executive processing might already be impaired in early HD, whereas others remain intact.