Action impulsivity and attention deficits in patients at an early stage of Huntington disease.

Huntington's disease (HD) is characterized by a combination of motor, cognitive, and neuropsychiatric impairments. Among them, impulsivity and attention deficits are clinical features usually described in HD, impacting the quality of life of patients and their caregivers. Twenty early-stage HD patients (PHD) and 20 age and gender-matched control participants (CP) performed a "Simon" reaction time (RT) task allowing us to explore action impulsivity and attention deficits. Surface EMG recordings aimed at revealing the presence and characterizing the nature of impulsivity in PHD. Correlational analyses between error rates or chronometric data, and clinical or neuropsychological data were examined. (1) Analysis of the accuracy and EMG patterns revealed no difference between PHD and CP, indicating absence of motor impulsivity at the early stage of HD. (2) Chronometric indices revealed a general slowing of information processing in PHD, involving central information processing but sparing the latest stages of motor execution, consistent with performed correlational analysis. (3) Sequential analysis of RT patterns showed a failure to allocate attention appropriately. These indices of attentional deficits nicely correlated with performance in neuropsychological tests exploring attentional processes. (1) Central information processing slows down at the early stage of HD but the latest steps of motor execution are unaffected. (2) In the progression of HD, attentional deficits typically should appear first among dysexecutive problems, without significant action impulsivity.