The basal ganglia are assumed to be of importance in action/response selection, but results regarding the importance are contradictive. We investigate these processes in relation to attentional processing using event-related potentials (ERPs) in Huntington's disease (HD), an autosomal genetic disorder expressed by degeneration of the basal ganglia, using a flanker task. A symptomatic HD group, a presymptomatic HD group (pHD), and healthy controls were examined. In the behavioral data, we found a general response slowing in HD while the compatibility effect was the same for all groups. The ERP data show a decrease of the N1 on the flanker in HD and pHD; this suggests deficient attentional processes. The N1 on the target was unaffected, suggesting that the attentional system in HD is not entirely deficient. The early lateralized readiness potential (LRP), reflecting automatic response activation due to the flankers, was unchanged, whereas the late LRP, reflecting controlled response selection due to the target information, was delayed in HD. Thus levels of action-selection processes are differentially affected in HD with automatic processes seeming to be more robust against neurodegeneration. The N2, usually associated with conflict processing, was reduced in the HD but not in the pHD and the control groups. Because the N2 was related to the LRP and reaction times in all groups, the N2 may generally not be related to conflict but rather to controlled response selection, which is impaired in HD. Overall, the results suggest alterations in attentional control, conflict processing, and controlled response selection in HD but not in automatic response selection.
Ideomotor compatibility enables automatic response selection