Conflict and freezing of gait in Parkinson's disease: support for a response control deficit.

We investigated response activation and suppression processes in Parkinson's disease patients with freezing of gait (FOG). Fourteen freezers, 14 nonfreezers, and 14 matched healthy controls performed the attention network task (ANT) and the Stroop task. The former task has more stimulus-response overlap and is expected to elicit stronger irrelevant response activation, requiring more inhibition. Congruency effects were used as a general measure of conflict resolution. Supplementary reaction time (RT) distribution analyses were utilized to calculate conditional accuracy functions (CAFs) and delta plots to measure response activation and suppression processes. In agreement with previous research, freezers showed a general conflict resolution deficit compared with nonfreezers and healthy controls. Moreover, CAFs pointed to a strong initial incorrect response activation in FOG. As expected, conflict resolution impairment was only apparent in the ANT, and not in the Stroop task. These results suggest an imbalance between automatic and controlled processes in FOG, leading to a breakdown in both motor and cognitive response control.