The conflict adaptation effect in Parkinson's disease: a study with EEG

Although several investigations focused on cognitive impairments in Parkinson's disease (PD), the results are ambiguous and the mechanisms of these findings remain unclear. In this project we study the cognitive control of conflict adaptation, using scalp-recorded event-related potentials (ERP). We also investigated the flanker interference effect in PD, compared to healthy controls (HCs). 20 PD patients and 20 HCs matched to the PD patients by age and gender were investigated with electroencephalography (EEG) while they performed a modified Eriksen flanker task, requiring a relatively high cognitive control. Our hypothesis was that behavioral and electrophysiological reflections of conflict adaptation would be reduced in PD patients. We examined reaction times (RT), event-related potential correlates of conflict processing (fronto-central N2 component) and response preparation (lateralized readiness potentials, LRP). Consistent with the conflict monitoring theory, HCs showed attenuation of RTs and N2 amplitudes on incongruent trials following incongruent trials compared to incongruent trials following congruent trials, reflecting a reliable conflict adaptation effects in RTs and N2 amplitudes. In the PD group this effect was lacking. LRPs showed that incorrect response activation related to the incongruent flankers had significantly smaller amplitude in PD patients compared to HCs. In HCs, incorrect response activation decreased on incongruent trials following incongruent trials compared to incongruent trials following congruent trials. In PD patients this effect does not reach significance.