Involuntary attention impairment in early Parkinson's disease: an event-related potential study

Dopaminergic nigro-striatal depletion interferes with the detection of novel stimuli. This suggests that Parkinson's disease (PD) may generate from the initial stages a failure in involuntary attention (IA), which can be studied through the distraction potential, composed by the mismatch negativity (MMN), the P3a and the reorientation negativity (RON). This study analyzed IA using event-related potentials (ERPs) in patients with early PD with and without dopaminergic replacement therapy. Twenty-five medicated, and 17 non-medicated patients with early PD were studied, as well as 20 healthy control subjects. All subjects performed an auditory distraction task while a digital EEG was being recorded. The distraction potential was obtained by averaging methodology. Each wave was analyzed with a Repeated Measures ANOVA test. The MMN was obtained in all subjects and no significant differences in mean amplitude were found among the groups. There was a main effect of group for the amplitude of P3a (F(2,59)=4.8, p=0.01, ɛ=0.411), with a significant lower amplitude in the medicated group compared to the control group (MD=-1.03, p=0.003). RON also showed a main effect of group (F(2,59)=4.8, p=0.01, ɛ=0.467), with significantly lower amplitudes in non-medicated patients with respect to both the control and medicated groups (MD=1.19, p=0.01, MD=1.27, p=0.005, respectively). There were no significant differences in the latencies of any of the waves among the groups. The main finding of this study was the reduction in the IA in early PD. Reorientation of attention (RON) showed a dopaminergic modulation in these patients. These results represent the basis for future in depth studies on the involvement of IA in executive impairments in PD.