Simultaneously evoked primary and cognitive visual evoked potentials reveal visuocognitive dysfunction in younger patients with Parkinson's Disease

A study of primary (VEPs) and cognitive (ERPs) visual evoked potentials was carried out in a group of non-demented AfroAmerican Parkinson's Disease (PD) patients. Two horizontal sinusoidal gratings differing in spatial frequency, i.e., 1 and 4 cycles per degree (cpd), were presented in an odd-ball paradigm to 17 patients with PD and 17 age-matched control subjects. Differently from 1 cpd pattern stimulus, unable to reveal primary visual defects, the 4 cpd one may give direct information on both retinal and cognitive visual deficits. We measured the latencies and amplitudes of N70, PI 00 and P300 components, and derived the normalized measures of P300-N70 latency difference (Central Processing Time - CPT70), the P300-P100 latency difference (CPT100) and the P300 amplitude responses normalized to either N70 and PI 00 amplitude (Amplitude Ratios AR70 and AR 100). The results confirm in a non Caucasian population that absolute and normalized ERP amplitude and latency abnormalities are a distinguishing feature of younger PD patients from controls, hi particular PSOO measures are abnormal for 1 cpd pattern. A negative correlation exists between P300 amplitude and the motor score. By comparing the results for 1 and 4 cpd stimuli it can be concluded that primary and cognitive visual abnormalities are independently affected in PD, implying that visuo-cognitive abnormalities are not passively determined by retinal dopaminergic deficiency.