Event-related potentials by word repetition in aging and Parkinson's disease

Background. Although memory tested explicitly is impaired in normal aging and Parkinson's disease (PD), it is less clear if memory tested implicitly is similarly affected. To assess this, event-related potentials (ERPs) were recorded during a word-repetition paradigm. Methods. The ERPs were recorded from 17 young and 14 old control subjects and 21 patients with nondemented PD as they listened to word or pronounceable nonword lists. Words were repeated at intervals of 0, 5 and 11-77 intervening items. The subjects were required to push a button in response to occasional nonwords. Results. The mean N400 amplitude for the first presentation of words was reduced in patients with PD as compared to both control groups, but no difference between the two control groups was observed. In both control groups, the N400 was attenuated for repeated words, and the attenuation was more pronounced for immediate than for both delayed repetitions. In patients with PD, the attenuation was noted only for immediate repetition. Conclusion. To the extent that the ERP repetition effect recorded during this repetition priming paradigm is a measure of implicit performance, the data suggest that implicit memory is impaired in PD patients, but preserved in normal aging.