Cognitive event-related potentials: Longitudinal changes in mild cognitive impairment

Objective: To measure changes over time in the latency and amplitude of the major waves of auditory event-related potentials (AERP) and their correlation with the memory status of patients with mild cognitive impairment (MCI). Methods: AERPs were recorded in 22 MCI patients (mean +/- SD age = 67.4 +/- 7.8, median (interquartile range-IQR) MMSE score = 28 (27-29) in three consecutive exams and in 30 age-matched controls at baseline. During this time period, 3 patients converted to Alzheimer disease (AD). Latencies and amplitudes of N200, P300 and Slow Wave and the N200-P300 peak-to-peak amplitudes and latencies were determined, and correlation coefficients (CC) between them and MMSE scores were calculated. Results: A significant increase in the P300 latency and a decrease in the N200 amplitude were observed between the exams. Only N200 latency correlated with baseline MMSE scores, whereas P300 and Slow Wave latencies correlated with age. Conclusions: N200 amplitude is more sensitive in identifying differences over time at the early stages of the disease, whereas P300 latency at later stages. Significance: A new N2-P3 inter-peak index that incorporates changes in N200 and P300 latencies and amplitudes into a single parameter is introduced in order to adequately describe the gradual progress of MCI and its transition to AD. (C) 2010 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.