Age-related changes of cognitive brain function are reflected by neurophysiological measurements such as quantitative electroencephalograms (EEG) and event -related potentials (ERP). However, longitudinal changes in these neurophysiological parameters in healthy elderly individuals have remained largely unreported. In the present study, quantitative EEG and ERP were measured prospectively twice, at an interval of 4 years, in 21 physically and cognitively healthy geriatric volunteers (age at first session, 66.3 ± 2.6 years). EEG data collected from 18 electrode sites on the cranial surface according to the 10-20 International System were used for quantitative analysis of waveform recognition for 1 mm under resting, awake, eyes-closed conditions. ERPs were elicited using an auditory oddball paradigm. With each subject, we compared EEG and ERP data obtained at the 2 sessions. The 4-year follow-up of quantitative BEG revealed a significant increase in the incidence of Qθ1 band waves and a significant decrease in the incidence of α2 band waves at nearly all sites. Although no changes in P300 amplitudes were observed, P300 latencies were significantly increased at the 2^ session at all sites, with mean prolongation of 4.7 ± 0.7 ms/year. These results are consistent with those of previous cross-sectional studies, and provide the first prospective demonstration of subtle slowing of cognitive processes in normal elderly subjects
