Internight reliability and benchmark values for computer analyses of non-rapid eye movement (NREM) and REM EEG in normal young adult and elderly subjects

Objective: To determine the reliability of computer measured non-rapid eye movement (NREM) and REM frequency bands in the 0.3-45 Hz range and to provi de benchmark data for these measures in young normal (YN) and elderly norma l (EN) subjects (Ss). Methods: Sleep EEG was recorded in 19 YN and 19 EN Ss on 4 non-consecutive baseline nights and simultaneously quantified as fast Fourier transform (FF T) power and 3 zero-cross period-amplitude (PA) measures: integrated amplit ude, time in band and average wave amplitude. Results: The shapes of both the FFT and PA spectra differed among Ss but we re highly consistent within individuals. Inter-night reliability of the sep arate frequency bands was correspondingly high. Despite substantial age eff ects, the reliability of computer-measured Sleep EEG in the elderly equaled that of the YN Ss. Within both the YN and EN groups, the shapes of the NRE M and REM spectral curves differed significantly. The NREM and REM also dif fered significantly in them two age groups. Conclusions. Computer-measured sleep EEG is highly reliable across non-cons ecutive nights in both young and elderly normal Ss. The trait-like stabilit y of these measures suggests they are genetically determined. This possibil ity is supported by twin study data that show strong heritability for FFT-m easured waking EEG. The different shapes of NREM and REM spectra add furthe r evidence that these are fundamentally different states of brain organizat ion. The age differences in spectral shape, along with PA data for wave inc idence, demonstrate that age effects on sleep EEG are not caused by changes in skull impedance or other non-cerebral factors. (C) 2001 Elsevier Scienc e Ireland Ltd. All rights reserved.