High internight reliability of computer-measured NREM delta, sigma, and beta: Biological implications

Background: Computer analysis of the sleep electroencephalogram (EEG) wavef orms is widely employed, but there have been no systematic studies of its r eliability. Methods: The most commonly used computer methods are power spectral analysi s with the fast-Fourier transform (FFT) and period amplitude analysis (PAA) with zero cross or zero first derivative half-wave measurement. We applied all three computer methods to the digitized EEG of 16 normal subjects who underwent 5 consecutive nights of baseline (placebo) recording. We evaluate d the internight reliability, of three non-rapid eye movement (NREM) freque ncy bands of special importance to sleep research: delta (0.3-3 Hz), sigma (12-15 Hz), and beta (15-23 Hz). Results: Both FFT and the two methods of PAA gave excellent internight reli ability for delta and sigma. Even a single night of recording correlated hi ghly (r > .9) with the 5-night mean. Beta reliability was lower but still h ighly significant for both the PAA and the FFT measures. Conclusions: Computer-analyzed sleep EEG data are highly reliable. Period a mplitude methods demonstrate that wave incidence and period as well as ampl itude are reliable, indicating that the reliability of composite measures ( FFT power, PAA integrated amplitude) is not solely based on individual diff erences in EEG amplitude. The high internight stability of NREM delta indic ates that it possesses traitlike characteristics and is relatively independ ent of day-to-day variations in state. (C) 2000 Society of Biological Psych iatry.