Component activities in the autoregressive activity of physiological systems.

The higher-order autoregressive (AR) activity of a physiological system (Sato 1975a,b; Sato et al., 1977) was decomposed into first- and second-order activities. The former time-pattern displays a fast rise and an exponential decay, while the latter exhibits a damped sine wave. Application of this component analysis to EEG showed the first-order activity to coincide with the nonoscillatory delta component. The frequency distribution of the natural, damped and resonance frequencies of the second-order activities was found to show one, two or three modes in each frequency range of the delta, theta and beta rhythms in ninety normal adult EEGs. Hence, the second-order activities agree with the oscillatory delta, theta, alpha and beta rhythms. Some changes were induced not only in the frequency of theta and beta rhythms but also in that of alpha rhythm by over-breathing for about three minutes.