What is the substrate of 1/f fluctuations in biological signals?

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1.By surveying the previously observed 1/f fluctuations in biological signals, the following diverse biological signals had been found to exhibit 1/f fluctuations. At cell level, spontaneous neuronal discharge, impulse propagation on axon, single neuronal activity during rapid eye movement(REM)sleep in cat's brain.At level of organ, heart rate variability, blood pressure, respiration rhythm, pupil diameter and focus control, autonomic nerve activity, fluctuations in frequency of alpha wave. At behavior level, body sway, clapping ryhthm. Power spectral densities of 1/f profile were widely ranged from 10^<-5> to 10Hz.2.One of the most important properties of 1/f fluctuations is the lower limit frequency of 1/f spectral profile. Concerning human heart rate variability, 1/f spectral profile is empirically known to be extended from 10^<-1> to 10^<-4> or 10^<-5>Hz, where 10^<-5>Hz roughly corresponds to time scale of a day. In this study, the long-term recordings of cat's heart rate variabil … More ity was mainly performed.3.With special preparation in which the recording electrodes were directly attached to cat's heart, continuous recordings during four days were carried out three times successfully. These experiments confirmed that 1/f spectral profiles are observed down to 10^<-4>Hz. Besides, continuous recordings during 6days(144hr)showed the flat profile in the frequency tends to exist from 10^<-4> to 10^<-5>Hz. This weakened power in the lower frequency range is expected to come from the suppression of cat's behavior within the cage of limited extent.4.Concerning the single neuronal activities in cat's brain, their 1/f fluctuations during REM sleep were shown to be consistent through episodes. The physiologically realistic generation mechanism could be explained by the Hopfieldtype interconnected neural network model under global inhibitory input. On the other hand, the mathematical interpretation of 1/f fluctuation as a stochastic process was newly proposed, which could be a theoretical basis of numerical analyzes of 1/f fluctuations. Less