What is physiologic complexity and how does it change with aging and disease?

Complexity Analysis of Spontaneous Brain Activity in Attention-Deficit/Hyperactivity Disorder: Diagnostic Implications

“…This latter study is a precedent of our current investigation since AD patients exhibited a significantly reduced pattern of LZC, supporting Goldberger's theory of complexity loss in aging and disease (20). Moreover, recent studies have shown that LZC is related to the average information quantity in a signal as well as signal characteristics like spectral bandwidth and harmonic variability (26).…”

“…Parameters of EEG-MEG complexity usually estimate the predictability of brain oscillations and/or the number of independent oscillators underlying the observed signals (19,20). Among those, LZC is a model-independent estimator of system complexity adequately suited for the analysis of biomedical signals (21).…”

The effect of footwear on postural control in bipedal quiet stance

“…This paradigm suggest that a decrease in the system complexity may be an indication of a decrease in the system's ability to cope with perturbations, hence leading to a less stable situation and to a higher risk of fall (Lipsitz and Goldberger 1992, Goldberger et al 2001, Vaillancourt and Newell 2002, Cavanaugh, J.T., Guskiewicz K.M., Stergiou N., 2005, Hong 11 2008. Newell (1998) proposed to interpret the "complexity of the postural control system" in the context of Bernstein's degree of freedom problem (Bernstein, N., 1967) in the sense that a more complex system would be characterized by having more degrees of freedom and thus more states available, whereas a less complex system is characterized by fewer degrees of freedom and thus fewer accessible states.…”

Approximate entropy and auto mutual information analysis of the electroencephalogram in Alzheimer’s disease patients

“…A complexity measure should vanish for both completely regular and completely random system [9], something that does not happen with ApEn [19]. Moreover, a steeper decline of the AMI for a given time series does not necessarily point out that physiologic or physical complexity has increased, as it may be related to a breakdown in multiscale correlations or to more subtle alterations in non-linear control [16]. The negative relationship in the correlation between both metrics (as shown in Figure 2) is due to the fact that, while ApEn values are positive and larger in more irregular time series, the more negative AMI rates of decrease are associated with higher irregularity.…”