Noise and poise: Enhancement of postural complexity in the elderly with a stochastic-resonance-based therapy

Abstract

Pathologic states are associated with a loss of dynamical complexity. Therefore, therapeutic interventions that increase physiologic complexity may enhance health status. Using multiscale entropy analysis, we show that the postural sway dynamics of healthy young and healthy elderly subjects are more complex than that of elderly subjects with a history of falls. Application of subsensory noise to the feet has been demonstrated to improve postural stability in the elderly. We next show that this therapy significantly increases the multiscale complexity of sway fluctuations in healthy elderly subjects. Quantification of changes in dynamical complexity of biologic variability may be the basis of a new approach to assessing risk and to predicting the efficacy of clinical interventions, including noise-based therapies.

Fig. 1

(Colour on-line) Time series of the center of pressure displacement (left panels) and velocity (right panels) in the anteroposterior direction for representative: healthy young (top panels), healthy elderly (middle panels) and elderly faller (bottom panels) subjects. For each displacement time series the trends obtained by summing the 5 intrinsic mode functions of lowest frequency are shown in red in the on-line version (see appendix.)

Fig. 2

MSE analysis of: A) anteroposterior and B) mediolateral postural displacement sway time series recorded under free-running (control) conditions and with subsensory noise stimulation (stimulus) from a healthy elderly subjects. Time series were detrended using the empirical mode decomposition method. The symbols represent mean values of sample entropy (SampEn) for all subjects and all trials and error bars represent standard errors. Parameters for the calculation of SampEn were: m=2 and r=0.15.