No abstract

This work indicates that noise-based devices could ameliorate diabetic and stroke impairments in balance control.

Noise can enhance the detection and transmission of weak signals in certain nonlinear systems, via a mechanism known as stochastic resonance. Here we show that input noise can be used to improve motor control in humans. Specifically, we show that the postural sway of both young and elderly individuals during quiet standing can be significantly reduced by applying subsensory mechanical noise to the feet. We further demonstrate with input noise a trend towards the reduction of postural sway in elderly subjects to the level of young subjects. These results suggest that noise-based devices, such as randomly vibrating shoe inserts, may enable people to overcome functional difficulties due to age-related sensory loss.

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.The development of predictive tests for falls, a major cause of disability and death in older individuals, is a challenging and important task. Postural instability in elderly people and in patients with certain pathologies [1-5] is a major contributor to such falls. Recently, a novel intervention [6][7][8][9][10] was proposed to increase postural stability that is based on the principle of stochastic resonance -enhancing signal transmission by introducing noise into the system. The search for new therapeutic interventions designed to improve postural stability underscores the need to develop reliable non-invasive methods to test for beneficial effects.Previous studies [11][12][13][14] have shown that the time series generated by a variety of free-running healthy physiologic dynamics exhibit complex fluctuations that are not simply due to uncorrelated random errors. This is also true for physiologic systems whose main purpose seem to be reducing variability and maintaining a steady state, as for example, the postural control system [15]. Previous studies [16] suggested 1 that the complex fluctuations in the time series 1 Previous studies [16] of postural control in humans using stabilogram-diffusion analysis indicate that over time intervals shorter than approximately one second, the body sways as a positively correlated random walk, while over larger time intervals it resembles a negatively correlated random walk. The purpose of this study is to quantify the complex dynamics of postural control in healthy subjects and compare these dynamics to those from elderly people at risk of falls. Furthermore, we purpose to determine whether loss of postural complexity is reversible through a noisebased intervention aimed at enhancing sensory feedback from the feet. NIH Public AccessWe assume that the postural regulatory mechanisms control two fundamental variables related to balance: the position of the center of pressure and the velocity at which the center of pressure changes its position.Accordingly, to probe the dynamical properties of postural control, we quantify the complex variability of the COP position and velocity time series for both the anteroposterior (AP) and mediolateral (ML) directions. F...