Noise Can Improve Human Balance Control

Noise can improve human balance control, to the point that it may enable elderly subjects to steady themselves as well as their young counterparts, researchers in New England have demonstrated (Jim Collins, Boston University, 617-353-0390, jcollins@bu.edu). Noise, in this case, refers to random mechanical vibrations applied to the feet.

In physics, noise denotes any random or seemingly useless fluctuation. Static on a radio station, peripheral conversations in a crowded room, and flashing neon lights along a busy thoroughfare all tend to obscure or distract one from receiving the desired information.

But more and more studies in a wide variety of systems---global climate models, electronic circuits and sensory neurons, to name a few---have shown that certain levels of noise can actually enhance the detection and transmission of weak signals, through a mechanism known as stochastic resonance (SR).

Here the authors show that postural sway, the slight movements exhibited by the body when it is erect, can be significantly reduced for both young and elderly individuals. The authors achieved this by randomly applying subtle mechanical vibrations, just below the threshold of sensory perception, under the subjects' feet. The random vibrations likely act to enhance the sensation of pressure on the soles of the feet.

The authors further demonstrate a trend in elderly subjects towards reducing their postural sway to the level of young subjects, suggesting that noise may be a "fountain of youth" for human balance.

These results indicate that the random vibrations may ameliorate age-related impairments in balance control. Noise may provide similar beneficial effects in individuals with marked sensory deficits, such as patients who have suffered a stroke or a disorder in the peripheral nervous system.

In the future, the authors speculate, noise-based devices, such as randomly vibrating shoe inserts, may enable people to overcome functional difficulties due to age- or disease-related sensory loss (Priplata et al., Physical Review Letters, 2 December 2002).

This paper comes on the heels of another recent finding, that the random hand motions generated by noise in the human nervous system make it possible for people to balance a stick on a finger (Cabrera and Milton, Physical Review Letters, 7 October).