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Experimental Brain Research

, Volume 217, Issue 2, pp 175–186 | Cite as

Imperceptible electrical noise attenuates isometric plantar flexion force fluctuations with correlated reductions in postural sway

  • Fernando Henrique MagalhãesEmail author
  • André Fabio Kohn
Original Article

Abstract

Optimal levels of noise stimulation have been shown to enhance the detection and transmission of neural signals thereby improving the performance of sensory and motor systems. The first series of experiments in the present study aimed to investigate whether subsensory electrical noise stimulation applied over the triceps surae (TS) in seated subjects decreases torque variability during a force-matching task of isometric plantar flexion and whether the same electrical noise stimulation decreases postural sway during quiet stance. Correlation tests were applied to investigate whether the noise-induced postural sway decrease is linearly predicted by the noise-induced torque variability decrease. A second series of experiments was conducted to investigate whether there are differences in torque variability between conditions in which the subsensory electrical noise is applied only to the TS, only to the tibialis anterior (TA) and to both TS and TA, during the force-matching task with seated subjects. Noise stimulation applied over the TS muscles caused a significant reduction in force variability during the maintained isometric force paradigm and also decreased postural oscillations during quiet stance. Moreover, there was a significant correlation between the reduction in force fluctuation and the decrease in postural sway with the electrical noise stimulation. This last result indicates that changes in plantar flexion force variability in response to a given subsensory random stimulation of the TS may provide an estimate of the variations in postural sway caused by the same subsensory stimulation of the TS. We suggest that the decreases in force variability and postural sway found here are due to stochastic resonance that causes an improved transmission of proprioceptive information. In the second series of experiments, the reduction in force variability found when noise was applied to the TA muscle alone did not reach statistical significance, suggesting that TS proprioception gives a better feedback to reduce force fluctuation in isometric plantar flexion conditions.

Keywords

Stochastic resonance Postural control Somatosensation Posture stabilization Force steadiness Torque variability 

Abbreviations

ANOVA

Analysis of variance

AP

Anterior–posterior

COP

Center of pressure

COPap

COP in the anterior–posterior axis

COPml

COP in the medio-lateral axis

ML

Medio-lateral

MVC

Maximal voluntary contraction

N

Newton(s)

OS

Optimal stimulation

RMS

Root-mean square

RMSap

COPap RMS

RMSml

COPml RMS

SD

Standard deviation

ST

Sensory threshold

TA

Tibialis anterior

TS

Triceps surae

VMap

COPap velocity

VMml

COPml velocity

Notes

Acknowledgments

This research was funded by CNPq. The first author is a recipient of a fellowship from FAPESP, grant #2011/13222-6. We are grateful to Sandro A. Miqueleti for his invaluable technical support, and we thank Dr. Rinaldo A. Mezzarane for his useful comments.

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Copyright information

© Springer-Verlag 2011

Authors and Affiliations

  • Fernando Henrique Magalhães
    • 1
    Email author
  • André Fabio Kohn
    • 1
  1. 1.Neuroscience Program and Biomedical Engineering LaboratoryUniversidade de São Paulo, EPUSP, PTCSão PauloBrazil

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