Citation

Dakin CJ, Heroux ME, Luu BL, Inglis JT, Blouin JS. J. Neurophysiol. 2015; 115(3): 1289-1297.

Affiliation

University of British Columbia jsblouin@interchange.ubc.ca.

Copyright

(Copyright © 2015, American Physiological Society)

DOI

10.1152/jn.00512.2015

PMID

26683068

Abstract

The soleus (Sol) and medial gastrocnemius (mGas) muscles have different patterns of activity during standing balance and may have distinct functional roles. Using surface electromyography we previously, observed larger responses to galvanic vestibular stimulation (GVS) in the mGas compared to the Sol muscle. However, it is unclear whether this difference is an artifact that reflects limitations associated with surface electromyography recordings or whether a compensatory balance response to a vestibular error signal activates the mGas to a greater extent than the Sol. In the present study, we compared the effect of GVS on the discharge behaviour of nine Sol and twenty-one mGas motor units from freely standing subjects. In both Sol and mGas motor units, vestibular stimulation induced biphasic responses in measures of discharge timing (11 ± 5.0 [mGas] and 5.6 ± 3.8 [Sol] counts relative to the sham (mean ± standard deviation)), and frequency (0.86 ± 0.6 Hz [mGas], 0.34 ± 0.2 Hz [Sol] change relative to the sham). Peak-to-trough response amplitudes were significantly larger in the mGas (62% in the probability-based measure and 160% in the frequency-based measure) compared to the Sol (multiple p < 0.05). Our results provide direct evidence that vestibular signals have a larger influence on the discharge activity of motor units in the mGas compared to the Sol. More tentatively, these results indicate the mGas plays a greater role in vestibular-driven balance corrections during standing balance.

Language: en