The vestibular system does not modulate fusimotor drive to muscle spindles in contracting leg muscles of seated subjects

L. R. Bent, M. Sander, P. S. Bolton, V. G. Macefield

    Research output: Contribution to journalArticlepeer-review

    Abstract

    We previously showed that sinusoidal galvanic vestibular stimulation (GVS) does not modulate the firing of spontaneously active muscle spindles in relaxed human leg muscles. However, given that there is little, if any, fusimotor drive to relaxed human muscles, we tested the hypothesis that vestibular modulation of muscle spindles becomes apparent during volitional contractions at levels that engage the fusimotor system. Unitary recordings were made from 28 muscle spindle afferents via tungsten microelectrodes inserted percutaneously into the common peroneal nerve of seated awake human subjects. Twenty-one of the spindle afferents were spontaneously active at rest and each increased its firing rate during a weak static contraction; seven were silent at rest and were recruited during the contraction. Sinusoidal bipolar binaural galvanic vestibular stimulation (±2 mA, 100 cycles) was applied to the mastoid processes at 0.8 Hz. This continuous stimulation produced a sustained illusion of "rocking in a boat" or "swinging in a hammock" but no entrainment of EMG. Despite these robust vestibular illusions, none of the fusimotor-driven muscle spindles exhibited phase-locked modulation of firing during sinusoidal GVS. We conclude that this dynamic vestibular input was not sufficient to modulate the firing of fusimotor neurones recruited during a voluntary steady-state contraction, arguing against a significant role of the vestibular system in adjusting the sensitivity of muscle spindles via fusimotor neurones.
    Original languageEnglish
    Pages (from-to)175-183
    Number of pages9
    JournalExperimental Brain Research
    Volume227
    Issue number2
    DOIs
    Publication statusPublished - 2013

    Fingerprint

    Dive into the research topics of 'The vestibular system does not modulate fusimotor drive to muscle spindles in contracting leg muscles of seated subjects'. Together they form a unique fingerprint.

    Cite this