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This Article Full Text Full Text (PDF) All Versions of this Article: 583/3/1117    most recent jphysiol.2007.133264v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Dakin, C. J. Articles by Blouin, J.-S. Search for Related Content PubMed PubMed Citation Articles by Dakin, C. J. Articles by Blouin, J.-S. Related Collections Integrative

¹ School of Human Kinetics
² Brain Research Centre
³ International Collaboration on Repair Discoveries, Univeristy of British-Columbia, British Columbia, Canada

Stochastic vestibular stimulation (SVS) can be used to study the postural responses to unpredictable vestibular perturbations. The present study seeks to determine if stochastic vestibular stimulation elicits lower limb muscular responses and to estimate the frequency characteristics of these vestibulo-motor responses in humans. Fourteen healthy subjects were exposed to unpredictable galvanic currents applied on their mastoid processes while quietly standing (±3 mA, 0–50 Hz). The current amplitude and stimulation configuration as well as the subject's head position relative to their feet were manipulated in order to determine that: (1) the muscle responses evoked by stochastic currents are dependent on the amplitude of the current, (2) the muscle responses evoked by stochastic currents are specific to the percutaneous stimulation of vestibular afferents and (3) the lower limb muscle responses exhibit polarity changes with different head positions as previously described for square-wave galvanic vestibular stimulation (GVS) pulses. Our results revealed significant coherence (between 0 and 20 Hz) and cumulant density functions (peak responses at 65 and 103 ms) between SVS and the lower limbs' postural muscle activity. The polarity of the cumulant density functions corresponded to that of the reflexes elicited by square-wave GVS pulses. The SVS–muscle activity coherence and time cumulant functions were modulated by current amplitude, electrode position and head orientation with respect to the subject's feet. These findings strongly support the vestibular origin of the lower limb muscles evoked by SVS. In addition, specific frequency bandwidths in the stochastic vestibular signal contributed to the early (12–20 Hz) and late components (2–10 Hz) of the SVS-evoked muscular responses. These frequency-dependent SVS-evoked muscle responses support the view that the biphasic muscle response is conveyed by two distinct physiological processes.

(Received 23 March 2007; accepted after revision 13 July 2007; first published online 19 July 2007)
Corresponding author J.-S. Blouin: 210-6081 University Boulevard, University of British-Columbia, Vancouver, British Columbia, Canada V6T1Z1. Email: jsblouin{at}interchange.ubc.ca

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