title: Vestibular stimulation-induced facilitation of cervical premotoneuronal systems in humans.
abstract: It is unclear how descending inputs from the vestibular system affect the excitability of cervical interneurons in humans. To elucidate this, we investigated the effects of galvanic vestibular stimulation (GVS) on the spatial facilitation of motor-evoked potentials (MEPs) induced by combined pyramidal tract and peripheral nerve stimulation. To assess the spatial facilitation, electromyograms were recorded from the biceps brachii muscles (BB) of healthy subjects. Transcranial magnetic stimulation (TMS) over the contralateral primary motor cortex and electrical stimulation of the ipsilateral ulnar nerve at the wrist were delivered either separately or together, with interstimulus intervals of 10 ms (TMS behind). Anodal/cathodal GVS was randomly delivered with TMS and/or ulnar nerve stimulation. The combination of TMS and ulnar nerve stimulation facilitated BB MEPs significantly more than the algebraic summation of responses induced separately by TMS and ulnar nerve stimulation (i.e., spatial facilitation). MEP facilitation significantly increased when combined stimulation was delivered with GVS (p < 0.01). No significant differences were found between anodal and cathodal GVS. Furthermore, single motor unit recordings showed that the short-latency excitatory peak in peri-stimulus time histograms during combined stimulation increased significantly with GVS. The spatial facilitatory effects of combined stimulation with short interstimulus intervals (i.e., 10 ms) indicate that facilitation occurred at the premotoneuronal level in the cervical cord. The present findings therefore suggest that GVS facilitates the cervical interneuron system that integrates inputs from the pyramidal tract and peripheral nerves and excites motoneurons innervating the arm muscles.
authors.affiliation: Department of Integrative Physiology, Kyorin University School of Medicine, Mitaka City, Tokyo, Japan.|Division of Health and Sports Education, The United Graduate School of Education, Tokyo Gakugei University, Koganei City, Tokyo, Japan.
authors.forename: Shinya
authors.initials: S
authors.lastname: Suzuki
authors.affiliation: Department of Integrative Physiology, Kyorin University School of Medicine, Mitaka City, Tokyo, Japan.
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Nakajima
authors.affiliation: Department of Integrative Physiology, Kyorin University School of Medicine, Mitaka City, Tokyo, Japan.
authors.forename: Shun
authors.initials: S
authors.lastname: Irie
authors.affiliation: Department of Integrative Physiology, Kyorin University School of Medicine, Mitaka City, Tokyo, Japan.
authors.forename: Ryohei
authors.initials: R
authors.lastname: Ariyasu
authors.affiliation: Division of Health and Sports Education, The United Graduate School of Education, Tokyo Gakugei University, Koganei City, Tokyo, Japan.|Division of Health and Sports Sciences, Faculty of Education, Chiba University, Chiba City, Chiba, Japan.
authors.forename: Tomoyoshi
authors.initials: T
authors.lastname: Komiyama
authors.affiliation: Department of Integrative Physiology, Kyorin University School of Medicine, Mitaka City, Tokyo, Japan.
authors.forename: Yukari
authors.initials: Y
authors.lastname: Ohki
mesh_terms: D000328:Adult; D002574:Cervical Vertebrae / Q000502:physiology*; D004558:Electric Stimulation; D004576:Electromyography; D005260:Female; D006801:Humans; D008297:Male; D009046:Motor Neurons / Q000502:physiology*; D050781:Transcranial Magnetic Stimulation; D014722:Vestibule, Labyrinth / Q000502:physiology*; D055815:Young Adult