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Vestibular stimulation-induced facilitation of cervical premotoneuronal systems in humans

View Article: PubMed Central - PubMed

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.

No MeSH data available.


The effects of galvanic vestibular stimulation (GVS) on ulnar nerve-induced facilitation of motor-evoked potentials in a single subject.Full-wave rectified and averaged electromyograms (EMGs) in the biceps brachii (BB) muscle after separate ulnar nerve stimulation (NERVE) at 1.0 × the motor threshold of the first dorsal interosseous muscle (A, E, I), separate transcranial magnetic stimulation (TMS) over the contralateral primary motor cortex at 1.1 × the active motor threshold of the BB (B, F, J), and the combination (COMB) of NERVE and TMS (C, G, K). These waveforms were obtained without GVS (left panels), during anodal GVS (middle panels), and during cathodal GVS (right panels) at 2.0 × the perceptual threshold of the head sway. The grey waveforms in C, G, and K represent the summation (SUM) of the averaged EMG waveforms after separate TMS and NERVE. The waveforms in D, H, and L represent the COMB waveforms with the SUM waveforms subtracted.
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pone.0175131.g003: The effects of galvanic vestibular stimulation (GVS) on ulnar nerve-induced facilitation of motor-evoked potentials in a single subject.Full-wave rectified and averaged electromyograms (EMGs) in the biceps brachii (BB) muscle after separate ulnar nerve stimulation (NERVE) at 1.0 × the motor threshold of the first dorsal interosseous muscle (A, E, I), separate transcranial magnetic stimulation (TMS) over the contralateral primary motor cortex at 1.1 × the active motor threshold of the BB (B, F, J), and the combination (COMB) of NERVE and TMS (C, G, K). These waveforms were obtained without GVS (left panels), during anodal GVS (middle panels), and during cathodal GVS (right panels) at 2.0 × the perceptual threshold of the head sway. The grey waveforms in C, G, and K represent the summation (SUM) of the averaged EMG waveforms after separate TMS and NERVE. The waveforms in D, H, and L represent the COMB waveforms with the SUM waveforms subtracted.

Mentions: Fig 3 illustrates the effects of GVS on the ulnar nerve-conditioned BB MEPs in a single subject. In the control condition, TMS with ulnar nerve stimulation resulted in facilitation of the MEPs (Fig 3C) compared with TMS alone (Fig 3B). Importantly, the facilitatory effects of the combined stimulation were larger than the summation of the effects of the separate stimuli (i.e., TMS alone and ulnar nerve stimulation alone) (grey waveform in Fig 3C), which indicated extra-facilitation effects (downward arrow in Fig 3D). The facilitatory effects of the combined stimulation were markedly augmented in both the anodal and cathodal GVS conditions with respect to the control condition (Fig 3G and 3K, see also 3H and 3L).


Vestibular stimulation-induced facilitation of cervical premotoneuronal systems in humans
The effects of galvanic vestibular stimulation (GVS) on ulnar nerve-induced facilitation of motor-evoked potentials in a single subject.Full-wave rectified and averaged electromyograms (EMGs) in the biceps brachii (BB) muscle after separate ulnar nerve stimulation (NERVE) at 1.0 × the motor threshold of the first dorsal interosseous muscle (A, E, I), separate transcranial magnetic stimulation (TMS) over the contralateral primary motor cortex at 1.1 × the active motor threshold of the BB (B, F, J), and the combination (COMB) of NERVE and TMS (C, G, K). These waveforms were obtained without GVS (left panels), during anodal GVS (middle panels), and during cathodal GVS (right panels) at 2.0 × the perceptual threshold of the head sway. The grey waveforms in C, G, and K represent the summation (SUM) of the averaged EMG waveforms after separate TMS and NERVE. The waveforms in D, H, and L represent the COMB waveforms with the SUM waveforms subtracted.
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC5384664&req=5

pone.0175131.g003: The effects of galvanic vestibular stimulation (GVS) on ulnar nerve-induced facilitation of motor-evoked potentials in a single subject.Full-wave rectified and averaged electromyograms (EMGs) in the biceps brachii (BB) muscle after separate ulnar nerve stimulation (NERVE) at 1.0 × the motor threshold of the first dorsal interosseous muscle (A, E, I), separate transcranial magnetic stimulation (TMS) over the contralateral primary motor cortex at 1.1 × the active motor threshold of the BB (B, F, J), and the combination (COMB) of NERVE and TMS (C, G, K). These waveforms were obtained without GVS (left panels), during anodal GVS (middle panels), and during cathodal GVS (right panels) at 2.0 × the perceptual threshold of the head sway. The grey waveforms in C, G, and K represent the summation (SUM) of the averaged EMG waveforms after separate TMS and NERVE. The waveforms in D, H, and L represent the COMB waveforms with the SUM waveforms subtracted.
Mentions: Fig 3 illustrates the effects of GVS on the ulnar nerve-conditioned BB MEPs in a single subject. In the control condition, TMS with ulnar nerve stimulation resulted in facilitation of the MEPs (Fig 3C) compared with TMS alone (Fig 3B). Importantly, the facilitatory effects of the combined stimulation were larger than the summation of the effects of the separate stimuli (i.e., TMS alone and ulnar nerve stimulation alone) (grey waveform in Fig 3C), which indicated extra-facilitation effects (downward arrow in Fig 3D). The facilitatory effects of the combined stimulation were markedly augmented in both the anodal and cathodal GVS conditions with respect to the control condition (Fig 3G and 3K, see also 3H and 3L).

View Article: PubMed Central - PubMed

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.

No MeSH data available.