Limits...
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.


Related in: MedlinePlus

The effects of galvanic vestibular stimulation (GVS) on the firing probability of single motor units (MUs) after combined motor cortex and ulnar nerve stimulation.A–H show the peristimulus time histograms (PSTHs) of a single MU in the biceps brachii (BB) muscle after separate ulnar nerve stimulation (NERVE) at 1.0 × motor threshold (MT) of the first dorsal interosseous muscle (A, E), separate transcranial magnetic stimulation (TMS) (B, F) over the contralateral primary motor cortex at 1.25 × active motor threshold of the BB, and combined stimulation (COMB) (C, G) in the control (A–D) and anodal GVS conditions (E–H). Each PSTH was obtained after 50 stimuli. The counts in these PSTHs were subtracted by the mean counts during a 50 ms prestimulus period. D and H show differential PSTHs after subtraction of the summed PSTHs after separate stimuli from the PSTHs of the COMB. The number of counts in each bin was normalized by the number of triggers. The vertical dashed line represents the onset of the excitatory peak in the PSTH after separate TMS. The superimposed waveforms in the upper right corner of each PSTH show the MU action potentials (n = 50) obtained from each stimulus trial. I–L indicate the peak counts of the MU firings in the differential PSTHs in the control and anodal GVS conditions obtained from 31 MUs that were investigated with the NERVE set at 1.0 × MT (I, J) and 20 MUs that were investigated with the NERVE set at 0.75 × MT (K, L). The error bars represent 1 standard deviation. The analysis window was set at a predefined period (1.0 ms duration) that started 1.0 ms after the onset of the TMS-induced excitatory peak in the PSTH. **p < 0.01.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC5384664&req=5

pone.0175131.g005: The effects of galvanic vestibular stimulation (GVS) on the firing probability of single motor units (MUs) after combined motor cortex and ulnar nerve stimulation.A–H show the peristimulus time histograms (PSTHs) of a single MU in the biceps brachii (BB) muscle after separate ulnar nerve stimulation (NERVE) at 1.0 × motor threshold (MT) of the first dorsal interosseous muscle (A, E), separate transcranial magnetic stimulation (TMS) (B, F) over the contralateral primary motor cortex at 1.25 × active motor threshold of the BB, and combined stimulation (COMB) (C, G) in the control (A–D) and anodal GVS conditions (E–H). Each PSTH was obtained after 50 stimuli. The counts in these PSTHs were subtracted by the mean counts during a 50 ms prestimulus period. D and H show differential PSTHs after subtraction of the summed PSTHs after separate stimuli from the PSTHs of the COMB. The number of counts in each bin was normalized by the number of triggers. The vertical dashed line represents the onset of the excitatory peak in the PSTH after separate TMS. The superimposed waveforms in the upper right corner of each PSTH show the MU action potentials (n = 50) obtained from each stimulus trial. I–L indicate the peak counts of the MU firings in the differential PSTHs in the control and anodal GVS conditions obtained from 31 MUs that were investigated with the NERVE set at 1.0 × MT (I, J) and 20 MUs that were investigated with the NERVE set at 0.75 × MT (K, L). The error bars represent 1 standard deviation. The analysis window was set at a predefined period (1.0 ms duration) that started 1.0 ms after the onset of the TMS-induced excitatory peak in the PSTH. **p < 0.01.

Mentions: Fig 5A–5H illustrate the PSTHs of a single MU in the control and anodal GVS conditions. In the control condition, combined TMS (1.25 × AMT) and ulnar nerve stimulation (1.0 × MT) produced a slight increase in firing probability at a short latency (downward arrow in Fig 5D). Interestingly, the changes became markedly apparent in the GVS condition (downward arrow in Fig 5H). This facilitation started 1 ms after the onset of the excitation that was induced by separate TMS (onset latency: 11.5 ms in both conditions, shown with vertical dotted lines). The mean (± SD) background firing frequency of the MU was 9.71 ± 1.41 Hz. Fig 3I and 3J show the group peak counts in the differential PSTHs with ulnar nerve stimulation at 1.0 × MT obtained from all successfully recorded MUs (n = 31). In 27 of the 31 MUs (87.1%), the facilitatory effects induced by combined stimulation 1 ms after the onset of TMS-induced excitation were larger in the anodal GVS condition than in the control condition (Fig 5I). The firing probabilities of the two conditions differed significantly (d = 0.854, p < 0.01, 1 - β = 0.996, Fig 5J). In contrast, the firing probability within the first 1-ms bins of the TMS-induced peak was not affected by GVS (d = 0.079, p = 0.663, 1 - β = 0.071).


Vestibular stimulation-induced facilitation of cervical premotoneuronal systems in humans
The effects of galvanic vestibular stimulation (GVS) on the firing probability of single motor units (MUs) after combined motor cortex and ulnar nerve stimulation.A–H show the peristimulus time histograms (PSTHs) of a single MU in the biceps brachii (BB) muscle after separate ulnar nerve stimulation (NERVE) at 1.0 × motor threshold (MT) of the first dorsal interosseous muscle (A, E), separate transcranial magnetic stimulation (TMS) (B, F) over the contralateral primary motor cortex at 1.25 × active motor threshold of the BB, and combined stimulation (COMB) (C, G) in the control (A–D) and anodal GVS conditions (E–H). Each PSTH was obtained after 50 stimuli. The counts in these PSTHs were subtracted by the mean counts during a 50 ms prestimulus period. D and H show differential PSTHs after subtraction of the summed PSTHs after separate stimuli from the PSTHs of the COMB. The number of counts in each bin was normalized by the number of triggers. The vertical dashed line represents the onset of the excitatory peak in the PSTH after separate TMS. The superimposed waveforms in the upper right corner of each PSTH show the MU action potentials (n = 50) obtained from each stimulus trial. I–L indicate the peak counts of the MU firings in the differential PSTHs in the control and anodal GVS conditions obtained from 31 MUs that were investigated with the NERVE set at 1.0 × MT (I, J) and 20 MUs that were investigated with the NERVE set at 0.75 × MT (K, L). The error bars represent 1 standard deviation. The analysis window was set at a predefined period (1.0 ms duration) that started 1.0 ms after the onset of the TMS-induced excitatory peak in the PSTH. **p < 0.01.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0175131.g005: The effects of galvanic vestibular stimulation (GVS) on the firing probability of single motor units (MUs) after combined motor cortex and ulnar nerve stimulation.A–H show the peristimulus time histograms (PSTHs) of a single MU in the biceps brachii (BB) muscle after separate ulnar nerve stimulation (NERVE) at 1.0 × motor threshold (MT) of the first dorsal interosseous muscle (A, E), separate transcranial magnetic stimulation (TMS) (B, F) over the contralateral primary motor cortex at 1.25 × active motor threshold of the BB, and combined stimulation (COMB) (C, G) in the control (A–D) and anodal GVS conditions (E–H). Each PSTH was obtained after 50 stimuli. The counts in these PSTHs were subtracted by the mean counts during a 50 ms prestimulus period. D and H show differential PSTHs after subtraction of the summed PSTHs after separate stimuli from the PSTHs of the COMB. The number of counts in each bin was normalized by the number of triggers. The vertical dashed line represents the onset of the excitatory peak in the PSTH after separate TMS. The superimposed waveforms in the upper right corner of each PSTH show the MU action potentials (n = 50) obtained from each stimulus trial. I–L indicate the peak counts of the MU firings in the differential PSTHs in the control and anodal GVS conditions obtained from 31 MUs that were investigated with the NERVE set at 1.0 × MT (I, J) and 20 MUs that were investigated with the NERVE set at 0.75 × MT (K, L). The error bars represent 1 standard deviation. The analysis window was set at a predefined period (1.0 ms duration) that started 1.0 ms after the onset of the TMS-induced excitatory peak in the PSTH. **p < 0.01.
Mentions: Fig 5A–5H illustrate the PSTHs of a single MU in the control and anodal GVS conditions. In the control condition, combined TMS (1.25 × AMT) and ulnar nerve stimulation (1.0 × MT) produced a slight increase in firing probability at a short latency (downward arrow in Fig 5D). Interestingly, the changes became markedly apparent in the GVS condition (downward arrow in Fig 5H). This facilitation started 1 ms after the onset of the excitation that was induced by separate TMS (onset latency: 11.5 ms in both conditions, shown with vertical dotted lines). The mean (± SD) background firing frequency of the MU was 9.71 ± 1.41 Hz. Fig 3I and 3J show the group peak counts in the differential PSTHs with ulnar nerve stimulation at 1.0 × MT obtained from all successfully recorded MUs (n = 31). In 27 of the 31 MUs (87.1%), the facilitatory effects induced by combined stimulation 1 ms after the onset of TMS-induced excitation were larger in the anodal GVS condition than in the control condition (Fig 5I). The firing probabilities of the two conditions differed significantly (d = 0.854, p < 0.01, 1 - β = 0.996, Fig 5J). In contrast, the firing probability within the first 1-ms bins of the TMS-induced peak was not affected by GVS (d = 0.079, p = 0.663, 1 - β = 0.071).

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 &lt; 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.


Related in: MedlinePlus