Abstract
The soleus H-reflex modulation pattern was investigated during stepping following transspinal stimulation over the thoracolumbar region at 15, 30, and 50 Hz with 10 kHz carry-over frequency above and below the paresthesia threshold. The soleus H-reflex was elicited by posterior tibial nerve stimulation with a single 1 ms pulse at an intensity that the M-wave amplitudes ranged from 0 to 15% of the maximal M-wave evoked 80 ms after the test stimulus, and the soleus H-reflex was half the size of the maximal H-reflex evoked on the ascending portion of the recruitment curve. During treadmill walking, the soleus H-reflex was elicited every 2 or 3 steps, and stimuli were randomly dispersed across the step cycle which was divided in 16 equal bins. For each subject and condition, the soleus M-wave and H-reflex were normalized to the maximal M-wave. The soleus background electromyographic (EMG) activity was estimated as the linear envelope for 50 ms duration starting at 100 ms before posterior tibial nerve stimulation for each bin. The gain was determined as the slope of the relationship between the soleus H-reflex and the soleus background EMG activity. The soleus H-reflex phase-dependent amplitude modulation remained unaltered during transspinal stimulation, regardless frequency, or intensity. Similarly, the H-reflex slope and intercept remained the same for all transspinal stimulation conditions tested. Locomotor EMG activity was increased in knee extensor muscles during transspinal stimulation at 30 and 50 Hz throughout the step cycle while no effects were observed in flexor muscles. These findings suggest that transspinal stimulation above and below the paresthesia threshold at 15, 30, and 50 Hz does not block or impair spinal integration of proprioceptive inputs and increases activity of thigh muscles that affect both hip and knee joint movement. Transspinal stimulation may serve as a neurorecovery strategy to augment standing or walking ability in upper motoneuron lesions.
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Change history
15 March 2024
In this article, the family name of the author Abdullah M. Sayed Ahmad was incorrect. This has been corrected.
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Funding
This work was supported by the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) of the National Institutes of Health (NIH) under Grant Number R01HD100544 and by the New York State Department of Health (NYSDOH), Spinal Cord Injury Research Board (SCIRB) under Contracts C35594GG and C38333GG awarded to Maria Knikou. The funding sources were not involved in study design, data collection, data analysis, data interpretation, or decision to publish.
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AMS: performed experiments, analyzed data, and approved the final version of the manuscript.
MR, YA, MM, JF, SKS, AS: performed experiments, and approved the final version of the manuscript.
MK: conception and design of research, performed experiments, analyzed data, prepared figures, interpreted results of experiments, wrote the first draft of the manuscript, approved the final version of the manuscript.
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Sayed Ahmad, A.M., Raphael, M., Han, J.F. et al. Soleus H-reflex amplitude modulation during walking remains physiological during transspinal stimulation in humans. Exp Brain Res (2024). https://doi.org/10.1007/s00221-024-06779-x
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DOI: https://doi.org/10.1007/s00221-024-06779-x