Abstract
Design
Prospective cohort study.
Objectives
We aim to better understand the silent period (SP), an inhibitory counterpart to the well-known motor evoked potential (MEP) elicited by transcranial magnetic stimulation (TMS), in individuals with spinal cord injury (SCI).
Setting
Veterans Affairs Hospital in New York.
Methods
EMG responses were measured in the target abductor pollicis brevis at rest (TMS at 120% of resting motor threshold (RMT)) and during maximal effort (TMS at 110% of RMT). Participants with chronic cervical SCI (n = 9) and AB participants (n = 12) underwent between 3 and 7 sessions of testing on separate days. The primary outcomes were the magnitude and reliability of SP duration, resting and active MEP amplitudes, and RMT.
Results
SCI participants showed significantly lower MEP amplitudes compared to AB participants. SCI SP duration was not significantly different from AB SP duration. SP duration demonstrated reduced intra-participant variability within and across sessions compared with MEP amplitudes. SCI participants also demonstrated a higher prevalence of SP ‘interruptions’ compared to AB participants.
Conclusions
In a small group of individuals with chronic cervical SCI, we confirmed the well-known findings that SCI individuals have lower TMS evoked potential amplitudes and a tendency toward higher TMS motor thresholds relative to able-bodied controls. We did not observe a significant difference in SP duration between individuals with versus without SCI. However, SP duration is a more reliable outcome within and across multiple sessions than MEP amplitude.
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Data availability
Individual-level data are included as Supplementary Data 1 (by participant, averaged across sessions) and Supplementary Data 2 (by participant per session). The LabVIEW code for analyzing SP duration is deposited at https://github.com/neurorehabva/CSP_LabVIEW.
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Funding
The study is funded by the New York State Department of Health C30599 and Craig H. Neilsen Foundation 457648.
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HJS and JRW: Data acquisition; data interpretation; manuscript drafting and revision. OAA: Data interpretation; manuscript revision. YKW: Data acquisition; data interpretation; manuscript revision. NYH: Study conception and design; data interpretation; manuscript drafting and revision.
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The authors declare no competing interests.
Statement of ethics
All procedures were approved by the Institutional Review Board of the James J. Peters VA Medical Center, Bronx, NY (HAR-15-001). We certify that all applicable institutional and governmental regulations concerning the ethical participation of human participants were followed during the course of this research.
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Sfreddo, H.J., Wecht, J.R., Alsalman, O.A. et al. Duration and reliability of the silent period in individuals with spinal cord injury. Spinal Cord 59, 885–893 (2021). https://doi.org/10.1038/s41393-021-00649-x
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DOI: https://doi.org/10.1038/s41393-021-00649-x
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