Stimulus Intensity Affects Variability of Motor Evoked Responses of the Non-Paretic, but Not Paretic Tibialis Anterior Muscle in Stroke.

Anjali Sivaramakrishnan,Sangeetha Madhavan

doi:10.3390/brainsci10050297

Anjali Sivaramakrishnan, Sangeetha Madhavan

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https://doi.org/10.3390/brainsci10050297

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Journal: Brain Sciences	Publication Date: May 15, 2020
Citations: 8	License type: CC BY 4.0

Affiliation: University of Illinois at Chicago

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Background: Transcranial magnetic stimulus induced motor evoked potentials (MEPs) are quantified either with a single suprathreshold stimulus or using a stimulus response curve. Here, we explored variability in MEPs influenced by different stimulus intensities for the tibialis anterior muscle in stroke. Methods: MEPs for the paretic and non-paretic tibialis anterior (TA) muscle representations were collected from 26 participants with stroke at seven intensities. Variability of MEP parameters was examined with coefficients of variation (CV). Results: CV for the non-paretic TA MEP amplitude and area was significantly lower at 130% and 140% active motor threshold (AMT). CV for the paretic TA MEP amplitude and area did not vary with intensity. CV of MEP latency decreased with higher intensities for both muscles. CV of the silent period decreased with higher intensity for the non-paretic TA, but was in reverse for the paretic TA. Conclusion: We recommend a stimulus intensity of greater than 130% AMT to reduce variability for the non-paretic TA. The stimulus intensity did not affect the MEP variability of the paretic TA. Variability of MEPs is affected by intensity and side tested (paretic and non-paretic), suggesting careful selection of experimental parameters for testing.

Highlights

Transcranial magnetic stimulation (TMS) induced motor evoked potentials (MEP) are widely used as a neurophysiological biomarker to assess corticomotor excitability of the central nervous system and determine the magnitude of neurophysiological change induced with motor practice or training
We have found that intensities greater than 140% active motor threshold (AMT) with the double cone coil is not well tolerated by participants with stroke
This study provides new information for variability in MEP parameters over different stimulus intensities in participants with stroke

Summary

Introduction

Transcranial magnetic stimulation (TMS) induced motor evoked potentials (MEP) are widely used as a neurophysiological biomarker to assess corticomotor excitability of the central nervous system and determine the magnitude of neurophysiological change induced with motor practice or training. Transcranial magnetic stimulus induced motor evoked potentials (MEPs) are quantified either with a single suprathreshold stimulus or using a stimulus response curve. We explored variability in MEPs influenced by different stimulus intensities for the tibialis anterior muscle in stroke. Methods: MEPs for the paretic and non-paretic tibialis anterior (TA) muscle representations were collected from 26 participants with stroke at seven intensities. Results: CV for the non-paretic TA MEP amplitude and area was significantly lower at 130% and 140% active motor threshold (AMT). The stimulus intensity did not affect the MEP variability of the paretic TA. Variability of MEPs is affected by intensity and side tested (paretic and non-paretic), suggesting careful selection of experimental parameters for testing

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