Standing Neurophysiological Assessment of Lower Extremity Muscles Post-Stroke

Summary

This protocol describes the process for performing a neurophysiological assessment of the lower extremity muscles, tibialis anterior and soleus, in a standing position using TMS in people post-stroke. This position provides a greater probability of eliciting a post-stroke TMS response and allows for the use of reduced stimulator power during neurophysiological assessments.

Abstract

Transcranial magnetic stimulation (TMS) is a common tool used to measure the behavior of motor circuits in healthy and neurologically impaired populations. TMS is used extensively to study motor control and the response to neurorehabilitation of the upper extremities. However, TMS has been less utilized in the study of lower extremity postural and walking-specific motor control. The limited use and the additional methodological challenges of lower extremity TMS assessments have contributed to the lack of consistency in lower extremity TMS procedures within the literature. Inspired by the decreased ability to record lower extremity TMS motor evoked potentials (MEP), this methodological report details steps to enable post-stroke TMS assessments in a standing posture. The standing posture allows for the activation of the neuromuscular system, reflecting a state more akin to the system's state during postural and walking tasks. Using dual-top force plates, we instructed participants to equally distribute their weight between their paretic and non-paretic legs. Visual feedback of the participants' weight distribution was provided. Using image guidance software, we delivered single TMS pulses via a double-cone coil to the participants' lesioned and non-lesioned hemispheres and measured the corticomotor response of the paretic and non-paretic tibialis anterior and soleus muscles. Performing assessments in the standing position increased the TMS response rate and allowed for the use of the lower stimulation intensities compared to the standard sitting/resting position. Utilization of this TMS protocol can provide a common approach to assess the lower extremity corticomotor response post-stroke when the neurorehabilitation of postural and gait impairments are of interest.

Introduction

Transcranial magnetic stimulation (TMS) is an instrument used to measure the behavior of neural circuits. The majority of TMS investigations focusing on the study of motor control/performance have been conducted in the upper extremities. The imbalance between the upper and lower extremity studies is in part due to the additional challenges in measuring the lower extremity corticomotor response (CMR). Some of these methodological obstacles include the smaller cortical representations of the lower extremity muscles within the motor cortex and the deeper location of the representations relative to the scalp¹. In populations with neurological injur....

Protocol

All procedures were approved by the Institutional Review Board at the Medical University of South Carolina and conformed to the Declaration of Helsinki.

1. Participant recruitment

1. Recruit individuals post-stroke from the local database. For this experiment, 16 individuals were recruited from a local electronic recruitment database. In some instances, participants were recruited specifically because they had failed to respond to TMS at rest in previous studies performed by our resea.......

Discussion

The experimental protocol was well tolerated by most participants. One individual was unable to complete the standing TMS evaluation due to preexisting decubitus ulcers secondary to diabetic complications and orthopedic issues involving preexisting knee pain. The amount of loading/unloading of body weight from the legs was minimal. However, there was, on average, a slightly greater downward force measured during the application of the TMS pulses. This is likely due to the weight of the coil and the downward pressure appl.......

Materials

Name	Company	Catalog Number	Comments
Data Acquisition Software	MathWorks	MatLab	The custom data collection program was written in Matlab. However, other software/hardware providers can be used (e.g. National Instruments, AD Instruments, CED Spike2 or Signal)
Double-cone coil	Magstim	D110	Double-cone coil for TMS pulse delivery
Dual force plate	Advanced Mechanical Technology Inc (AMTI)	Dual-top Accusway	Force plate used to measure force/weight distrobution under each leg independently.
Dual-pulse TMS	Magstim	Bistim 200	Connects two Magstim 200 units together for dual-pulse applications
EMG pre-amplifiers	Motion Labs Inc	MA-422	Preamplifiers for disposable surface EMG electrodes
EMG system	Motion Labs Inc	MA400	EMG system for data collection
Neuronavigation System	Rogue Research	Brainsight	Software and hardware used to ensure consistent placement/delivery of magnetic stimulations. Marking the stimulation location on a participant's head or on a place showercap can also be used in the absence of neuronavigational software.
Recruitment Database	N/A	N/A	Electronic database including names of possible individuals who are eligble for your studies.
TMS unit (x2)	Magstim	Magstim 200	Delivers TMS pulses