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Open Access Highly Accessed Research

Forelimb EMG-based trigger to control an electronic spinal bridge to enable hindlimb stepping after a complete spinal cord lesion in rats

Parag Gad1, Jonathan Woodbridge2, Igor Lavrov3, Hui Zhong3, Roland R Roy35, Majid Sarrafzadeh2 and V Reggie Edgerton345*

  • * Corresponding author: V R Edgerton vre@ucla.edu

  • † Equal contributors

Author Affiliations

1 Biomedical Engineering IDP, University of California, Los Angeles, CA, 90095, USA

2 Department of Computer Science, University of California, Los Angeles, CA, 90095, USA

3 Department of Integrative Biology and Physiology, University of California, Los Angeles, CA, 90095, USA

4 Neurobiology, University of California, Los Angeles, CA, 90095, USA

5 Brain Research Institute, University of California, Los Angeles, CA, 90095, USA

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Journal of NeuroEngineering and Rehabilitation 2012, 9:38  doi:10.1186/1743-0003-9-38

Published: 12 June 2012

Abstract

Background

A complete spinal cord transection results in loss of all supraspinal motor control below the level of the injury. The neural circuitry in the lumbosacral spinal cord, however, can generate locomotor patterns in the hindlimbs of rats and cats with the aid of motor training, epidural stimulation and/or administration of monoaminergic agonists. We hypothesized that there are patterns of EMG signals from the forelimbs during quadrupedal locomotion that uniquely represent a signal for the “intent” to step with the hindlimbs. These observations led us to determine whether this type of “indirect” volitional control of stepping can be achieved after a complete spinal cord injury. The objective of this study was to develop an electronic bridge across the lesion of the spinal cord to facilitate hindlimb stepping after a complete mid-thoracic spinal cord injury in adult rats.

Methods

We developed an electronic spinal bridge that can detect specific patterns of EMG activity from the forelimb muscles to initiate electrical-enabling motor control (eEmc) of the lumbosacral spinal cord to enable quadrupedal stepping after a complete spinal cord transection in rats. A moving window detection algorithm was implemented in a small microprocessor to detect biceps brachii EMG activity bilaterally that then was used to initiate and terminate epidural stimulation in the lumbosacral spinal cord. We found dominant frequencies of 180–220 Hz in the EMG of the forelimb muscles during active periods, whereas these frequencies were between 0–10 Hz when the muscles were inactive.

Results and conclusions

Once the algorithm was validated to represent kinematically appropriate quadrupedal stepping, we observed that the algorithm could reliably detect, initiate, and facilitate stepping under different pharmacological conditions and at various treadmill speeds.

Keywords:
Spinal cord injury; Spinal bridge-assisted stepping; EMG detection; Fast Fourier transform