Collinger and Colleagues Publish Research Sensing and Decoding the Neural Drive to Paralyzed Muscles

January 8, 2022

Jennifer Collinger, PhD, associate professor, UPMC Department of Physical Medicine and Rehabilitation – along with colleagues from universities across the US, UK, and Germany – published research evaluating the feasibility of deriving motor control signals from a wearable sensor that can detect residual motor unit activity in paralyzed muscles after chronic cervical spinal cord injury (SCI).

Motor neurons convey information about motor intent that can be extracted and interpreted to control assistive devices. However, most methods for measuring the firing activity of single neurons rely on implanted microelectrodes. Although intracortical brain-computer interfaces (BCIs) have been shown to be safe and effective, the requirement for surgery poses a barrier to widespread use that can be mitigated by instead using noninvasive interfaces.

The objective of this study was to evaluate the feasibility of deriving motor control signals from a wearable sensor that can detect residual motor unit activity in paralyzed muscles after chronic cervical spinal cord injury (SCI). Despite generating no observable hand movement, volitional recruitment of motor units below the level of injury was observed across attempted movements of individual fingers and overt wrist and elbow movements.

Subgroups of motor units were coactive during flexion or extension phases of the task. Single digit movement intentions were classified offline from the electromyogram (EMG) power [root-mean-square (RMS)] or motor unit firing rates with median classification accuracies >75% in both cases. Simulated online control of a virtual hand was performed with a binary classifier to test feasibility of real-time extraction and decoding of motor units. The online decomposition algorithm extracted motor units in 1.2 ms, and the firing rates predicted the correct digit motion 88 ± 24% of the time.

A wearable electrode array and machine learning methods were used to record and decode myoelectric signals and motor unit firing in paralyzed muscles of a person with motor complete tetraplegia. The myoelectric activity and motor unit firing rates were task specific, even in the absence of visible motion, enabling accurate classification of attempted single-digit movements. This wearable system has the potential to enable people with tetraplegia to control assistive devices through movement intent.

This study provides the first demonstration of a wearable interface for recording and decoding firing rates of motor units below the level of injury in a person with motor complete.

Learn more here.

Other Study Contributors

Jordyn Ting
Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania

Alessandro Del Vecchio
Department of Artificial Intelligence in Biomedical Engineering, Friedrich-Alexander University Erlangen-Nürnberg, Erlangen, Germany

Devapratim Sarma
Center for the Neural Basis of Cognition, Carnegie Mellon University and University of Pittsburgh, Pittsburgh, Pennsylvania

Nikhil Verma
Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania

Samuel Colachis, IV
Medical Devices and Neuromodulation Group, Battelle Memorial Institute, Columbus, Ohio

Nicholas Annetta
Medical Devices and Neuromodulation Group, Battelle Memorial Institute, Columbus, Ohio

Dario Farina
Department of Bioengineering, Imperial College London, London, United Kingdom

Douglas Weber
Neuroscience Institute, Carnegie Mellon University, Pittsburgh, Pennsylvania