The worldwide incidence of spinal cord injury (SCI) is between 250,000 and 500,000 annually.1 Following cervical SCI, approximately 20% of individuals have tetraplegia, but the extent of sensorimotor deficit depends on the type of spinal cord lesion.2 The higher and more complete injury to the cervical spinal cord, the more pronounced the paralysis of the arms, wrists and fingers.1 Therapeutic approaches aim to restore mobility and improve quality of life.2 Recently, a man with tetraplegia cortically controlled a robotic exoskeleton and was able to simulate walking.2 The results were published in Lancet Neurology.2
Exoskeletons include hand orthoses, arms and lower limb exoskeletons.2 They are used with electroencephalogram (EEG)-based brain-computer interfaces for rehabilitation or neurological recovery of patients with severe motor impairment caused by stroke or SCI.2 The exoskeleton can be controlled by trigger signals from residual volitional functions or brain electrical activity.2 While cortical activity has been used for the control of exoskeletons since 1998, a clinically compatible solution for motor deficits still does not exist.2
Researchers from the Clinatec research centre, associated with Grenoble University Hospital in Grenoble, France, designed a program to provide tetraplegic patients with an original neuroprosthesis that would be controlled by the patient’s brain.2 The brain-computer interface system included a fully implantable epidural recorder with 64 electrodes bilaterally implanted over the sensorimotor cortex, a wearable motorized exoskeleton with four limbs, embedded decoding algorithms and software.2
Although two patients were enrolled, only one completed the trial.2 After the recorders were implanted into the first patient, they were shortly activated but stopped communicating.2 The recorders were explanted, and the patient was excluded.2 The technical issue with the recorders was then identified and corrected before the second patient’s implantation.2 The second patient was a 28-year-old man with tetraplegia following a C4-C5 SCI.2 He had little motor control of the upper limbs, and movements were possible only by contraction of biceps at the elbow and of extensors of the wrist. All other muscles did not allow execution of any task.2 However, his functional magnetic resonance imaging (fMRI) and magnetoencephalography (MEG) recordings indicated that he had good capacity to produce cortical signals when imagining himself moving all his limbs.2
After implantation of the recorders, the patient mentally triggered on-off events on various effectors, such as a video game to imitate walking, an avatar (to represent the exoskeleton), or when wearing the suspended exoskeleton over 24 months. To achieve a high-dimensional control of the exoskeleton, the number of degrees of freedom was increased gradually from a brain switch to eight degrees of freedom.2 The patient was able to walk using the exoskeleton, reach-and-touch with both hands, and a 3D, two-handed task that required multi-limb activation of the exoskeleton to generate models that simultaneously controlled several degrees of freedom in combined tasks.2 The patient’s dimensionality of control increased progressively from walking tasks to bimanual tasks.2
This study described the first successful long-term use of wireless epidural multi-channel recorders bilaterally implanted in a tetraplegic patient.2 The long-term combination of bilateral electrodes allowed for the exploration of high-dimensional control in multiple limbs, and no signal degradation, side effects, or long-lasting tolerance were observed in the study.2 While this serves as a proof-of-concept demonstration, further technological developments are required to make the system compatible with long-term human use as the exoskeleton used in this study does not allow autonomous walking with equilibrium – an issue that warrants future research in this field.2
1. Mekki M et al. Robotic Rehabilitation and Spinal Cord Injury: a Narrative Review. Neurotherapeutics. 2018;15(3):604-617.
2. Benabid AL et al. An exoskeleton controlled by an epidural wireless brain–machine interface in a tetraplegic patient: a proof-of-concept demonstration. The Lancet Neurology. 2019;0(0).