Researchers from the Alberto Santos Dumont Association for Research Support (AASDAP) in Brazil, in collaboration with EPFL, have developed a non-invasive strategy that combines functional electrostimulation and a brain-machine interface to help people with paraplegia walk again. This rehabilitation approach was tested on two patients, who showed an improvement in their motor skills and a partial neurological recovery.
Every year, nearly 500,000 people around the world find themselves living with disability as a result of a traffic accident or other trauma that has damaged their spinal cord. People with severe injuries lose the vast majority of their motor and sensory abilities in their lower limbs. They may also experience secondary conditions resulting from inactivity, such as bedsores and cardiovascular disorders.
In order to improve their daily lives and restore as many motor functions as possible, research teams from the Alberto Santos Dumont Association for Research Support (AASDAP) in Brazil, in collaboration with EPFL, have developed a new, non-invasive system for lower-limb neurorehabilitation.
Patients use their own brain activity to send electrical impulses to 16 muscles in their legs. With the help of a conventional walker and a body weight support system, they learn to walk again, build muscle strength and improve their motor skills. A haptic interface provides vibrotactile feedback on their arms, giving patients information about the position of their limbs in space. This means they can move their legs without having to constantly look at them.
The system was tested on two patients with chronic paraplegia. At the end of the clinical evaluation, both patients were able to move with a considerable degree of autonomy, and one of them displayed a clear motor improvement. Doctors also noticed enhanced cardiovascular capacity and muscle volume. Significant recovery was achieved without resorting to surgical intervention. The results of this study have been published in Scientific Reports .
Electrodes to measure brain activity and stimulate the legs
The patients wore an EEG headset with electrodes to record the brain’s electrical activity and detect movement intention. Eight electrodes were attached to each leg, stimulating the muscles involved in the walking process. After preliminary training, patients used their own brain activity to send electric impulses to the muscles in either leg.
"We decoded the patients’ motor imagery using a non-invasive brain-machine interface," says Solaiman Shokur, from the AASDAP. "The patients were instructed to imagine moving their left and right legs in turn, and our system used these signals to move the corresponding limb."
With the help of a walker and supported by a harness that bore 60-70% of their body weight, the patients learned to walk again and increased their sensorimotor skills.
This approach, using a predefined walking trajectory, imposes a physiological gait on the patient. The trajectory is associated with a predefined electrostimulation pattern for the lower-limb muscles involved in walking.
"We controlled the electrostimulation through a closed loop. This allowed us to adjust the electrical current applied to the muscles in real time in order to correct for differences between the measured and target hip and knee angles," says Mohamed Bouri, who heads up the Rehabilitation and Assistive Robotics research group, which developed the electrostimulation and the vibrotactile feedback technologies. "That means we can improve muscle activation and reduce muscle fatigue."
Another major component of this approach was the use of a wearable haptic display to deliver tactile feedback to the patients’ forearms in order to provide them with a continuous source of proprioceptive feedback related to their walking. Tactile feedback improves the fluidity of movement and increases patients’ confidence in their ability to walk.
Waking up residual nerves that have been dormant for years
The researchers’ approach is innovative: it is multimodal and doesn’t require invasive surgery. Patients simply need to train on simulators and become familiar with the interface. The results are surprising in that they demonstrate both muscular improvement and progress in neurological functions. "Our hypothesis is that, after a spinal injury, some spinal cord fibers may have survived, but they may not have been activated for years," says Solaiman Shokur. "Our system makes it possible to stimulate them again."
"There is no silver bullet to treat spinal cord injuries," says Miguel Nicolelis, from the AASDAP. "More and more, it looks like we need to implement multiple techniques simultaneously to achieve the best neurorehabilitation results."
This project is the result of a collaboration between the Neurorehabilitation Laboratory of the Alberto Santos Dumont Association for Research Support (AASDAP) , the headquarters of the Walk Again Project , the Biomechanics and Motor Control Laboratory at the Federal University of ABC (UFABC, Santo André, Brazil), and EPFL’s REHAssist research group.