Abstract

Conventional therapies for spinal cord injury, such as rehabilitation and epidural electrical stimulation, have had limited success in restoring true voluntary walking. Brain-spine interfaces offer a promising solution, enabling voluntary control of movement by linking cortical signals from the sensorimotor cortex to targeted spinal cord stimulation. This article examines how they work, their clinical outcomes in a patient with chronic spinal cord injury and their broader applications in neurological movement disorders.

Introduction

In 2011, Gert-Jan Oskam suffered a cycling accident in China which left him with paralysed legs and partially paralysed arms due to an incomplete cervical spinal cord injury. As a result, he was forced to use a wheelchair for over a decade despite extensive rehabilitation. Twelve years later, in a clinical trial at Lausanne University Hospital, he stood, walked and climbed stairs independently with his own legs. This was driven by his own thoughts via a wireless device that connected his brain and spinal cord. Brain-spine interfaces are a significant development in medical technology, offering a new approach to restoring voluntary movement in paralysed patients.

The Difficulty of Treating Spinal Cord Injuries

Spinal cord injuries do not simply destroy the nervous system. In the majority of cases, the neurons responsible for walking which are located in the lower spinal cord, survive and are intact. Therefore, the problem is that the pathways carrying signals coordinating movement from the sensorimotor cortex to these neurons are damaged. Several therapies such as physical rehabilitation, drug therapies and electrical stimulation of the spinal cord have been tried and showed promise. However, these approaches are limited by the fact that intention-driven signals from the brain are required to ensure movements are truly under the patient’s control. Stimulation activates the relevant muscles but this does not proceed under the patient’s voluntary control.

Understanding the Breakthrough

The device that gave Oskam his movement back is the result of years of scientific progress from the NeuroRestore research group at EPFL and Lausanne University Hospital in Switzerland.

In 2018, Wagner et al. demonstrated that delivering precisely timed electrical impulses to specific nerve roots of the lower spinal cord could restore voluntary walking in three participants with chronic paralysis within one week of implantation. This approach targeted the specific nerves associated with each phase of walking and matched the patient’s intended movements, making the spinal cord more responsive to the brain’s residual signals. This enabled patients to initiate and control movement instead of being involuntarily controlled by the stimulation. After five months of rehabilitation, two participants were able to walk independently with crutches without the need for stimulation.

The following year, Benabid et al. demonstrated that a patient with tetraplegia could control a four-limb exoskeleton using their brain signals, which were wirelessly recorded by electrodes implanted on the surface of the motor cortex. This showed that brain signals could be read accurately by a fully implanted wireless device over a prolonged period of time, highlighting that brain recording and precise spinal stimulation could be integrated.  

How the Brain-Spine Interface Works

The brain-spine interface consists of two fully implanted systems that communicate wirelessly, with the first recording brain activity and the second delivering stimulation to the spinal cord. Two implants containing 64 electrodes each are placed on the surface of the dura of the brain and detect the electrical signals generated when the patient intends to move. These signals are received and decoded by a processing unit in the form of a headset that uses machine learning to determine the limb, joint and degree of force. During Oskam’s first session, this system was calibrated, with the algorithm predicting his intended hip movements with 97% accuracy after only 2 minutes of training. The second system involves an implanted pulse generator in the abdomen connected to an electrode array located over the lower spinal cord. Intentions of movement signal to this generator, which delivers targeted electrical stimulation to the specific nerves responsible for movement within 100 milliseconds. This results in a continuous link between the brain and spinal cord below the injury, enabling seamless voluntary movement.

The Unexpected Result

The primary aim of the trial was to restore voluntary movement with the device’s assistance, but a more significant result came to light during rehabilitation. After months of using the brain-spine interface, Oskam regained the ability to walk with crutches even without use of the device. Over time, his lower limb strength, ability to feel sensation and walking ability improved significantly.

This result was unexpected as Oskam had undergone a rehabilitation programme using spinal cord stimulation over five months. However, his progress had plateaued for three years despite continued use of electrical stimulation. The introduction of the brain-spine interface technology restored the direct link between his intentions and spinal cord. This is thought to have induced neuroplastic changes through the reorganisation of residual neuronal pathways, facilitating further recovery that stimulation alone was unable to achieve.

Wider Implications, Limitations and Future Directions

The brain-spine interface that helped Oskam is one of many fully implanted neural technologies now demonstrating clinical success. However, there are significant limitations which should be acknowledged. For example, the trial only included a single participant with an incomplete spinal cord injury, meaning that the transferability to complete injuries is unknown. The current system also requires a wearable headset and processing unit, with miniaturisation of hardware and larger clinical trials being necessary before widespread use of this technology. Despite these limitations, the trial demonstrates the potential of a fully implanted brain-spine interface to enable voluntary walking after spinal cord injuries and facilitate greater recovery compared to stimulation alone. This technology may also have potential applications beyond spinal cord injury including restoration of arm and hand movement in stroke patients as well as broader uses in other neurological conditions affecting voluntary movement. A direct wireless connection between the brain and spinal cord is not science fiction, but a reality for Gert-Jan Oskam.

References

1. Lorach, H., Galvez, A., Spagnolo, V., Martel, F., Karakas, S., Intering, N., Vat, M., Faivre, O., Harte, C., Komi, S. and Ravier, J., 2023. Walking naturally after spinal cord injury using a brain–spine interface. Nature, 618(7963), pp.126-133.
2. Wagner, F.B., Mignardot, J.B., Le Goff-Mignardot, C.G., Demesmaeker, R., Komi, S., Capogrosso, M., Rowald, A., Seáñez, I., Caban, M., Pirondini, E. and Vat, M., 2018. Targeted neurotechnology restores walking in humans with spinal cord injury. Nature, 563(7729), pp.65-71.
3. Benabid, A.L., Costecalde, T., Eliseyev, A., Charvet, G., Verney, A., Karakas, S., Foerster, M., Lambert, A., Morinière, B., Abroug, N. and Schaeffer, M.C., 2019. An exoskeleton controlled by an epidural wireless brain–machine interface in a tetraplegic patient: a proof-of-concept demonstration. The Lancet Neurology, 18(12), pp.1112-1122.