Tetraplegic patient achieves natural walking ability through innovative digital brain-spine bridge

In a Nature publication, scientists have successfully created an extraordinary wireless digital bridge that enabled a tetraplegic patient to regain the ability to walk naturally, even on challenging terrains. Notably, the patient experienced sustained neurological advancements that persisted even after deactivating the bridge.

Moreover, this remarkable brain-spine interface (BSI), which established a dependable connection within minutes, remained consistently stable over the course of a year, even during the patient's independent usage at home.

Background

When neurons in the lumbosacral spinal cord are affected by spinal cord injuries, it hinders the transmission of crucial executive commands from the brain that are required for walking. As a result, individuals experience profound and enduring paralysis.

About this study

As part of the ongoing clinical feasibility study known as Stimulation Movement Overground (STIMO)-BSI, the researchers conducted all the experiments to assess the functionality of the cortical devices prior to implantation.

A single-participant study

The team tested and validated this digital bridge in a 38-year-old male who sustained an incomplete cervical spinal cord injury ten years prior .

In the STIMO clinical trial, a five-month neurorehabilitation program helped him regain the ability to step forward with the aid of a front-wheel walker via targeted epidural electrical stimulation of the spinal cord.

Despite using stimulation at home for nearly three years, his neurological recovery plateaued, thus, he enrolled in STIMO-BSI.

Digital bridge, its neurosurgical implantation, and calibration

In the current study, a fully implanted recording and stimulation system was utilized as part of the Brain-Spine Interface (BSI) called Stimulation Movement Overground (STIMO). This innovative system established a direct connection between cortical activity and the modulation of epidural electrical stimulation programs. Its purpose was to facilitate the activation of lower limb muscles for standing and walking recovery in individuals with paralysis caused by spinal cord injuries.

To optimize the placement of the BSI implants over the spinal cord and brain, pre-operative procedures were planned. Functional and anatomical imaging data were obtained using computerized tomography (CT) and magnetoencephalography (MEG). This helped identify the specific regions of the cerebral cortex that responded strongly to the intention of moving the lower limbs.

The locations of the implants were then uploaded onto a neuronavigation system. The participant was discharged 24 hours after each neurosurgical intervention. A weighted Aksenova/Markov-switching multilinear algorithm was used to calibrate the BSI during the first session after the surgery. The BSI's gating model determined the probability of intention to move a joint, while another multilinear model predicted the scale and directionality of the intended movement.

With the assistance of the BSI, the participant experienced a significant increase in hip flexor muscle activity within five minutes of calibration, resulting in 97% accuracy in generating torque compared to attempts without the BSI. The BSI framework allowed the participant to control seven different states, gradually gaining control over the movement of each joint bilaterally with an average accuracy of 74% and a low decoder latency of 1.1 seconds.

Walking on complex terrains requires precise muscle activation to support bodyweight, propel, and swing the lower limbs. The BSI enabled the participant to climb a steep ramp nearly twice as fast as without the BSI, highlighting its effectiveness. Over the course of 40 neurorehabilitation sessions, including physiotherapy, the participant successfully performed walking, balancing, and single-joint movements with the BSI.

The participant demonstrated improved standing and walking abilities, leading to an increase in WISCI II scores from six to 16 after participating in the STIMO-BSI program. Additionally, the participant showed notable advancements in conventional clinical assessments, such as the six-minute walk test, as evaluated by blinded physiotherapists. The study team conducted a three-year follow-up with the participant to track progress and outcomes.

Conclusions

Although the researchers conducted their validation of this digital bridge on a single individual, they strongly believe that it has the potential to benefit a broad range of individuals with severe paralysis resulting from spinal injuries at different locations. This belief stems from three key observations:

Firstly, the researchers have confirmed that the physiological principles underlying epidural electrical stimulation of the spinal cord apply to all individuals, regardless of whether their injuries are complete or incomplete.

Secondly, they have successfully developed methods to quickly and reliably calibrate the connection, allowing the patient to operate the brain-spinal interface (BSI) independently at home.

Thirdly, the brain decoding framework utilized in this study has demonstrated similar resilience and consistency in two additional tetraplegic patients.

Undoubtedly, the establishment of a digital bridge between the brain and spinal cord represents the initiation of a new era in the field of motor deficit treatments.

Source : Nature