Question

With respect to talking about brain-spine interface technology, where can the technology or science ultimately go? Include a discussion of the influence of nanoscience or nanotechnology in your response. Carry this topic to its logical/ultimate conclusion. Include in your discussion side effects of this development on a few related technologies and/or sciences.

Answer 1

Walking is made possible by a complex interplay among neurons in the brain and spinal cord. Electrical signals originating in the brain’s motor cortex travel down to the lumbar region in the lower spinal cord, where they activate motor neurons that coordinate the movement of muscles responsible for extending and flexing the leg.

Injury to the upper spine can cut off communication between the brain and lower spinal cord. Both the motor cortex and the spinal neurons may be fully functional, but they are unable to coordinate their activity. The goal of the study was to re-establish some of that communication.

The brain-spinal interface used a pill-sized electrode array implanted in the brain to record signals from the motor cortex. The sensor technology was developed in part for investigational use in humans by the BrainGate collaboration, a research team that includes Brown, Case Western Reserve University, Massachusetts General Hospital, the Providence VA Medical Center, and Stanford University. The technology is being used in ongoing pilot clinical trials, and was used previously in a study led by Brown neuroengineer Leigh Hochberg in which people with tetraplegia were able to operate a robotic arm simply by thinking about the movement of their own hand.

A wireless neurosensor, developed in the neuroengineering lab of Brown professor Arto Nurmikko by a team that included Borton, sends the signals gathered by the brain chip wirelessly to a computer that decodes them and sends them wirelessly back to an electrical spinal stimulator implanted in the lumbar spine, below the area of injury. That electrical stimulation, delivered in patterns coordinated by the decoded brain, signals to the spinal nerves that control locomotion.

To calibrate the decoding of brain signals, the researchers implanted the brain sensor and wireless transmitter in healthy macaques. The signals relayed by the sensor could then be mapped onto the animals’ leg movements. They showed that the decoder was able to accurately predict the brain states associated with extension and flexion of leg muscles.

The ability to transmit brain signals wirelessly was critical to this work, Borton said. Wired brain-sensing systems limit freedom of movement, which in turn limits the information researchers are able to gather about locomotion.

“Doing this wirelessly enables us to map the neural activity in normal contexts and during natural behavior,” Borton said. “If we truly aim for neuroprosthetics that can someday be deployed to help human patients during activities of daily life, such untethered recording technologies will be critical.”

The researchers combined their understanding of how brain signals influence locomotion with spinal maps, developed by Courtine’s lab at EPFL, which identified the neural hotspots in the spine responsible for locomotor control. That enabled the team to identify the neural circuits that should be stimulated by the spinal implant.

With these pieces in place, the researchers then tested the entire system on two macaques with lesions that spanned half the spinal cord in their thoracic spine. Macaques with this type of injury generally regain functional control of the affected leg over a period of a month or so, the researchers said. The team tested their system in the weeks following the injury, when there was still no volitional control over the affected leg.

The study showed that with the system turned on, the animals began spontaneously moving their legs while walking on a treadmill. Kinematic comparisons with healthy controls showed that the lesioned macaques, with the aid of brain-controlled stimulation, were able to produce nearly normal locomotor patterns.

Limitations

While demonstrating that the system works in a nonhuman primate is an important step, the researchers stressed that much more work must be done to begin testing the system in humans. They also pointed out several limitations in the study.

For instance, while the system used in this study successfully relayed signals from the brain to the spine, it lacks the ability to return sensory information to the brain. The team was also unable to test how much pressure the animals were able to apply to the affected leg. While it was clear that the limb was bearing some weight, it wasn’t clear from this work how much.