Spinal cord injuries devastate mobility not only by severing motor control, but also by cutting off sensory feedback from the limbs. Without knowing where their legs are in space, individuals struggle to coordinate movement.

Researchers from Brown, Rhode Island Hospital, and VA Providence Healthcare successfully demonstrated two-way communication across complete spinal cord injury sites in three participants paralyzed from the waist down. They published their findings in Nature Biomedical Engineering.

“This is the first time that simultaneous motor stimulation and sensory feedback have been demonstrated in people with complete spinal cord injuries,” says senior author David Borton PhD’12, an associate professor of engineering, of neurosurgery, and of brain science. “By providing both motor activation and simultaneous sensory feedback, we are making progress toward restoring coordinated movements and functional independence.”

The two-week, in-hospital study used electrode arrays implanted both above and below the injury site along the spinal cord. Both arrays delivered patterned electrical stimulation to the spinal cord that can mimic the natural electrical pulses that travel through a healthy spinal cord. Electrical stimulation below the spinal lesion partially restored lower-extremity muscle algorithms with stimulation above the injury site—where neural connections to the brain remain intact—the system translated leg positions into sensations on intact body parts, such as the chest, back, or arms.

During blindfolded testing, physical therapists moved participants’ legs into varying positions. Participants accurately identified their knee angles based solely on the intensity and location of these upper-body sensations.

The ultimate test combined both systems at once. Suspended in a harness above a treadmill, participants engaged the necessary leg muscles for walking while simultaneously receiving real-time feedback on foot placement. Participants correctly engaged walking muscles and accurately identified ground contact. One participant said they “could tell when [my foot] hit based on feedback up to here [pointing to their chest]... it was close.”

While this short-term trial focused on feasibility, researchers believe synchronized motor and sensory stimulation could significantly enhance physical therapy outcomes.

“There’s reason to believe that coordinated stimulation across an injury site could produce positive rehabilitation effects,” Borton says. The team plans to explore long-term therapeutic applications in future studies.