Researchers from the University of California, Irvine, along with colleagues at Caltech and USC’s Keck School of Medicine, announced on Apr. 16 that they have developed a bidirectional brain-computer interface (BDBCI) enabling a person to control a robotic walking exoskeleton using brain signals while receiving artificial leg sensation through direct electrical stimulation of the sensory cortex.
The development is significant because it addresses both movement and sensory challenges faced by people living with spinal cord injuries or paraplegia. The new system aims to restore more natural walking ability for individuals who have lost lower-extremity motor and sensory function, which can lead to increased health risks and dependence on wheelchairs.
“Millions of people worldwide suffer from paralysis from spinal cord injury, with loss of lower-extremity motor and sensory function leading to wheelchair dependence and increased risk of serious secondary conditions including heart disease, osteoporosis and pressure ulcers,” said Dr. An Do, UC Irvine associate professor of neurology. “Recovering the ability to walk ranks among the highest rehabilitation priorities for paralyzed individuals.” Do said that current robotic gait exoskeletons do not provide users with natural step sensation or intuitive control—limitations this BDBCI seeks to overcome.
The research team reported that their apparatus decodes motor intent from electrocorticography signals recorded in the leg motor cortex while delivering targeted electrical stimulation for artificial sensation. This creates what they describe as a closed-loop experience: “This work demonstrates that it’s feasible to restore both the motor and sensory dimensions of walking using a single, compact, embedded brain-computer interface system,” Do said. He added that this lays groundwork for future fully implantable systems.
In testing involving a 50-year-old woman undergoing epilepsy evaluation surgery—with bilateral interhemispheric subdural electrodes—the participant controlled an exoskeleton over ten exercises. She achieved high performance levels quickly; during blind step-counting tasks she identified steps correctly nearly 93 percent of the time. In further tests distinguishing between right leg, left leg or no stimulation sensations she reached up to 100 percent accuracy in some cases without any adverse events noted.
A key innovation was accessing both leg motor and sensory cortices via bilateral interhemispheric electrocorticography implants along the medial wall between hemispheres—a method described as safe by Dr. Charles Liu from USC Neurorestoration Center: “Although interhemispheric ECoG implantation is more complex than other conventional approaches…it can be performed safely and yields superior results.” Artificial sensation was provided through direct cortical electrical stimulation—a technique researchers say is safest for ambulatory settings—and long-term use has been demonstrated as safe in existing FDA-approved devices.
The portable BDBCI system runs on three microcontrollers handling neural signal acquisition, real-time decoding, electrical stimulation, and wireless communications without needing tethered computers. Lead author Jeffrey Lim called portability essential: “We hope that our system can serve as a prototypical example for such technologies henceforth.” The study used an FDA-approved Ekso GT powered exoskeleton; according to Payam Heydari (UC Irvine), future versions could be fully implantable without transdermal components.
Looking ahead, Zoran Nenadic (UC Irvine) said improvements in decoding algorithms could enable even more robust operation: “Our ultimate goal is to test…on people with complete leg paralysis.” Richard Andersen (Caltech) commented on broader implications: “This study…represents an important proof of concept for a bidirectional interface for walking…providing somatosensory feedback to the legs while a paralyzed participant brain-controlled a robotic gait exoskeleton.”
The project included contributors from UC Irvine’s Department of Biomedical Engineering; Caltech; Keck School at USC; Rancho Los Amigos National Rehabilitation Center; was approved by institutional review boards at UC Irvine and Rancho Los Amigos National Rehabilitation Center; funded by the National Science Foundation.
