UC Irvine researchers (from left) Dr. An Do, associate professor of neurology; Payam Heydari, professor of electrical engineering and computer science; and Zoran Nenadic, professor of biomedical engineering, recently participated in a study that demonstrated a brain-computer interface technology that enables spinal cord injury patients to walk with a robotic exoskeleton and feel lifelike sensory responses, a key factor in safe and realistic mobility.
Photo Credit: Debbie Morales / UC Irvine
Scientific Frontline: Extended "At a Glance" Summary: Bidirectional Brain-Computer Interface for Walking
The Core Concept: A bidirectional brain-computer interface (BDBCI) that enables individuals to control a robotic walking exoskeleton using brain signals while simultaneously receiving artificial leg sensation through direct electrical stimulation of the sensory cortex.
Key Distinction/Mechanism: Unlike existing robotic exoskeletons that rely on manual control and lack sensory feedback, this system decodes motor intent from electrocorticography (ECoG) signals in the leg motor cortex and delivers real-time artificial sensation to the somatosensory cortex. This bidirectional approach creates a closed-loop, brain-driven walking experience, which improves gait speed and reduces the risk of falls.
Major Frameworks/Components:
- Bidirectional Brain-Computer Interface (BDBCI): An embedded, portable platform utilizing high-speed microcontrollers for neural signal acquisition, real-time decoding, electrical stimulation, and wireless communication without relying on a tethered computer.
- Bilateral Interhemispheric Electrocorticography (ECoG): Implants strategically placed to access the leg motor and sensory cortices within the medial wall of the brain along the interhemispheric fissure.
- Direct Cortical Electrical Stimulation: A localized technique used to safely and practically elicit artificial sensory feedback directly in the somatosensory cortex.
- Robotic Gait Exoskeleton: Integration with a powered exoskeleton to translate decoded brain signals into physical, bilateral lower-extremity movement.
Branch of Science: Biomedical Engineering, Neurology, Neuroscience, Electrical Engineering, and Computer Science.
Future Application: The technology establishes the foundation for fully implantable, miniaturized BDBCI systems. Future iterations aim to eliminate transdermal components using subcutaneous cables and system-on-a-chip integration, reducing infection risks and enabling chronic, everyday use for individuals with complete leg paralysis.
Why It Matters: Millions of people worldwide experience paralysis from spinal cord injuries, leading to wheelchair dependence and serious secondary health conditions. By restoring both the motor and sensory dimensions of mobility, this interface offers a critical pathway toward achieving safe, naturalistic, and full ambulatory function for patients with paraplegia.
Researchers at the University of California, Irvine, Caltech and Keck School of Medicine of USC have developed a bidirectional brain-computer interface that allows a person to control a robotic walking exoskeleton using brain signals and receive artificial leg sensation through direct electrical stimulation of the sensory cortex.
The project is the first implementation of a BDBCI for walking that incorporates bilateral interhemispheric leg sensorimotor brain areas and represents a critical step toward restoring full ambulatory function in individuals living with spinal cord injury and paraplegia. The team’s results are reported in a paper published recently in the journal Brain Stimulation.
“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 co-author Dr. An Do, UC Irvine associate professor of neurology. “Recovering the ability to walk ranks among the highest rehabilitation priorities for paralyzed individuals.”
He said that while robotic gait exoskeletons have emerged as a promising technology for restoring walking ability, existing systems rely on manual control and provide no sensory feedback, a significant limitation as impairment of the sensation of taking steps is known to reduce gait speed and increase the risk of falls.
The team’s BDBCI apparatus directly addresses both these challenges. By decoding motor intent from electrocorticography signals recorded from the leg motor cortex and delivering artificial leg sensation through targeted electrical stimulation of the somatosensory cortex, it creates a closed-loop, brain-driven experience of walking.
“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. “We believe this lays a critical foundation for the development of fully implantable systems that could one day give paraplegic patients a meaningful and natural sense of movement.”
The participant in the study was a 50-year-old woman undergoing epilepsy evaluation with bilateral interhemispheric subdural electrocorticography implantation. She operated the BDBCI-controlled exoskeleton across 10 exercises, rapidly achieving a high level of performance, which demonstrated the system’s accessibility and reliability, according to the researchers.
To validate artificial sensory feedback, the subject completed a blind step-counting task, correctly identifying steps with an overall accuracy of almost 93 percent. In an additional sensory discrimination task, she identified right leg, left leg and null (no stimulation) feelings with 96, 84 and 100 percent accuracy, respectively. The participant confirmed in all 10 runs that exoskeleton steps triggered matching contralateral leg sensations and reported that the sensory feedback aided task performance. No adverse events were noted throughout the study, the researchers said.
A key innovation of this project was the use of bilateral interhemispheric electrocorticography implants to access the leg motor and sensory cortices in the medial wall of the brain along the interhemispheric fissure.
“Although interhemispheric ECoG implantation is more complex than other conventional approaches, our team demonstrated that it can be performed safely and yields superior results,” said co-author Dr. Charles Liu, professor of neurological surgery and director of the USC Neurorestoration Center at Keck School of Medicine of USC. “The leg motor cortex in the interhemispheric region provides more robust and reliable neural signal modulation associated with leg movements, making it likely the most optimal recording site for BCI walking applications.”
Artificial sensation was delivered through direct cortical electrical stimulation, a technique the researchers identify as the safest and most practical option for eliciting leg sensation in ambulatory settings. Because ECoG electrode arrays can be implanted to simultaneously cover both the motor cortex for movement decoding and the somatosensory cortex for sensory stimulation, the BDBCI system incurs no additional surgical risk. Long-term cortical electrical stimulation has also been demonstrated as safe in existing commercial devices approved by the U.S. Food and Drug Administration.
The entire BDBCI system was implemented on a compact, portable, embedded platform consisting of three 48-megahertz microcontrollers that jointly perform all system functions – including neural signal acquisition, real-time decoding, electrical stimulation and wireless communications – without reliance on a tethered computing system.
“This type of portability is necessary to be practical for patients’ everyday use. We hope that our system can serve as a prototypical example for such technologies henceforth,” said lead author Jeffrey Lim, UC Irvine postdoctoral scholar in biomedical engineering.
The robotic gait exoskeleton used in the study was the Ekso GT from Ekso Bionics, an FDA-approved powered device. The embedded design positions the BDBCI as a benchtop version of an implantable system; it’s the first of its kind to combine bilateral lower-extremity artificial sensation with motor decoding in a single BDBCI robotic gait exoskeleton.
“We are looking ahead to a fully implantable version of the BDBCI in which a skull-mounted unit connects via a subcutaneous cable to a chest wall-implanted unit housing all signal processing, stimulation and wireless communication electronics,” said co-author Payam Heydari, UC Irvine professor of electrical engineering and computer science. “Such a system would eliminate transdermal components that pose infection risks and enable chronic implantation in paraplegic spinal cord injury patients.”
He added that further miniaturization is possible through advanced multilayer printed circuit boards, smaller surface-mounted components and conventional semiconductor system-on-a-chip integration. Earlier work at UC Irvine achieved significant size reduction and energy efficiency through integrated circuit implementation.
According to co-author Zoran Nenadic, UC Irvine professor of biomedical engineering, further technical advances can be achieved via refinement of motor decoding algorithms and mitigation of electrical stimulation artifacts, enabling future systems to operate more robustly while providing continuous artificial sensation. “Our ultimate goal is to test the function of such a system on people with complete leg paralysis, demonstrating its potential to mimic the function of an intact sensorimotor loop,” he said.
Co-author Richard Andersen, Caltech’s James G. Boswell Professor of Neuroscience, said that his and other laboratories have been working for several years on bidirectional interfaces to restore somatosensations to the hands of tetraplegic subjects so they can manipulate objects with robotic hands.
“This study by UC Irvine’s Jeffrey Lim and colleagues 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,” Andersen said. “Paraplegic subjects using exoskeletons currently lack natural somatosensory feedback and must rely on visual feedback. This research provides a new avenue for more naturalistic and effective use of walking exoskeletons.”
Funding: The project was funded by the National Science Foundation
Published in journal: Brain Stimulation
Title: Real-time brain-computer interface control of walking exoskeleton with bilateral sensory feedback
Authors: Jeffrey Lim, Po T. Wang, Won Joon Sohn, Derrick Lin, Shravan Thaploo, Luke Bashford, David A. Bjanes, Angelica Nguyen, Hui Gong, Michelle Armacost, Susan J. Shaw, Spencer Kellis, Brian Lee, Darrin J. Lee, Payam Heydari, Richard A. Andersen, Zoran Nenadic, Charles Y. Liu, and An H. Do
Source/Credit: University of California, Irvine
Reference Number: bmed041626_01