U.S. experts have developed what they claim to be the most biologically-accurate robotic legs yet, which could help them understand how babies learn to walk, and ultimately serve towards an effective spinal-injury treatment. The study was published in the Journal of Neural Engineering, and describes "the development of a bipedal robot that models the neuromuscular architecture of human walking."
The team from the University of Arizona created a version of the message system generating the rhythmic muscle signals that control walking. They were able to replicate the central pattern generator (CPG), a neuronal network in the lumbar region of the spinal cord. That nerve cell network is responsible for generating rhythmic muscle signals. The CPG produces these signals, and then controls them by gathering information from different parts of the body that are involved in walking and responding to the environment. This CPG is what allows people to walk instinctively, without thinking about it.
The simplest form of a CPG is called a half-center, and consists of two neurons that produce a rhythm by firing signals alternatively, and sensors that deliver information (such as when a leg touches a surface) back to the half-center. The team suggests that babies start off with such a simplistic set-up, then develop a more complex walking pattern over time.
"This robot represents a complete physical, or 'neurorobotic' model of the system, demonstrating the usefulness of this type of robotics research for investigating the neuropsychological processes underlying walking in humans and animals," explained the team.
"Interestingly, we were able to produce a walking gait, without balance, which mimicked human walking with only a simple half-centre controlling the hips and a set of reflex responses controlling the lower limb," said Dr. Theresa Klein, who was involved in the study. "This underlying network may also form the core of the CPG and may explain how people with spinal cord injuries can regain walking ability if properly stimulated in the months after the injury."
According to the team of scientists, the half-centre CPG could explain why babies put on a treadmill have been observed to take steps instinctively, even before actually learning to walk. Matt Thornton, gait analyst laboratory manager at the Royal National Orthopaedic Hospital in the UK, said the study was "an interest development," according to BBC News. "Previous robotic models have mimicked human movement: this one goes further and mimics the underlying human control mechanisms driving that movement," Thornton noted. "It may offer a new approach to investigate and understand the link between nervous system control problems and walking pathologies."
According to Thornton, existing systems for analyzing how people walk accurately measure hip, knee, and ankle joint movements in 3-D while subjects walk on a treadmill. Depending on their condition, patients can have different reactions. "At present this type of analysis provides us with detailed information about the joint, bones and muscles," he said. "The robotic model may go one step further in linking these problems to the nervous system, which actually controls the movement."
"The implications for increased understanding of, for example, patients with spinal cord injury are very exciting," concluded Thornton.
