Brain Control of Paralyzed Limb Lets Monkey Walk Again

A schematic of how Swiss scientists established a wireless connection between the brain of a paralyzed monkey and its spinal cord, allowing it to walk.

In a step toward an electronic treatment for paralysis, Swiss scientists say two partly paralyzed monkeys have been able to walk under control of a brain implant.

The studies, carried out at the École Polytechnique Fédérale in Lausanne, Switzerland, successfully created a wireless bridge between the monkeys’ brains and hind limbs, permitting them to advance along a treadmill with a tentative gait.

The research, published today in the journal Nature, brings together several technologies: a brain implant that senses an animal’s intention to walk, electrodes attached to the lower spinal cord that can stimulate walking muscles, and a wireless connection between the two.

“It’s fantastic to show that you can link those together,” says Chad Bouton, head of the Center for Bioelectronic Medicine at the Feinstein Institute for Medical Research in New York. Bouton recently worked with a human volunteer who used brain signals to control his paralyzed hand, by way of a sleeve wired with electrodes, and others have shown patients can gain brain-control over robots.

The new research appears to be the first time wireless brain-control was established to restore walking in an animal. It is part of a campaign by scientists to develop systems that are “fully implantable and invisible” and which could restore volitional movement to paralyzed people, says Bouton.

The experiments were carried out by an international team led by Grégoire Courtine, a neuroscientist who specializes in epidural electrical stimulation, or zapping the lower spinal cord as a way to provoke stepping movements.

Unlike arm movements, walking is an automated motion coӧrdinated by the spinal cord in a partly independent fashion. Courtine’s group previously demonstrated that they could get a paralyzed rat to walk by stimulating its spine. But in that case the researchers were like puppeteers controlling the animal’s hind legs.

In their report, the scientists describe how they took the next step: make an animal’s brain control the walking.

Two rhesus monkeys were given injuries to one side of the spinal cord, which temporarily left one leg paralyzed. Courtine’s team then surgically implanted into their brains a thumbtack-sized array of electrodes, able to record the electrical activity of neurons in an area of the brain that directs leg movements.

Using a wireless transmitter developed at Brown University, and which attaches to the skull, these brain signals were relayed to a special jacket worn by the monkeys. If the monkey was thinking of walking, it trigged a pre-programmed sequence of electrical stimuli to the lower spinal cord. 

Without assistance from the system, one monkey hopped along a treadmill with the injured leg dangling. Once the system was turned on, however, the monkey began lifting and lowering the leg and placing weight on it.

Courtine is founder of an EPFL spin-off company, G-Therapeutics, which has raised about $40 million and is developing the spinal cord stimulation technology, although not yet combining it with brain implants.

With Jocelyne Bloch, a neurosurgeon at the Lausanne University Hospital and company cofounder, it is testing spinal stimulation in eight volunteers as part of a rehabilitation program. Courtine says “one of the next steps” would be to try to give patients direct brain control over such systems an experiment he hopes to carry out within five years.