You may have heard about an exciting scientific demonstration that kicked off the recent World Cup. Although it didn’t reach most televised coverage of the soccer event, the presentation was a landmark in brain-controlled robotics. The new technology would allow a paralyzed person to use their mind and command a robotic suit to kick a soccer ball. After seeing such futuristic science fiction-esque technology, some of us start to let our minds run wild with visions of standing alongside Tom Cruise and Emily Blunt while kicking alien butt in a robotic exoskeleton. However, there may be a more practical and elegant way to help people with nerve damage.
A recently published article in Science showed the use of light to activate motor neurons, allowing a previously paralyzed leg to move. In the study, researchers developed mouse stem cells that produce a light-sensitive protein. The cells matured for several days and became motor neurons, after which the scientists implanted them into the damaged nerve of a mouse’s paralyzed leg. Next, the researchers let these new cells grow and make connections with the muscles, then used an LED to stimulate the neurons, which, in turn, contracted the leg muscles.
Scientists previously used electrical stimulation to move muscles, but this method is not precise and can produce uncomfortable results. This light stimulation was much more specific and exclusively activated the new motor neurons. How exactly does this work? Neurons have proteins called ion channels that open and close, allowing ions to flow in and out of the cell. Light activates these neurons through specialized ion channels called channelrhodopsins. When channelrhodopsins absorb a specific wavelength of light, the light produces a change in the structure of the ion channels, forcing them to open. This lets positively charged ions, such as calcium, hydrogen, sodium, and potassium, enter the neuron and activate it, allowing it to signal the muscle to move.
Muscle paralysis, which can occur from illness or injury, can result from damage to the motor neurons that would normally relay signals from the brain to the muscle. Implantation of the channelrhodopsin motor neurons bypasses the need for the brain through external control of a fiber optic device. The scientists intend to first use this technique in an important muscle called the diaphragm, which contracts and allows air to enter the lungs. Dr. Barney Bryson of University College London, the primary researcher in this study, says that their “more immediate goal is to target the relatively simple, rhythmic function of the diaphragm muscle in order to enable artificial control of breathing.”
One particular illness that the researchers see as a promising application of this method is amyotrophic lateral sclerosis (ALS), which is a neurodegenerative disease. Patients with ALS often have difficulty breathing, due to damage to the nerve that controls the diaphragm muscle. Because the movement of the diaphragm is relatively uncomplicated but vital, it is an ideal target to move this technique into clinical studies. Adds Dr. Bryson, “The rhythmic contraction of the diaphragm should make it relatively easy to control muscle activity.”
Although this study is mostly a proof-of-principle, it is exciting because of the ability to control specific nerves, restoring function to previously paralyzed muscles. It is tempting to think about the possible applications of this method, but Dr. Bryson warns that this might be premature. “One quite important point to make, however, is that we do not think that this technique will enable paralyzed people to walk – at least not any time soon. It is likely to be between 5-10 years before we can even begin trials in ALS patients to control breathing and any more complex motor functions will depend on advancements in the technology required to control the transplanted cells,” he said. Additionally, scientists will need to develop these same motor neurons from human stem cells, instead of mouse, and the practicality of this method depends on the advancement of an implantable fiber optic cable. Once these obstacles are overcome, it may be possible to use this promising technology to restore finer motor function. For people suffering from paralysis, this could change the nature of treatment and greatly improve their quality of life.
Written by: Amanda Chung