A backbreaking injury or stroke that severs the connection the brain uses to send signals to the rest of the body can result in paralysis. But now, scientists are developing technology that can read signals directly from the brain and restore motion to a paralyzed hand - no healthy spine required.
And we're not talking about a small twitch: They can make a paralyzed hand grasp something by reading the electrical stimuli put out by the brain and bypassing the spine to deliver those signals directly to the hand.
In a study published yesterday in the journal Frontiers in Neuroscience, researchers showed that temporarily paralyzed monkeys could use brain implants connected to electrodes to tell their hands to grab onto a lever and pull it towards them. Watch:
In the above GIF, you can see when the monkey starts sending the signal to the hand to start pulling the lever when the line under "Flexor Digitorum Profundus" starts to spike.
The Experiment
Researchers demonstrated the process using two healthy Rhesus macaque monkeys. In both they installed electrodes under the skin that would stimulate the muscles in the forearm and hand. They installed implants, or neural prosthetics, in the brains of the monkeys, and surgically tunneled the electrodes up so that there was a direct connection between brain and hand.
Instead of relying on a spine to transmit signals from the brain to the hand, the scientists used this artificial electrode system to bypass damaged areas.
The macaques were trained to pull the lever and hold it in place for a moment before returning it to its position. Such grasping motion is actually quite complex: It requires coordination between the brain and many muscles in the hand and arm. After a success, the monkey would receive a piece or fruit or a drop of yogurt.
During the trials the monkeys were injected with a drug called muscimol (interestingly also the main psychoactive component in some psychedelic mushrooms), which reliably paralyzed one monkey and somewhat less reliably paralyzed the other, though it inhibited hand and arm muscles the most.
Since many spinal injuries and strokes cause paralysis but leave some neural connections intact, researchers say that demonstrating that implants can restore grasping in these cases is important - so even if one monkey wasn't completely paralyzed, the results are still relevant.
The monkey with the less paralyzed response showed that the implants could effectively tell the arm to grasp and pull the lever. The other monkey was successful in some trials but not all, though researchers think that it may have had its electrodes set up in a less effective way.
According to Dr. Andrew Jackson of Newcastle University, who led the research, this is the first time that it's been shown that the connection between the brain and the nerves and muscles that control grasping can be artificially restored.
Restoring Paralysis In Humans
Restoring the ability to grasp is new, but researchers have been experimenting with stimulating the spinal cord to restore movement for some time.
Prior studies have shown that direct stimulation can make arms and legs move. The eventual goal is to use the results of this study to try and create an implant that would allow the brain to send signals to electrodes that could then activate neural networks and move body parts, as demonstrated with monkeys here.
The same researchers who conducted this study have shown that they can read the human brain sending the same movement signals to the hand, which can then be interpreted by moving a ball on a screen, as demonstrated in the GIF below.
Still, there are some obstacles. After 100 days, some scarring was seen around the electrodes in one monkey, which could cause problems in someone who would have long-term implants.
Additionally, when a person breaks their back and injures their spinal cord, the parts of their brain that control motion change over time, which could present complications that differ from these monkey test subjects. However, the researchers who conducted this study say that it's still possible to read the electrical signals that would control motion in the brain of a person who has been paralyzed for an extended period of time.
Over a long period of time, researchers speculate, continued stimulation in this way would strengthen neural networks, perhaps helping restore the connection between brain and body. The neural connections that remain, especially in the case of a stroke or partial paralysis, might actually get stronger over time. And they think it won't take long to develop the technology to make this medically possible.
"I think within five years we could have an implant which is ready for people," said Dr. Jackson in the press release. "Much of the technology we used for this is already being used separately in patients today, and has been proven to work. We just needed to bring it all together."
Here's a video of Jackson discussing the experiment: