Neuroscientists Restored Movement to Paralyzed Monkey Hands

Restoring movement to patients suffering paralysis is one of the greatest challenges facing modern medicine, and a new paper presents promising results in monkeys that could soon be transferred to humans.

A team at Newcastle University successfully restored the ability of two macaque monkeys to grasp an object with their own paralysed hand. (The monkeys’ hands weren’t permanently paralysed; they were given a drug called muscimol that temporarily mimics the effect of a stroke in terms of disrupting the pathways from the brain to the spinal cord that cause paralysis. It wears off after a couple of hours and the monkeys’ hand function is restored to normal.)

The researchers used electrical stimulation to achieve this, which we’ve seen used before to allow paralysed patients to move external devices like computer cursors and avatars, robotic arms, and exoskeletons like that set to take the first kick of the World Cup. The new idea here is that the implanted electrodes actually allow the patient to move their own limbs.

Andrew Jackson, who co-authored the paper in Frontiers in Neuroscience with colleague Jonas Zimmermann, explained in a phone call that after a stroke or spinal cord injury, the parts of the patient’s brain upstream of the injury may function normally, and their limbs below may still have the capacity to work too—the problem is the connection between the two.

“The idea of the research was to see if we could artificially reconnect the brain to the spinal cord, bypassing a potential site of injury,” he said.

They inserted electrodes via fine metal wires into the premotor cortex of the brain and relayed information from there down to more electrodes in the spinal cord that activated circuits to perform a grasping action. The monkeys were trained to grasp and pull an orange disc, and the researchers would turn the electrical connection on and off. When the stimulation was turned on, the monkeys’ brain activity as they tried to grasp the disc was relayed via the electrodes to the muscles, and they could do it.

There’s a few caveats: Jackson emphasised that grasping is a very simple behaviour, and the monkeys weren’t able to do it to their usual level with the treatment. “But we were able to restore their ability to do this task in a way that they weren’t able to do the task when the stimulation was turned off,” he said. And though simple, it could be a useful movement for human patients.

To get to that point, work needs to be done, but the use of brain signals to control robot prosthetics and of implanted electrodes on the spinal cord for clinical uses like chronic pain management lay a good groundwork. “So at least in part some of these techniques are already getting into patients; what we’re looking to do is to sort of link them up,” said Jackson.

They’re now working on shrinking down the bank of electronics they used, with the aim of developing a small battery-powered device that could be implanted under the skin. They also need to demonstrate that the technique can be used over a long period of time, and not just in short bursts. Judging by the broader field and the time it takes to get methods tested on animals into humans, Jackson suggested a time-frame of around five years.