Brain stent to let five paralysed people control exoskeleton
MIND CONTROL without the side effects. That’s the aim of a device that could help people control robotic limbs using thought alone – without the need for brain surgery. The device will be trialled in people with paralysis next year.
Several groups are developing brain-machine interfaces that allow people who are paralysed to operate a bionic exoskeleton just by thinking about it. These devices decode electrical brain signals and translate them into movement of robotic limbs.
Usually, brain signals are detected via electrodes attached to the scalp or implanted directly in the brain. Placing them on the scalp avoids surgery, but the signals are muffled by the skull. Direct implantation allows precise recordings but the electrodes can stop working because the brain treats them as foreign bodies and wraps them in scar tissue.
Now, a research team led by Thomas Oxley at the University of Melbourne has developed a way of implanting electrodes in the brain without opening up the skull.
Their electrodes are attached to a metallic mesh tube that is guided through a small incision in the jugular vein in the neck and up into a blood vessel in the brain. There, the electrode can measure signals from nearby brain cells on the other side of the vessel wall.
The technique is borrowed from cardiologists, who slide similar tubes called stents into arteries to keep them open.
The electrode-studded stent – or “stentrode” – was tested in the brains of live sheep in 2016 (Nature Biotechnology, doi.org/f8dczh). Like a cardiac stent, it sat in the blood vessel without causing any adverse effects. Because the metallic mesh does not directly touch brain tissue, no inflammation or scarring occurred over the six-month trial. “The brain doesn’t even know it’s there,” says David Grayden at the University of Melbourne, who oversaw the engineering of the device.
The matchstick-sized stentrode was able to clearly detect electrical brain signals. “The recordings are not quite as detailed as those from directly implanted electrodes, but they’re close,” says Grayden.
The team is now planning a clinical trial at the Royal Melbourne Hospital that will start next year. Up to five patients with no use of their arms or legs due to spinal cord injury, stroke, motor neurone disease or muscular dystrophy will be involved.
The stentrode will be inserted into a blood vessel that runs along the motor cortex, the part of the brain that controls movement. Fine wires will run from the electrodes down through the blood system into a recording device implanted in the chest. This device will then wirelessly transmit the information to an external computer.
“The end goal is that the person will be able to think about moving and an exoskeleton will obey”
By asking participants to think about a particular action, like “move right fist”, the computer will learn to recognise the exact pattern of brain signals corresponding to each thought.
“The end goal is that the person will be able to think about moving and an exoskeleton will obey,” says Grayden.
The research is exciting, but it’s still unclear whether the stentrode will be able to pick up meaningful signals in the brains of humans, says Nick Ramsey at University Medical Center Utrecht in the Netherlands. “The stentrode research is worth doing, but I would not dismiss the technologies that are already much further ahead.”
This article appeared in print under the headline “Brain control via blood vessel stent”
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