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Technologies Seek to Bypass Nerve Damage in Paralyzed Patients

Researchers have developed a brain-machine interface (BMI) that allows monkeys to move two virtual arms just by thinking. A separate team of scientists has designed a device that mimics bladder function in paralyzed rats. Both technologies are wedded to the nervous system in a way that could potentially produce more natural, personalized control of sensory and motor function in paralyzed patients.

The studies, which appear in the 6 November issue of the journal Science Translational Medicine, highlight the future of neuroprosthetic and robotic technologies in human health.

The idea behind BMIs is to link the brain activity from imagined movements to a computerized device that enables actual movement. A person with a spinal cord injury can still think about moving his or her limbs, but because the spinal cord is disconnected from the brain, these actions cannot be carried out. BMIs aim to bypass the spinal cord to regain control of limb movement.

For the past decade, researchers have made steady progress in developing BMIs capable of connecting both monkey and human brains to a single prosthetic or virtual arm. But no BMI could be used to simultaneously control two virtual arms, until now. The BMI created by Peter Ifft at Duke University and colleagues does just that, by using brain signals from monkeys to control two virtual arms at the same time.

The researchers recorded the activity of nearly 500 neurons in two monkeys and, with the help of special algorithms, used these brain signals to create a robotic link that re-routed the neural commands to virtual arms. In the experiments, each monkey viewed two avatar arms on a computer monitor from a first-person perspective.

Two square targets appeared on the screen and the animals had to place the virtual hands over the squares and hold these positions for delayed intervals. Within two weeks of training, the animals realized that they didn’t need to move their real hands, and stared at the computer monitor without moving to control the virtual arms.

The two squares were then replaced by two circular targets in different positions (right, left, up, or down relative to a start position for each hand). At this point, the monkey had to place both avatar hands over the circles and hold these positions simultaneously for a minimum of one-tenth of a second to receive a fruit juice reward.

Taking a closer look, the researchers observed that the animals’ brains started firing in response to the touch of the virtual arms as if they were real arms. After a while, the virtual arms became “assimilated” to the monkeys’ brains like their own hands. The results should help scientists design future BMIs capable of helping human patients regain two-handed motor control.

In a separate study, Daniel Chew at the University of Cambridge and colleagues show that neuroprosthetics, long known for helping paralyzed individuals regain function of an arm or a leg, may soon be able to help control of organs like the bladder.

Normally, nerves sense when the bladder begins to fill up and electrochemically communicate this signal to the brain. But people with spinal cord injury can no longer feel their bladder or trigger urination due to the disrupted connection between the brain and the bladder’s sensory and motor nerves. These patients are forced to empty their bladders with catheters, without which the bladder fills up and causes a high pressure that can lead to severe kidney and bladder damage.

The electrode device developed by Chew and colleagues records sensory nerve information that deciphers when the bladder is filling, when it is full, and when it contracts. The researchers surgically implanted the device in the bladders of rats, and observed that the technology could successfully gauge when and how much the bladder was full in the animals. Furthermore, the device was able to both block and trigger bladder emptying on cue through electrical stimulation.

The device still has a long way to go before it is ready for human use (it must be miniaturized and made out of materials that work inside the human body), but in the future the authors envision a hand-held device that buzzes when a patient needs to go to the bathroom. Patients could then press on the implanted device to stimulate bladder emptying. The study sets the stage for more convenient, personalized control of bladder function in paralyzed patients.

The virtual monkey avatar, seen in third-person perspective, as the movements of the two arms are decoded in real-time from the brain of a rhesus monkey. | Duke Center for Neuroengineering