Using electrodes, a computer, and the power of thought, neuroprosthetic devices can help patients with motor or sensory difficulties to move, feel, hear, and see.
Every year, hundreds of thousands of people worldwide lose control of their limbs as a result of an injury to their spinal cord. In the United States, up to 347,000 people are living with spinal cord injury (SCI), and almost half of these people cannot move from the neck down.
For these people, neuroprosthetic devices can offer some much-needed hope.
Brain-computer interfaces (BCI) usually involve electrodes - placed on the human skull, on the brain's surface, or in the brain's tissue - that monitor and measure the brain activity that occurs when the brain "thinks" a thought. The pattern of this brain activity is then "translated" into a code, or algorithm, which is "fed" into a computer. The computer, in turn, transforms the code into commands that produce movement.
Neuroprosthetics are not just useful for people who cannot move their arms and legs; they also help those with sensory disabilities. The World Health Organization (WHO) estimate that approximately 360 million people across the globe have a disabling form of hearing loss, while another 39 million people are blind.
For some of these people, neuroprosthetics such as cochlear implants and bionic eyes have given them back their senses and, in some cases, they have enabled them to hear or see for the very first time.
Here, we review five of the most significant developments in neuroprosthetic technology, looking at how they work, why they are helpful, and how some of them will develop in the future.
Probably the "oldest" neuroprosthetic device out there, cochlear implants (or ear implants) have been around for a few decades and are the epitome of successful neuroprosthetics.
The U.S. Food and Drug Administration (FDA) approved cochlear implants as early as 1980, and by 2012, almost 60,000 U.S. individuals had had the implant. Worldwide, more than 320,000 people have had the device implanted.
A cochlear implant works by bypassing the damaged parts of the ear and stimulating the auditory nerve with signals obtained using electrodes. The signals relayed through the auditory nerve to the brain are perceived as sounds, although hearing through an ear implant is quite different from regular hearing.
Although imperfect, cochlear implants allow users to distinguish speech in person or over the phone, with the media abound with emotional accounts of people who were able to hear themselves for the first time using this sensory neuroprosthetic device.
Here, you can watch a video of a 29-year-old woman who hears herself for the first time using a cochlear implant:
The first artificial retina - called the Argus II - is made entirely from electrodes implanted in the eye and was approved by the FDA in February 2013. In much the same way as the cochlear implant, this neuroprosthetic bypasses the damaged part of the retina and transmits signals, captured by an attached camera, to the brain.
This is done by transforming the images into light and dark pixels that get turned into electrical signals. The electrical signals are then sent to the electrodes, which, in turn, send the signal to the brain's optic nerve.
While Argus II does not restore vision completely, it does enable patients with retinitis pigmentosa - a condition that damages the eye's photoreceptors - to distinguish contours and shapes, which, many patients report, makes a significant difference in their lives.
Retinitis pigmentosa is a neurodegenerative disease that affects around 100,000 people in the U.S. Since its approval, more than 200 patients with retinitis pigmentosa have had the Argus II implant, and the company that designed it is currently working to make color detection possible as well as improve the resolution of the device.
Neuroprosthetics for people with SCI
Almost 350,000 people in the U.S. are estimated to live with SCI, and 45 percent of those who had an SCI since 2010 are considered tetraplegic - that is, paralyzed from the neck down.
Bill Kochevar had electrodes surgically fitted into his brain. After training the BCI to "learn" the brain activity that matched the movements he thought about, this activity was turned into electrical pulses that were then transmitted back to the electrodes in his brain.
In much the same way that the cochlear and visual implants bypass the damaged area, so too does this BCI area avoid the "short circuit" between the brain and the patient's muscles created by SCI.
With the help of this neuroprosthetic, the patient was able to successfully drink and feed himself. "It was amazing," Kochevar says, "because I thought about moving my arm and it did." Kochevar was the first patient in the world to test the neuroprosthetic device, which is currently only available for research purposes.
You can learn more about this neuroprosthetic from the video below:
However, this is not where SCI neuroprosthetics stop. The Courtine Lab - which is led by neuroscientist Gregoire Courtine in Lausanne, Switzerland - is tirelessly working to help injured people to regain control of their legs. Their research efforts with rats have enabled paralyzed rodents to walk, achieved by using electrical signals and making them stimulate nerves in the severed spinal cord.
"We believe that this technology could one day significantly improve the quality of life of people confronted with neurological disorders," says Silvestro Micera, co-author of the experiment and neuroengineer at Courtine Labs.
Recently, Prof. Courtine has also led an international team of researchers to successfully create voluntary leg movement in rhesus monkeys. This was the first time that a neuroprosthetic was used to enable walking in nonhuman primates.
However, "it may take several years before all the components of this intervention can be tested in people," Prof. Courtine says.
An arm that feels
Silvestro Micera has also led other projects on neuroprosthetics, among which is the arm that "feels." In 2014, MNT reported on the first artificial hand that was enhanced with sensors.
Researchers measured the tension in the tendons of the artificial hand that control grasping movements and turned it into electric current. In turn, using an algorithm, this was translated into impulses that were then sent to the nerves in the arm, producing a sense of touch.
Since then, the prosthetic arm that "feels" has been improved even more. Researchers from the University of Pittsburgh and the University of Pittsburgh Medical Center, both in Pennsylvania, tested the BCI on a single patient with quadriplegia: Nathan Copeland.
The scientists implanted a sheath of microelectrodes below the surface of Copeland's brain - namely, in his primary somatosensory cortex - and connected them to a prosthetic arm that was fitted with sensors. This enabled the patient to feel sensations of touch, which felt, to him, as though they belonged to his own paralyzed hand.
While blindfolded, Copeland was able to identify which finger on his prosthetic arm was being touched. The sensations he perceived varied in intensity and were felt as differing in pressure.
Neuroprosthetics for neurons?
We have seen that brain-controlled prosthetics can restore patients' sense of touch, hearing, sight, and movement, but could we build prosthetics for the brain itself?
Researchers from the Australian National University (ANU) in Canberra managed to artificially grow brain cells and create functional brain circuits, paving the way for neuroprosthetics for the brain.
By applying nanowire geometry to a semiconductor wafer, Dr. Vini Gautam, of ANU's Research School of Engineering, and colleagues came up with a scaffolding that allows brain cells to grow and connect synaptically.
Project group leader Dr. Vincent Daria, from the John Curtin School of Medical Research in Australia, explains the success of their research:
"We were able to make predictive connections between the neurons and demonstrated them to be functional with neurons firing synchronously. This work could open up a new research model that builds up a stronger connection between materials nanotechnology with neuroscience."
Neuroprosthetics for the brain might one day help patients who have experienced a stroke or who live with neurodegenerative diseases to recover neurologically.
Every year in the U.S., almost 800,000 people have had a stroke, and more than 130,000 people die from it. Neurodegenerative diseases are also widespread, with 5 million U.S. adults estimated to live with Alzheimer's disease, 1 million to have Parkinson's, and 400,000 to experience multiple sclerosis.