Neuroprosthetics — A Simple Guide from a Neuroscience Student

Neuroprosthetics explained by a fellow student to other students

We live in a truly amazing time. We can now attempt to give new eyes to the blind, new ears to the deaf, and new legs and arms to the injured. The potential for neuroprosthetics is unlimited and I believe that it will continue to become more and more important.

In this article, I hope to explain the history and the concepts behind neuroprosthetics using simpler terms for students and for those that are not well versed with neuroscience and neurotechnology.

When and how did this all begin?

One might imagine that mankind’s efforts to enhance, repair, or modify one’s nervous system are a recent phenomenon. Surprisingly, the oldest neuroprosthetics on record dates back to 1957, when a doctor operated on a deaf person in Paris in order to improve his hearing.

In the early 1960s, efforts by Blair Simmons, a professor in the department of otolaryngology at Stanford Medical School achieved a breakthrough in installing a cochlear implant. Using a 6-electrode array, Simmons and colleagues’ patient was able to identify the sound as speech by recognizing its different characteristics. Following Simmons’ experiments, more clinical trials have been conducted and the field started to become more widely accepted between the scientists and the clinicians.

Schematic of a cochlear implant

Now we jump 40 years into the future. Neuroprosthetics gained a huge public attention once again during the 2014 Brazil World Cup. Dr. Miguel Nicolelis’ lab at Duke University developed a neuroprosthetics device to allow a spinal-cord injured patient to kick off the World Cup.

World Cup exoskeleton allows paraplegic to walk again: Video by National Science Foundation

Since 2014, the technology has advanced rapidly and now we come to the time where neuroprosthetics is becoming more and more accessible to the general public. Frequently, you come across discussions about neuroprosthetics on online forums, social media, and public news. If you are curious, it might not be a bad idea to try to learn how neuroprosthetics actually work.

It’s cool and all but how do neuroprosthetics actually work?

In order to implement a neuroprosthesis, one must be able to detect and record the brain activity involved in the planning, and execution of movement intentions. For example, when we decide to grab a cup of coffee, there is a brain activity in areas that are important for the execution of coffee-grabbing behaviour (i.e. motor areas in the brain). By measuring this brain activity, we can relate the intent and the execution of the movement to the activity of the brain.

For example, one can use multiple electrodes to measure cortical activity.

After recording the brain signals, researchers have been able to analyze these signals to detect someone’s intentions and then relay these intentions to an external machine or a robot. The most simple recording technology one can use is electroencephalography (EEG). Using electrodes placed on a scalp, a researcher can identify different types of signals and determine which parts of the brain are active.

Now you might think that it can’t be this simple. You are absolutely right. A neuroprosthesis will not always behave accurately when it is first implanted into a subject. Imagine buying a new cell phone. You need to calibrate the settings to match your needs and fiddle around with the phone to really feel like the phone is now truly yours (almost like it’s part of your body!).

Not surprisingly, a neuroprosthesis works similarly. Scientists, clinicians, and the user must train the neuroprosthesis and calibrate the device so that it behaves like it belongs to the subject’s body.

One way of training a neuroprosthesis to learn optimal motor behaviours (as controlled by the subject) is by using a concept called error-related potential (ErrP). ErrP carries cognitive information about the accuracy of goal-directed movements. If the movement of the neuroprosthesis does not meet the subject’s expectations, ErrP can be detected.

From Iturrate et al. 2015

In this method, the subject evaluates the action performed by the neuroprosthesis and decides if the action was accurate or erroneous. The intent of the subject is obtained from the brain signals and relayed to the reinforcement learning algorithm implemented with the neuroprosthesis. Over time, the neuroprosthesis learns appropriate behaviours.

Until now, we talked about how the brain can control a robotic device. Then one might wonder if the brain can receive information from a robotic device. Imagine how it would feel if you can’t feel anything when you try to grab something. Let’s say that you won’t be able to feel how much pressure you are putting on, and the feeling of the object. It will probably be pretty difficult for you to pick up a paper cup full of hot water. Or it will also be frustrating to cook, or play sports.

If you have no pressure information, you might accidently crush a paper cup!

In order to deal with this problem, scientists have developed a way to allow a reversal transfer of information. This means that some devices can convert environmental stimuli into human perceptions. Reversal of information transfer is especially useful for limb (motor) prosthetics. In order to achieve an accurate movement, one requires feedback from its limbs. Recent developments in technology allow users of prosthetics to also feel tactile and pressure information.

Dr. Hugh Herr, who leads a Biomechatronics lab at MIT Media Lab have published a paper in 2017 that describes a technology called agonist-antagonist myoneural interface (AMI). AMI is used to enhance the sensory characteristics of a current neuroprosthetics. AMI is a unique surgical paradigm which utilizes a muscle graft along with neuroprosthesis in order to recreate the phenomenon of contraction and stretching in one’s muscles. This procedure has been found to regenerate some parts of the neuromuscular junction, which carries a huge clinical potential.

How we’ll become cyborgs and extend human potential: Video by TED

One big problem scientists had with neuroprosthetics was that it was really difficult to recreate the sensation of proprioception. As known as “proprioception, or the ‘perception or awareness of the position and movement of the body’”, is crucial for constructing a comprehensive system for neuroprosthetics.

Someone might wonder why we can’t detect the position of our body by just looking at our arm and tracking the location of our body parts. However, proprioception is a bit more delicate than that. Even if we can track the location of our leg, for example without proprioception, our unconscious mechanisms that control our movements (such as walking and running) would be affected. Furthermore, proprioception is important for the sense of body ownership. Meaning that without proprioception, you might think that your arms or your legs belong to someone else.

Man in this video (Ian Walterman) lost proprioception because of injury (BBC: The Man Who Lost His Body)

Without proprioception, one will have a hard time gauging the power, delicacy, and speed of their movements. Proprioception has also been shown to be important for the recovery of patients with a motor injury.

Then, were scientists able to recreate the sensation of proprioception using neuroprosthetics? AMI procedure was able to provide the subject with some senses of proprioception, which encourages the patient to recognize the neuroprosthetics as part of their body. Jim Ewing, who received the AMI surgery claims:

The morning after the first time I was attached to the robot, my daughter came downstairs and asked me how it felt to be a cyborg, and my answer was that I didn’t feel like a cyborg. I felt like I had my leg, and it wasn’t that I was attached to the robot so much as the robot was attached to me, and the robot became part of me. It became my leg pretty quickly.

I believe that very soon we will be able to use neuroprosthetics to completely recreate all sensations and help the patients feel like they have legs and arms again.

With the emergence of new technology and paradigms, neuroprosthetics is becoming more and more powerful, more accessible, and are giving hopes to amputees and injured individuals.

So what? Where is neuroprosthetics going and how can people benefit from this?

Neuroprosthetics have a huge clinical potential. Clinicians and scientists can utilize this technology to grant patients vision and hearing capabilities, as well as assist amputees and paralyzed patients. Neuroprosthetics have already been implemented successfully in many instances.

See Paralyzed man moves hand, Woman receives bionic hand with sense of touch, The new bionics that let us run, climb and dance.

As neuroprosthetics gain more popularity in the media, the cost of these prosthetics is likely to drop and become more available to the public. Unfortunately, the prices are currently a bit too high for everyone.

BiOM T2, which is a newer line of neuroprosthetics (ankle system) produced by Herr, lists for about $40,000. The system still might be too expensive for some users, although some companies have already agreed to include the BiOM T2 device in their workers’ compensation plan.

On a more positive note, according to a new report by Grand View Research, the global neuroprosthetics market is expected to reach $8 billion by 2020, meaning a 90% increase in market size from 2015 to 2020. Following this prediction, I hope to see more publicly funded neuroprosthetics projects in the future.

North America Neuroprosthetics Market Growth

As the neuroprosthetics market expand even further and new research suggests more potential for the technology, it will be really exciting to see where we will end up. Some companies and scientists are even turning to the idea of enhancing the human body. Lockheed Martin, a company based in Maryland, United States has been developing an exoskeleton technology called FORTIS to assist operators to use heavy tools with little effort. The potential for human enhancement and patient treatment is really exciting.

I am personally really excited to see what neuroprosthetics will become in 10 to 20 years. Will we be able to cure most amputees and patients? Will we even use neuroprosthetics to enhance bodily functions?

Now we’ll have to wait and see about that!

Suggestions for Further Reading and Videos



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Christopher An

Christopher An

Neuro and Math UGrad @McGillU. Now Neuroscience PhD Student at Johns Hopkins University. Interests in Plasticity, Sensory Processing, and Decision Making.