Neuroprosthetic Limbs IMG 01

Neuroprosthetic Limbs: Exploring the Future of Prosthetics

Web Development Blog

Neuroprosthetic technology that allows for articulate prosthetic limbs controlled by the brain is advancing rapidly.

Every day, researchers at universities and private companies such as Elon Musk’s Neuralink announce new breakthroughs in mind-controlled technology.

In 2014 at the Brazil World Cup, a paraplegic named Juliano Pinto was able to perform the ceremonial first kick using an exoskeleton controlled by his brain. This YouTube video by the National Science Foundation explores how that was made possible:

Amputees are actively testing new neuroprosthetic limbs, though the technology still has some hurdles to cross to become viable to the public. Still, neuroprosthetics that allow wearers to experience touch and natural movement is coming ever closer to reality.

This post explores the current advances of neuroprosthetics and where the field is heading.

Exploring Neuroprosthetics and Brain-Computer Interface Technology

Neuroprosthetics are enabled by a brain-computer interface. This technology allows for input and/or output signals to travel between the brain and a machine.

Current myoelectric prosthetic arms already interpret signals from the brain through the muscles in a residual limb in order to perform the desired movement. Advances in neuroprosthetics are already allowing for devices in which wearers can control individual fingers in their prosthetic and/or experience tactile feedback.

An Italian woman recently tested a prototype neuroprosthetic hand that relayed signals to her nervous system regarding whether a touched object was hard or soft.

How Does Brain-Computer Interface Technology Work?

Neuroprosthetics are able to access the nervous system via electrodes attached to the wearer. Brain activity is mapped so the prosthetic will move based on the same signals that would control a biological limb. For tactile feedback, computing technology converts the tactile information from the prosthetic into signals for the brain.

Neuroprosthetic electrodes can be attached to the scalp, to peripheral nerves on the body, on the surface of the brain or even embedded in the brain itself. As you can imagine, each of these methods offers different benefits and come with different risks.

Scalp electrodes are the least invasive and use Electroencephalography (EEG) to read electrical activity in the brain. However, due to the barrier of the skin and skull, the brain waves interpreted by EEG only allow for simple control options.

In the case of the Italian woman with the neuroprosthetic hand, electrodes were implanted in the nerves of her upper arm. Electrodes implanted directly in the brain, also known as intraparenchymal electrodes, have allowed test subjects to control a prosthetic arm to drink from cups and pick up eggs. A major challenge to be solved in both of these cases is that the body’s immune system eventually causes degradation and loss of functionality of the electrodes.

While still invasive, electrodes on the surface of the cortex represent the middle road. They use a type of neural recording called electrocorticography (ECoG) to measure brain activity. A test subject at the University of Pittsburgh used this technology to control a 3D robotic arm:

Mapping the Brain and AI in Prosthetics

How do we get a prosthetic to learn to move based on the brain’s intention? There needs to be a training and calibration period, just like with current myoelectric prosthetics. With new AI technology, however, this machine learning process will become much quicker.

Current myoelectric calibration requires extensive work with a prosthetist and lots of trial and error. Future neuroprosthetics will use technologies like error-related potential (ErrP) to be able to assess via brainwaves whether the intended action was carried out. As a result, it will learn the wearer’s intention much quicker.

What Does The Future of Neuroprosthetics Look Like?

Hardware has already caught up to the point where we can create truly amazing prosthetics.

Hugh Herr is the head of MIT Media’s Biomechatronics group and a double leg amputee. He has created myoelectric bionic leg prostheses that move naturally based on environmental stimuli and signals from the residual leg. The team at MIT is now experimenting with growing nerves, transected nerves, through channels, or micro-channel arrays. These technologies would allow prosthetics to provide sensory feedback that feels like a natural limb.

Be sure to watch his inspiring TED Talk, which ends with a dance by a Adrianna Haslet-Davis, who lost her leg in the Boston Marathon attack:

The brain is a complex organism, and learning how to effectively establish two-way communication between it and a machine is not a simple task.

The stories and videos above show that scientists are hard at work on solving these life-changing problems. It won’t be long before we see examples of a neuroprosthetic limb that is almost indistinguishable to the wearer from a biological one.

Pictured: Les Baugh. Photo Credit: Johns Hopkins University Applied Physics Laboratory