How to build a brain-machine interface

April 25, 2014 by Valerie Thompson, National Science Foundation
Developed in part with support from the National Science Foundation, the Argus II Retinal Prosthesis System works by bypassing damaged cells in the retina, transmitting images from a small camera to an implant in the back of the eye that sends electrical signals to the brain. Credit: Second Sight Medical Products

Devices that tap directly into the nervous system can restore sensation, movement or cognitive function. These technologies, called brain-machine interfaces or BMIs, are on the rise, increasingly providing assistance to people who need it most. But what exactly does it take to build a BMI?

To understand how (and why) BMIs are developed, the engineers who created the artifical retina can provide a kind of "how-to" guide for the curious and technically inclined.

While a greater understanding of biology has been essential to BMI development, advances in engineering and materials science have led to their design and performance. From creating new materials that are more compatible with the human body, to designing smaller electronics and better sensors, engineers are playing a major role in the development of existing and future brain technologies.

Like any other engineering challenge, building a BMI involves background research, feasibility testing, prototyping and production.

But building a BMI is unique in that engineers must design these devices to seamlessly interface with another complex system: the human nervous system.

The model: The bionic eye

In 2013, the U.S. Food and Drug Administration approved the Argus II Retinal Prosthesis System for use in individuals who have lost their vision as a result of severe-to-profound . A genetic condition affecting one in every 4,000 individuals, early symptoms of retinitis pigmentosa often include night blindness, followed by gradual but progressive loss of peripheral vision and ultimately total blindness.

The system works by bypassing damaged photoreceptors, cells in the retina that normally convert light into electrical signals that the brain interprets as visual information. The Argus II transmits images from a small camera to an implant in the back of the eye. Like the photoreceptors, the implant produces electrical signals that are transmitted to the brain.

"Seeing my grandmother go blind motivated me to pursue ophthalmology and to develop a treatment for patients for whom there was no foreseeable cure," says the device's co-inventor, Mark Humayun, associate director of research at the Doheny Retina Institute at the University of Southern California.

Without this motivation, the daunting design challenges and constraints might have been enough to make even the most meticulous researcher think twice about tackling such a project.

"The was a great engineering challenge under the interdisciplinary constraints of biology, enabling technology, [and] regulatory compliance" says Humayun's collaborator Wentai Liu, a professor of biomedical engineering at the University of California, Los Angeles.

In addressing such a challenge, before researchers begin to worry about the technological details, they must first determine whether a BMI is the right fit.

Step one: Decide if a condition is a good candidate for a BMI

Like most engineering endeavors, the first step in building a BMI has more to do with understanding the system at hand than with cutting-edge design.

When it came to creating an artificial retina, this meant that researchers needed to determine which parts of the visual pathway were working and which were not.

"We needed to know there were enough neurons left in the eye to stimulate and still transmit nerve impulses and communicate with the vision center of the brain," Humayun says.

With initial funding in the late 1980s and early 1990s from the National Eye Institute, the National Retinitis Pigmentosa Foundation and others, the researchers showed that neurons in the retina were still capable of responding to electrical stimulation—a sign that patients with this disease could potentially benefit from a BMI. If the nerves had been damaged, then signals would not have had a path to the brain, meaning that an artificial eye alone would not have solved the problem.

Step two: Determine if a fix is feasible

Once a condition is identified as a good candidate for a BMI, investigators need to determine whether the basic technologies needed to create such a device are even feasible.

For Humayun and colleagues, this meant tackling some tough engineering challenges, including how to mimic photoreceptor activity with artificial electrical stimulation, how to power the implant and enable real-time data transmission and how to integrate external components with the implant.

With early support from the National Science Foundation and others, the researchers set about answering each of these questions throughout the 1990s, meticulously developing prototypes of the miniature video camera and belt-worn computer that would capture and convert visual information, the integrated computer chip that would wirelessly receive the data and the tiny electrode array that would stand in for the damaged photoreceptors.

Step three: Consider the human factor

When designing a BMI, it's critical to remember that these devices must operate in concert with the human body. In addition to incorporating feedback from potential users throughout the design process, this means that the device must be designed in such a way that it can function effectively in the presence of body fluids and tissues.

Humayun and his collaborators addressed this challenge by creating a hermetically sealed packaging system that would allow the device to work in the gelatinous environment of the eye. They also carefully planned how they would implant the device to minimize the disruption to the body.

"The inside of the eye is a relatively immune-privileged site and the scarring reaction is minimal," Humayun says. "But, having said this, the surgery and the attachment of the device inside the eye has to be performed in the least invasive manner possible."

Step four: Optimize, shrink and integrate

Before a BMI reaches the end user, each component must be optimized, miniaturized and integrated with the rest of the device.

Unlike traditional design practices, which focus on optimizing each component, the artificial retina was developed by tweaking and streamlining the device as a whole, known as systems-level optimization.

The result? A sleek, small system that packs a punch.

"The engine for the artificial retina is a 'system on a chip' of mixed voltages and mixed analog-digital design, which provides self-contained power and data management," Liu says.

Step five: Scale up and get the go-ahead

One of the final steps in building a BMI is getting it into the hands of those who need it. When the initial technology is developed in an academic research setting, this can often mean handing it off to a company that will facilitate manufacturing and manage clinical trials and commercial distribution to patients.

Founded in 1998 by Humayun's former graduate student Robert Greenberg, Second Sight Medical Products Inc., took the artificial retina from the laboratory bench to the marketplace. Clinical trials for the first-generation device (the Argus I) were conducted in 2002, and were followed by pilot studies and patient trials for the Argus II in 2006. On Feb. 14, 2013, the Argus II became the first visual prosthesis to receive market approval in the United States.

Step six: Rinse and repeat

Perhaps the most important aspect of building a BMI is recognizing that there is always room for improvement.

"While we are still at the earliest stages, people are already benefiting from these implants, through improved mobility," says James Weiland, former deputy director of the Biomimetic Microelectronic Systems (BMES) Engineering Research Center at the University of Southern California.

"Working on advanced technology projects convinces me that it is feasible to create the technology needed for better outcomes."

Led by Humayun, the BMES Engineering Research Center was founded in 2003 to continue to advance the development of this technology. The latest prototype features an ultra-miniature camera that can be implanted directly in the eye. The system also contains more than 15 times the number of electrodes in the Argus II, which the researchers anticipate will greatly improve image resolution.

Explore further: Artificial retina receives FDA approval

Related Stories

Artificial retina receives FDA approval

February 14, 2013
The U.S. Food and Drug Administration (FDA) granted market approval to an artificial retina technology today, the first bionic eye to be approved for patients in the United States. The prosthetic technology was developed ...

Eye implants make vision-restoring progress

July 18, 2012
(Medical Xpress) -- "I was blind once but now I can see.” The words are no longer the sole property of religious testimony and literature. Medical progress is being made in the restoration of vision as evidenced by Second ...

New device offers hope to people blinded due to incurable eye disorders

November 17, 2013
Research presented at the 117th Annual Meeting of the American Academy of Ophthalmology shows promising data about a device that helps people who have lost their vision due to a blinding genetic disease to recognize common ...

Engineer invents bionic eye to help the blind

March 25, 2013
(Medical Xpress)—For UCLA bioengineering professor Wentai Liu, more than two decades of visionary research burst into the headlines last month when the FDA approved what it called "the first bionic eye for the blind."

Man among first in US to get 'bionic eye' (Update)

April 23, 2014
A degenerative eye disease slowly robbed Roger Pontz of his vision. Diagnosed with retinitis pigmentosa as a teenager, Pontz has been almost completely blind for years. Now, thanks to a high-tech procedure that involved the ...

Recommended for you

Researchers devise decoy molecule to block pain where it starts

January 16, 2018
For anyone who has accidentally injured themselves, Dr. Zachary Campbell not only sympathizes, he's developing new ways to blunt pain.

Scientists unleash power of genetic data to identify disease risk

January 16, 2018
Massive banks of genetic information are being harnessed to shed new light on modifiable health risks that underlie common diseases.

Blood-vessel-on-a-chip provides insight into new anti-inflammatory drug candidate

January 15, 2018
One of the most important and fraught processes in the human body is inflammation. Inflammatory responses to injury or disease are crucial for recruiting the immune system to help the body heal, but inflammation can also ...

Molecule produced by fat cells reduces obesity and diabetes in mice

January 15, 2018
UC San Francisco researchers have discovered a new biological pathway in fat cells that could explain why some people with obesity are at high risk for metabolic diseases such as type 2 diabetes. The new findings—demonstrated ...

Obese fat becomes inflamed and scarred, which may make weight loss harder

January 12, 2018
The fat of obese people becomes distressed, scarred and inflamed, which can make weight loss more difficult, research at the University of Exeter has found.

Optimized human peptide found to be an effective antibacterial agent

January 11, 2018
A team of researchers in the Netherlands has developed an effective antibacterial ointment based on an optimized human peptide. In their paper published in the journal Science Translational Medicine, the group describes developing ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.