Blind People Could ‘see’ Letters That Scientists Drew On Their Brains With Electricity

August 5, 2020

Scientists sent patterns of electricity to people’s brains, inducing them to see letters that weren’t there.

According to the study, published today (May 14) in the journal Cell, the experiment worked in both people with normal vision and in participants who went blind as adults. While the technology is still in its early stages, the implanted devices could potentially be used in the future to stimulate the brain and restore people’s vision to some extent.

These implants, called visual prostheses, are placed on the visual cortex and then stimulated in a pattern that “tracks” the shapes that participants can “see”. More advanced versions of these implants can work similarly to cochlear implants, using electrodes to stimulate nerves in the inner ear to help enhance the wearer’s ability to hear.

“Early iterations [of this device] could provide detection of the contours of the shapes encountered,” study authors neuroscientist Michael Beauchamp and Baylor College of Medicine neurosurgeon Dr. Daniel Yoshor told Live Science in an email. yoshor will be at the University of Pennsylvania this summer. (Perelman School of Medicine begins new position).” The ability to detect forms of family members or allow for more independent navigation would be a wonderful advancement for many blind patients.”

The current study represents a small step toward making this technology a reality.

Look at the stars.
The study authors made the letters by stimulating the brain with an electrical current that causes it to produce what are called phosphenes – tiny spots of light that people can sometimes perceive without any actual light entering their eyes. Unlike light that bounces off objects in the room and into your eyes, phosphenes appear as a quirk of the visual processing system; you “see” these spots of light even though they aren’t actually there. For example, when you’re rubbing your eyes in a dark room, you may have seen phosphenes, a phenomenon often described as “seeing stars,” the authors say.

Known as “mechanical phosphorescence,” the stars that appear when you rub your eyes were first described by an ancient Greek philosopher and physiologist named Alcmaeon, said John Pezaris, head of the Visual Prosthetics Laboratory at Massachusetts General Hospital and an assistant professor of neurosurgery at Harvard University. Centuries later, in 1755, French physician Charles Leroy discovered that stimulating the brain with electricity could also produce vivid phosphorescence, even in blind people, said Pezaris, who was not involved in the study.

Scientists began running the idea of visual prosthetics in the 1960s, Pezaris said, when researchers implanted electrodes in the visual cortex – an area of the brain that processes incoming information from the eyes – with the goal of generating phosphorescent bodies and assembling them into coherent shapes. The scientists hypothesized that if they stimulated multiple points on the cortex, multiple phosphenes would appear and “automatically coalesce” into intelligible forms, like individual pixels on a computer screen, the authors noted.

“But the brain is far more complex than a computer display, and for reasons we don’t yet fully understand, it’s actually difficult to generate recognizable forms from combinations of phosphenes,” Beauchamp and Yoshor said. The authors encountered the same obstacle in their own research, but found ways to circumvent it.

Using the brain
The team laid a series of electrodes on the visual cortex of five study participants, three of whom were sighted and two of whom were blind. Specifically, these electrodes were located in an area of the brain known as V1, where information from the retina is channeled for early processing. Individuals with normal vision have undergone surgery to have electrodes implanted in their brains as part of their epilepsy treatment, designed to monitor epileptic activity in their brains. Blind people took part in another study investigating visual prosthetics and had the electrodes implanted at that time.

V1 works like a map, with different areas of the map corresponding to different areas of our field of vision, such as the top right or bottom left. The authors found that if they activated one electrode at a time, participants could reliably see a single phosphene (pinpoint spot) appear in its predicted region. However, if multiple electrodes came online at the same time, the individual phosphenes still appeared, but did not come together as a coherent shape.

So the authors tried a different strategy, where they hypothesized that by “sweeping an electric current across” several electrodes, they could trace patterns across the surface of the brain to produce recognizable shapes. The authors say, “The brain has a unique ability to tune in and detect changes in our environment.” As a result, they theorize, the organ should track the phosphene patterns presented one after another.

Pieter Roelfsema, director of the Netherlands Institute for Neuroscience, who was not involved in the study, told Live Science in an email that the cochlear implant uses a similar strategy to produce different auditory tones.” Suppose electrode 1 gives a high tone and electrode 2 gives a somewhat lower tone,” he said. By directing the current through both electrodes, “you can get a tone that is somewhere between electrode 1 and 2.”

The study authors found that they could do something similar with vision, where they could create phosphorene between the positions of two separate electrodes, thus connecting the dots between them. Using this technique, the authors drew letter shapes such as “W,” “S,” and “Z” on the surface of V1; these shapes had to be drawn backwards and upside down, which is how visual information usually travels from our eyes to the visual cortex.

Finally, the study participants could see the traced shapes and reproduce them accurately on the touch screen. When the study participants began to see the letters forming in their minds, “I think they were at least as excited as we were, probably more so!” Beauchamp and Yoshor told Live Science.

looking forward
In a letter in the journal Cell accompanying the new paper, Roelfsema writes that “there are still challenges to overcome” before the research can be applied to useful visual prostheses.

In the future, the authors say, visual prosthetics will likely contain “thousands of electrodes,” whereas this study used only a few dozen. In addition, “these electrodes may be designed to penetrate the cortex, bringing the electrode tips closer to neurons located a few hundred microns below the surface of the cortex,” they added.

Electrodes that penetrate the brain would produce a more precise phosphorescence than the weak electric field required for surface electrodes, Pezaris said. He noted that surface electrodes use strong electric fields to reach brain cells within tissues, sometimes leading to simultaneous stimulation of adjacent or overlapping cells.

Roelfsema told Live Science that for the visual prosthesis to work, new electrodes need to be invented that remain compatible with brain tissue over time. He said: “The current ones that go into the brain cause damage and don’t work long enough.” For some patients, however, surface electrodes may be best, depending on the risks associated with implanting them deep into their brains, Pezaris said. There are “many different causes of blindness,” he said, and some patients may benefit most from deeply implanted electrodes, others from surface electrodes, and still others from direct implantation of a retinal prosthesis that can be implanted with only eye surgery.

Most importantly, “for visual prosthetic devices to be truly useful for blind patients, they must improve quality of life,” Beauchamp and Yoshor said. That means that in addition to optimizing the physical electrodes and the way they operate, the scientists must also develop reliable software to help users filter and process visual information. And once assembled, the complete system must be useful enough for people to actually use it.

“Fundamentally, one of the things we have to keep in mind is that blindness is not a life-threatening disease, so the risks need to be balanced out with enough benefits,” Pezaris said of the visual prosthesis.