A 'visual prosthesis' implanted directly into the brain has allowed a blind woman to perceive two-dimensional shapes and letters for the first time in 16 years.
The US researchers behind this phenomenal advance in optical prostheses have recently published the results of their experiments, presenting findings that could help revolutionize the way we help those without sight see again.
At age 42, Berna Gomez developed toxic optic neuropathy, a deleterious medical condition that rapidly destroyed the optic nerves connecting her eyes to her brain.
In just a few days, the faces of Gomez' two children and her husband had faded into darkness, and her career as a science teacher had come to an unexpected end.
Then, in 2018, at age 57, Gomez made a brave decision. She volunteered to be the very first person to have a tiny electrode with a hundred microneedles implanted into the visual region of her brain. The prototype would be no larger than a penny, roughly 4 mm by 4 mm, and it would be taken out again after six months.
Unlike retinal implants, which are being explored as means of artificially using light to stimulate the nerves leaving the retina, this particular device, known as the Moran|Cortivis Prosthesis, bypasses the eye and optic nerve completely and goes straight to the source of visual perception.
After undergoing neurosurgery to implant the device in Spain, Gomez spent the next six months going into the lab every day for four hours to undergo tests and training with the new prosthesis.
The first two months were largely spent getting Gomez to differentiate between the spontaneous pinpricks of light she still occasionally sees in her mind, and the spots of light that were induced by direct stimulation of her prosthesis.
Once she could do this, researchers could start presenting her with actual visual challenges.
When an electrode in her prosthesis was stimulated, Gomez reported 'seeing' a prick of light, known as a phosphene. Depending on the strength of the stimulation, the spot of light could be brighter or more faded, a white color or more of a sepia tone.
When more than two electrodes were simultaneously stimulated, Gomez found it easier to perceive the spots of light. Some stimulation patterns looked like closely spaced dots, while others were more like horizontal lines.
"I can see something!" Gomez exclaimed upon glimpsing a white line in her brain in 2018.
Vertical lines were the hardest for researchers to induce, but by the end of training Gomez was able to correctly discriminate between horizontal and vertical patterns with an accuracy of 100 percent.
The Utah Electrode Array in action. (John A. Moran Eye Center at the University of Utah)
"Furthermore, the subject reported that the percepts had more elongated shapes when we increased the distance between the stimulating electrodes," the authors write in their paper.
"This suggests that the phosphene's size and appearance is not only a function of the number of electrodes being stimulated, but also of their spatial distribution… "
Given these promising results, the very last month of the experiment was used to investigate whether Gomez could 'see' letters with her prosthesis.
When up to 16 electrodes were simultaneously stimulated in different patterns, Gomez could reliably identify some letters like I, L, C, V and O. She could even differentiate between an uppercase O and a lowercase o.
The patterns of stimulation needed for the rest of the alphabet are still unknown, but the findings suggest the way we stimulate neurons with electrodes in the brain can create two-dimensional images.
The last part of the experiment involved Gomez wearing special glasses that were embedded with a miniature video camera. This camera scanned objects in front of her and then stimulated different combinations of electrodes in her brain via the prosthesis, thereby creating simple visual images.
The glasses ultimately allowed Gomez to discriminate between the contrasting borders of black and white bars on cardboard. She could even find the location of a large white square on either the left or right half of a computer screen. The more Gomez practiced, the faster she got.
The results are encouraging, but they only exist for a single subject over the course of six months. Before this prototype becomes available for clinical use it will need to be tested among many more patients for much longer periods of time.
Other studies have implanted the same microelectrode arrays, known as Utah Electrode Arrays, into other parts of the brain to help control artificial limbs, so we know they're safe in at least the short term. But it's still early days for the tech, which risks a steady drop in functionality over just a few months of operation.
While engineers beef up the reliability of the devices, we still need to know exactly how to program the software that interprets the visual input.
Last year, researchers at Baylor College of Medicine in Houston inserted a similar device into a deeper part of the visual cortex. Among five study participants, three of whom were sighted and two of whom were blind, the team found the device helped blind people trace the shapes of simple letters like W, S, and Z.
In Gomez's case, there was no evidence of the device triggering neural death, epileptic seizures, or other negative side effects, which is a good sign, and suggests microstimulation can be safely used to restore functional vision, even among those who have suffered irreversible damage to their retinas or optic nerves.
"One goal of this research is to give a blind person more mobility," says bioengineer Richard Normann from the University of Utah.
"It could allow them to identify a person, doorways, or cars easily. It could increase independence and safety. That's what we're working toward."
Right now, it seems only a very rudimentary form of sight can be returned with visual prostheses, but the more we study the brain and these devices among blind and sighted people, the better we will get at figuring out how certain patterns of stimulation can reproduce more complex visual images.
Perhaps one day, other patients in the future will be able to trace the whole alphabet with this prosthesis because of what Gomez has done. Four more patients are already lined up to try out the device.
"I know I am blind, that I will always be blind," Gomez said in a statement a few years ago.
"But I felt like I could do something to help people in the future. I still feel that way."
Gomez's name is listed as co-author on the paper for all her insight and hard work.
The study was published in the Journal of Clinical Investigation.
When it comes to the world of mammals, humans tend to stand out a fair bit.
While many animals share some aspects of our intelligence, they don't take it to the same level we have. But pinning down why we're more cognitively advanced on a neurological level has been tricky; to date, studies have found no significant differences between the brains of mammals. Now, we finally have a lead.
A team of researchers from the Massachusetts Institute of Technology (MIT) has found that, compared to other mammals, human brains have a much lower number of the neuronal channels that allow the flow of ions such as calcium, potassium, and sodium.
This flow produces the electrical impulses that allow neurons to communicate with each other; having fewer of them could mean that the human brain can operate more efficiently, diverting resources to more complex cognitive functions.
"Previous comparative studies established that the human brain is built like other mammalian brains, so we were surprised to find strong evidence that human neurons are special," says neuroscientist Lou Beaulieu-Laroche of MIT.
The seeds of the finding were planted in 2018, when Beaulieu-Laroche and his colleague Mark Harnet of MIT conducted a study comparing rat brains to human brains.
One of their findings concerned dendrites, the branching structures at the tips of nerve cells through which the brain's electrical impulses are received via ion channels. From here, the dendrite generates what we call an action potential, which transfers the signal onwards.
When comparing the brains of the two species, the researchers found that the human dendrites had a marked lower density of these ion channels compared to rat dendrites. This was worth investigating further.
The new research has been expanded to include 10 species: shrew, mouse, gerbil, rat, ferret, guinea pig, rabbit, marmoset, macaque and, of course, human, using samples of tissue excised from epilepsy patients during brain surgery.
An analysis of the physical structure of these brains revealed that ion channel density increases with neuron size, with one notable exception: the human brain.
This, the researchers concluded, was to maintain ion channel density across a range of brain sizes; so, although the shrew had a higher number of neurons than the rabbit or the macaque in a given volume of brain, the density of ion channels in that volume was consistent.
"This building plan is consistent across nine different mammalian species," Harnett said. "What it looks like the cortex is trying to do is keep the numbers of ion channels per unit volume the same across all the species. This means that for a given volume of cortex, the energetic cost is the same, at least for ion channels."
The exceptionally low ion channel density in the human brain was glaring, when compared with all the other brains.
All the comparison animals were significantly smaller than humans, of course, so it may be worth testing the samples of even larger animals. However, the macaque is often used in research as a model for the human brain.
The researchers suspect an evolutionary trade-off is possible for humans – this is when a biological system loses or diminishes a trait for an optimization elsewhere.
For example, it takes energy to pump ions through dendrites. By minimizing ion channel density, the human brain may have been able to deploy the energy savings elsewhere – perhaps in more complex synaptic connections, or more rapid action potentials.
"If the brain can save energy by reducing the density of ion channels, it can spend that energy on other neuronal or circuit processes," Harnett explains.
"We think that humans have evolved out of this building plan that was previously restricting the size of cortex, and they figured out a way to become more energetically efficient, so you spend less ATP [energy molecules] per volume compared to other species."
This finding reveals, the researchers said, an intriguing avenue for further investigation. In future research, the team hopes to explore the evolutionary pressures that might have led to this difference, and isolate where, exactly, that extra brain energy is going.
The research has been published in Nature.
