When Jan Scheuermann volunteered for an experimental brain implant, she had no idea she was making neuroscience history.
Scheuermann, 54 at the time of surgery, had been paralyzed for 14 years due to a neurological disease that severed the neural connections between her brain and muscles. She could still feel her body, but couldn’t move her limbs.
Unwilling to give up, Scheuermann had two button-sized electrical implants inserted into her motor cortex. The implants tethered her brain to a robotic arm through two bunches of cables that protruded out from her skull.
Scheuermann’s bet paid off. With just a few days of practice, she was able to bring a bar of chocolate to herself, using only her mind to control the prosthetic.
That was 2012. The field of brain-machine interface has been on fire ever since.
Prototype neuroprosthetics can already let the paralyzed walk and the blind see again—granted, the effects are still far from perfect. Various exoskeletons and retinal implants are steadily making their way through human trials, striving to reach mass market by the end of the decade. Future brain implants may be even bolder, helping restore memory loss in the elderly or giving healthy brains a boost.
But we’re not there yet. And electrodes—the heart of these devices—are partially to blame.
"Using electrodes to target specific brain circuits is like bringing a bazooka to an ant."
Most electrodes come in a stamp-sized array that activates any neuron in their vicinity. Using them to target specific brain circuits is like bringing a bazooka to an ant—you’ll get the target, but also stimulate thousands of other cells and potentially lead to unintended effects.
They also don’t like biological environments. Chemicals in the brain erode the electrodes over time, and the foreign implant often causes surrounding tissue to scar. Since scar tissue can’t conduct electricity, it renders the electrode useless.
To get around these issues, a team from Harvard and Palo Alto Research Center went back to the drawing board. Recently, they published research on a new type of implant made of tiny, thin copper coils embedded in silicon. Unlike its predecessors, the microcoil uses magnetic waves rather than electricity to stimulate the brain.
“We are pretty enamored by these coils right now,” lead author Dr. Shelley Fried remarked at the time. And indeed they are. In May, the team is testing their implant in the visual cortex of monkeys, Fried told Singularity Hub. The goal? To artificially recreate the activity patterns that normally come from the eyes—and have the monkeys “see” the world without ever using their sight.
Using magnets to tweak brain activity sounds bizarre, but scientists have long harnessed magnetic fields to treat severe depression and anxiety.
The therapy, transcranial magnetic stimulation (TMS), usually involves a figure-8 shaped wand that scientists wave over certain parts of the patients’ skull. The device delivers focused pulses of magnetic waves that travel through the skull and trigger tiny electrical fields. Depending on the orientation of the fields, they can either jolt or dampen the activity of select neurons.
Magnetic waves can also easily penetrate scar tissue, making them ideal for long-term use.
But TMS has a size problem. “Even the most precise TMS coils activate much larger regions without any selectivity,” says Fried. The roadblock has been making coils small enough to implant without losing efficacy.
Using an algorithm, the team played with different designs until they found the optimal device configuration: tiny metal coils, each thinner than a single strand of hair. Normally the coils are inert; when electricity passes through, they generate surprisingly strong magnetic fields—strong enough to stimulate neurons.
Because they were so small, the “microcoils allow for much finer control of activation,” to the point that the team could specifically control certain types of neurons within a thin vertical section of the cortex, explains Fried.
The coils were then wrapped in a biocompatible silicon sheath. This makes the brain less likely to attack the implant and decreases the chance of scarring.
The team first tested their device on slices of a mouse brain in a petri dish, to make sure that the microcoils could reliably activate neurons.
"The implant consistently worked like a dream: precise, responsive, and safe."
Then, using a thin, long needle, they inserted the coils into the area of the mouse brain that controls whisker movement. The coils were tethered to electrical cables to power them on, but later generations will likely utilize wireless technologies, says Fried.
When researchers activated the device, the mouse flicked its whiskers—forward, back or both ways—depending on the pattern of stimulation. In multiple trials, the implant consistently worked like a dream: precise, responsive, and safe.
Eye on the prize
The results were so promising that the team made immediate plans to collaborate with primate scientists and test the device on a therapeutic goal: restoring vision.
The new effort will be led by Dr. Richard Born, a neurobiologist at Harvard Medical School and one of the world's experts in primate visual cortex. Initial experiments will focus on using single microcoils to induce a broad sense of seeing light. If all goes well, the team will follow up with arrays of coils to try to induce more spatially complex patterns.
They’re entering a burgeoning field.
Several retinal prosthetics are already in development, all of which rely on electrode microarrays. These devices, though life changing, generally can only produce images that are grainy and black-and-white. Another potential therapy eschews implants altogether, instead looking to gene therapy and optogenetics to give blind patients back their vision—a cool idea, but one that comes with its own challenges.
"By artificially inputting activity into the visual cortex, we might be able to trick the brain into 'seeing' things without needing eyes."
The microcoil study stands out in its ambition. Rather than trying to replace the retina, the team is focusing on the final node of visual information processing: the visual cortex. The visual cortex is a master computer: it synthesizes all the information coming from the eyes and transforms electrical spikes into objects, faces and motion. That’s all vision is: patterns of activity.
By artificially inputting similar activity into the visual cortex, we might be able to trick the brain into “seeing” things without needing eyes. The idea’s been hard to test with electrodes, mostly because they lack finesse. Since electrodes often spread the activation to non-targeted neurons, they introduce so much noise to the images that they’re incomprehensible.
Because the activation they induce is so precise, microcoils may finally overcome this problem.
“Prosthetics implanted into the visual cortex can be used to treat a much wider range of visual dysfunctions than the retinal device,” says Fried.
Retinal prosthetics are mainly limited to outer retinal degenerative diseases. Cortical devices, in contrast, “can be used for just about all forms of blindness, including glaucoma, stroke and even traumatic eye injury,” she explains.
And vision’s only the first step.
If successful, the microcoils could be tested in other brain regions, such as those ravaged by Parkinson’s disease or depression. They could even be used to augment existing neural prostheses such as cochlear implants. Outside the brain, they could be used to stimulate the millions of neurons in the gut, which may help people with irritable bowl syndrome or even obesity.
Although microcoils are just beginning to be tested in primates, these applications may not be that far away. If the primate experiments are successful, the same technology will be optimized for human testing. The team hopes to begin human testing in 2018.
“I think it’s too early to say that coils are going to be the method of the future, but I think there’s definitely a possibility that they might,” says Fried.
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