Neuroscience

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Ars chats with Precision, the brain-chip maker taking the road less invasive

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Brain-chip buzz —

Precision tested its BCI on 14 people so far. Two more are scheduled this month.

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Precision’s Layer 7 Cortical Interface array.

Enlarge / Precision’s Layer 7 Cortical Interface array.

Work toward brain-computer interfaces has never been more charged. Though neuroscientists have toiled for decades to tap directly into human thoughts, recent advances have the field buzzing with anticipation—and the involvement of one polarizing billionaire has drawn a new level of attention.

With competition amping up in this space, Ars spoke with Ben Rapoport, who is a neurosurgeon, electrical engineer, and co-founder of the brain-computer interface (BCI) company Precision Neuroscience. Precision is at the forefront of the field, having placed its BCI on the brains of 14 human patients so far, with two more scheduled this month. Rapoport says he hopes to at least double that number of human participants by the end of this year. In fact, the 3-year-old company expects to have its first BCI on the market next year.

In addition to the swift progress, Precision is notable for its divergence from its competitor’s strategies, namely Neuralink, the most high-profile BCI company and headed by Elon Musk. In 2016, Rapoport co-founded Neuralink alongside Musk and other scientists. But he didn’t stay long and went on to co-found Precision in 2021. In previous interviews, Rapoport suggested his split from Neuralink related to the issues of safety and invasiveness of the BCI design. While Neuralink’s device is going deeper into the brain—trying to eavesdrop on neuron signals with electrodes at close range to decode thoughts and intended motions and speech—Precision is staying at the surface, where there is little to no risk of damaging brain tissue.

Shallow signals

“It used to be thought that you needed to put needle-like electrodes into the brain surface in order to listen to signals of adequate quality,” Rapoport told Ars. Early BCIs developed decades ago used electrode arrays with tiny needles that sink up to 1.5 millimeters into brain tissue. Competitors such as Blackrock Neurotech and Paradromics are still developing such designs. (Another competitor, Synchron, is developing a stent-like device threaded into a major blood vessel in the brain.) Meanwhile, Neuralink is going deeper, using a robot to surgically implant electrodes into brain tissue, reportedly between 3 mm and 8 mm deep.

However, Rapoport eschews this approach. Anytime something essentially cuts into the brain, there’s damage, he notes. Scar tissue and fibrous tissue can form—which is bad for the patient and the BCI’s functioning. “So, there’s not infinite scalability [to such designs],” Rapoport notes, “because when you try to scale that up to making lots of little penetrations into the brain, at some point you can run into a limitation to how many times you can penetrate the brain without causing irreversible and undetectable damage.”

Further, he says, penetrating the brain is just unnecessary. Rapoport says there is no fundamental data that suggests that penetration is necessary for BCIs advances. Rather, the idea was based on the state of knowledge and technology from decades ago. “It was just that it was an accident that that’s how the field got started,” he said. But, since the 1970s, when centimeter-scale electrodes were first being used to capture brain activity, the technology has advanced from the macroscopic to microscopic range, creating more powerful devices.

“All of conscious thought—movement, sensation, intention, vision, etc.—all of that is coordinated at the level of the neocortex, which is the outermost two millimeters of the brain,” Rapoport said. “So, everything, all of the signals of interest—the cognitive processing signals that are interesting to the brain-computer interface world—that’s all happening within millimeters of the brain surface … we’re talking about very small spatial scales.” With the more potent technology of today, Precision thinks it can collect the data it needs without physically traversing those tiny distances.

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The nature of consciousness, and how to enjoy it while you can

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Remaining aware —

In his new book, Christof Koch views consciousness as a theorist and an aficionado.

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A black background with multicolored swirls filling the shape of a human brain.

Unraveling how consciousness arises out of particular configurations of organic matter is a quest that has absorbed scientists and philosophers for ages. Now, with AI systems behaving in strikingly conscious-looking ways, it is more important than ever to get a handle on who and what is capable of experiencing life on a conscious level. As Christof Koch writes in Then I Am Myself the World, “That you are intimately acquainted with the way life feels is a brute fact about the world that cries out for an explanation.” His explanation—bounded by the limits of current research and framed through Koch’s preferred theory of consciousness—is what he eloquently attempts to deliver.

Koch, a physicist, neuroscientist, and former president of the Allen Institute for Brain Science, has spent his career hunting for the seat of consciousness, scouring the brain for physical footprints of subjective experience. It turns out that the posterior hot zone, a region in the back of the neocortex, is intricately connected to self-awareness and experiences of sound, sight, and touch. Dense networks of neocortical neurons in this area connect in a looped configuration; output signals feedback into input neurons, allowing the posterior hot zone to influence its own behavior. And herein, Koch claims, lies the key to consciousness.

In the hot zone

According to integrated information theory (IIT)—which Koch strongly favors over a multitude of contending theories of consciousness—the Rosetta Stone of subjective experience is the ability of a system to influence itself: to use its past state to affect its present state and its present state to influence its future state.

Billions of neurons exist in the cerebellum, but they are wired “with nonoverlapping inputs and outputs … in a feed-forward manner,” writes Koch. He argues that a structure designed in this way, with limited influence over its own future, is not likely to produce consciousness. Similarly, the prefrontal cortex might allow us to perform complex calculations and exhibit advanced reasoning skills, but such traits do not equate to a capacity to experience life. It is the “reverberatory, self-sustaining excitatory loops prevalent in the neocortex,” Koch tells us, that set the stage for subjective experience to arise.

This declaration matches the experimental evidence Koch presents in Chapter 6: Injuries to the cerebellum do not eliminate a person’s awareness of themselves in relation to the outside world. Consciousness remains, even in a person who can no longer move their body with ease. Yet injuries to the posterior hot zone within the neocortex significantly change a person’s perception of auditory, visual, and tactile information, altering what they subjectively experience and how they describe these experiences to themselves and others.

Does this mean that artificial computer systems, wired appropriately, can be conscious? Not necessarily, Koch says. This might one day be possible with the advent of new technology, but we are not there yet. He writes. “The high connectivity [in a human brain] is very different from that found in the central processing unit of any digital computer, where one transistor typically connects to a handful of other transistors.” For the foreseeable future, AI systems will remain unconscious despite appearances to the contrary.

Koch’s eloquent overview of IIT and the melodic ease of his neuroscientific explanations are undeniably compelling, even for die-hard physicalists who flinch at terms like “self-influence.” His impeccably written descriptions are peppered with references to philosophers, writers, musicians, and psychologists—Albert Camus, Viktor Frankl, Richard Wagner, and Lewis Carroll all make appearances, adding richness and relatability to the narrative. For example, as an introduction to phenomenology—the way an experience feels or appears—he aptly quotes Eminem: “I can’t tell you what it really is, I can only tell you what it feels like.”

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Sleeping more flushes junk out of the brain

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Better sleep on it —

Rhythmic activity during sleep may get fluids in the brain moving.

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Abstract image of a pink brain against a blue background.

As if we didn’t have enough reasons to get at least eight hours of sleep, there is now one more. Neurons are still active during sleep. We may not realize it, but the brain takes advantage of this recharging period to get rid of junk that was accumulating during waking hours.

Sleep is something like a soft reboot. We knew that slow brainwaves had something to do with restful sleep; researchers at the Washington University School of Medicine in St. Louis have now found out why. When we are awake, our neurons require energy to fuel complex tasks such as problem-solving and committing things to memory. The problem is that debris gets left behind after they consume these nutrients. As we sleep, neurons use these rhythmic waves to help move cerebrospinal fluid through brain tissue, carrying out metabolic waste in the process.

In other words, neurons need to take out the trash so it doesn’t accumulate and potentially contribute to neurodegenerative diseases. “Neurons serve as master organizers for brain clearance,” the WUSTL research team said in a study recently published in Nature.

Built-in garbage disposal

Human brains (and those of other higher organisms) evolved to have billions of neurons in the functional tissue, or parenchyma, of the brain, which is protected by the blood-brain barrier.

Everything these neurons do creates metabolic waste, often in the form of protein fragments. Other studies have found that these fragments may contribute to neurodegenerative diseases such as Alzheimer’s.

The brain has to dispose of its garbage somehow, and it does this through what’s called the glymphatic system (no, that’s not a typo), which carries cerebrospinal fluid that moves debris out of the parenchyma through channels located near blood vessels. However, that still left the questions: What actually powers the glymphatic system to do this—and how? The WUSTL team wanted to find out.

To see what told the glymphatic system to dump the trash, scientists performed experiments on mice, inserting probes into their brains and planting electrodes in the spaces between neurons. They then anesthetized the mice with ketamine to induce sleep.

Neurons fired strong, charged currents after the animals fell asleep. While brain waves under anesthesia were mostly long and slow, they induced corresponding waves of current in the cerebrospinal fluid. The fluid would then flow through the dura mater, the outer layer of tissue between the brain and the skull, taking the junk with it.

Just flush it

The scientists wanted to be sure that neurons really were the force that pushed the glymphatic system into action. To do that, they needed to genetically engineer the brains of some mice to nearly eliminate neuronal activity while they were asleep (though not to the point of brain death) while leaving the rest of the mice untouched for comparison.

In these engineered mice, the long, slow brain waves seen before were undetectable. As a result, the fluid was no longer pushed to carry metabolic waste out of the brain. This could only mean that neurons had to be active in order for the brain’s self-cleaning cycle to work.

Furthermore, the research team found that there were fluctuations in the brain waves of the un-engineered mice, with slightly faster waves thought to be targeted at the debris that was harder to remove (at least, this is what the researchers hypothesized). It is not unlike washing a plate and then needing to scrub slightly harder in places where there is especially stubborn residue.

The researchers also found out why previous experiments produced different results. Because the flushing out of cerebrospinal fluid that carries waste relies so heavily on neural activity, the type of anesthetic used mattered—anesthetics that inhibit neural activity can interfere with the results. Other earlier experiments worked poorly because of injuries caused by older and more invasive methods of implanting the monitoring hardware into brain tissues. This also disrupted neurons.

“The experimental methodologies we used here largely avoid acute damage to the brain parenchyma, thereby providing valuable strategies for further investigations into neural dynamics and brain clearance,” the team said in the same study.

Now that neurons are known to set the glymphatic system into motion, more attention can be directed towards the intricacies of that process. Finding out more about the buildup and cleaning of metabolic waste may contribute to our understanding of neurodegenerative diseases. It’s definitely something to think about before falling asleep.

Nature, 2024.  DOI: 10.1038/s41586-024-07108-6

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