I’m going to let you in on a secret. Every cell in your body has the potential to get smarter. I don’t mean this metaphorically, or in a “body keeps the score” kind of way. I mean that if lab-coated biologists took a sample of your skin and very carefully manipulated the cells inside it, they could actually make a brain. They do it all the time.
Not a brain as complex as the one behind your eyes, of course, but a glob of gray matter nonetheless, with a few-million-odd neurons that can send and receive electrical signals. Biologists call these strange creations human brain organoids. Kept at a womblike 98.6 degrees Fahrenheit for eight months, they’ll produce repetitive oscillations—brain waves—nearly indistinguishable from those made by a premature baby.
In cell culture labs around the world, human brain organoids live out their short lives as neural guinea pigs, testing the effects of diseases, toxins, and new pharmaceuticals. But they may soon be on to more glamorous pursuits. At the University of San Diego, organoids are guiding spidery robots through mazes and taking hero doses of psychedelics. At Johns Hopkins, they’re forming the basis of novel biocomputing systems. And at a startup in Melbourne, they’re playing video games like Pong and Doom.
Biologists do the darnedest things. While the rest of us are distracted by large language models and AI agents, they’re going straight to the source of intelligence, cultivating living neurons and teaching themselves to program them with electrical signals and hits of dopamine. In the future, they wager, artificial intelligence won’t be artificial at all. It’ll be built from the stuff of life itself.
The most metal building at UC San Diego is the library. An inverted concrete ziggurat, the Geisel Library—named for the children’s author better known as Dr. Seuss—looms over an otherwise bucolic campus on spindly, two-story legs. On a recent afternoon, as a marine layer hung low in the eucalyptus groves, it looked particularly like the mothership of a brutalist alien race.
That day, the Geisel’s sunken lobby was hung with scientific images from the university’s collection. Among CGI renderings of folded proteins and macrophotographs of benthic sea creatures, one image stuck out. It depicted a clump of human brain cells, silhouetted in black against the milky white of a petri dish. A corona of axons, the threadlike nerve endings that transmit electrical impulses across the brain, stretched outward from the clump with palpable yearning.
Whether in our skulls or in a dish, neurons want nothing more than to find one another—and, across the emptiness, to forge the synapses whose electrical chattering forms the basis of thought. They’re very good at it. If you put loose brain cells together, they will multiply and interlink until they’ve cohered into autonomous globs of tissue. Human brain organoids practically make themselves.
A 20-minute walk from the Geisel, at UCSD’s Sanford Stem Cell Institute, they’re making themselves in the tens of thousands. “Whatever environment you put them in, the first thing that they do is try to connect,” said the Brazilian developmental biologist Alysson Muotri, as we gazed over the blue plane of Pacific outside his office window. “Connect with the dishes, connect with the electrodes, connect to each other. This is an intrinsic property of our brain, to connect.”
Muotri is dashing, with a surfer’s tan and the aquiline profile of a figure on an ancient Roman coin. Over the past decade, his lab has dramatically expanded the scope of brain organoid research. He and his colleagues have revived genetic material from the hominin fossil record to create “Neanderthalized” brain organoids. They have sent organoid payloads to the International Space Station to study what cosmic radiation does to astronaut brains. But the issue closest to Muotri’s heart is autism. His 18-year-old son is autistic and receives 24-hour care. By studying brain organoids grown from the cells of autistic donors—including his son—he hopes to pinpoint where the neural development of autistic children differs from their neurotypical counterparts.
This is not an invasive procedure. To make a brain organoid, all you need is that sample of skin I mentioned before. (Samples of blood, hair, or teeth work too.) You take the adult cells and introduce them to some special proteins that revert them to their embryonic state. Given a second chance to mature, these so-called induced pluripotent stem cells can become anything: tear gland organoids that cry, heart organoids that beat, or brain organoids that … well, that’s the question.
In utero brain development is, as one bioethicist told me, “a black box” of scientific knowledge. Historically, a lot of what we know about it is inferred from studies with mice. But with an organoid, the transformation of stem cells into neurons into brain tissue happens in full view. In theory, scientists could one day study how a colony of dividing cells comes together to create a mind—to make, from 86 billion neurons, a person named Alysson Muotri, for example.
Or another one named Claire L. Evans, who at this moment is leaning over Muotri’s shoulder to gape at a dish of floating brainlets under the microscope. Visually, organoids are not compelling; they’re opaque, snot-colored, the approximate size and shape of a chia seed. Muotri’s organoids contain 5 million cells, of which 2.5 million are neurons. (The rest are non-neural glial cells, which serve as scaffolding.) This, he reassures me, is the size of a bee’s brain. I suspect this is his way of tempering any ethical ick I may have. Although the evidence for insect sentience is growing, invertebrate research is still exempt from federal animal welfare laws. As John Evans, a sociologist and the codirector of UCSD’s Institute for Practical Ethics, put it to me when I wandered over to his office for the humanist take, “You don’t need to get permission to torture as many flies as you want.”
For now, you don’t need permission to torture brain organoids either. From a bioethical perspective, they aren’t people; they’re not even animals. If organoids someday graduate from bee to mouse size, this protocol would have to evolve. The trouble is, nobody knows quite where to draw a line. Sentience is hardly a settled idea; it’s not even clear you can have sentience without a body or a sensory experience of the world. And forget about calling an organoid conscious. “Imagine that you had spent your life in a glass tube—could you possibly even think of what you have as consciousness?” Evans asked me. “Philosophers of mind will tell you that what we call consciousness is not possible without experiences.” To make a conscious organoid, he added, “you first have to start having organoids have experiences.”
This isn’t impossible. We’ve all seen The Matrix. To the brain, the whole Ferris wheel of life is just pings of chemistry and electricity. To give an organoid an “experience,” all Muotri has to do is pluck one from its amniotic goo, place it on a conductive sheet of graphene, and—not to put too fine a point on it—zap it.
Do the organoids like being zapped? Muotri isn’t sure. What he does know is that they respond to electrical signals, remember them, and eventually come to anticipate them. For him, that’s evidence that they’re maturing, becoming more useful models of human development. But for other researchers, this electrical communication represents something else entirely: that living matter, like a computer, is programmable. And this is where things get truly weird.
It’s 3:30 pm in Los Angeles, which means it’s tomorrow morning in Australia. I’m sitting on the fire escape of my office building, peering at a grid of 59 squares on my laptop screen. I’ve been told that each of the squares represents an electrode in the Melbourne laboratory of the biocomputing startup Cortical Labs. And on each of those electrodes is a tiny culture of living human neurons. At the moment, my screen is registering fleeting spikes from those neurons—the spontaneous activity of brain matter in a vacuum. I click a square, zapping off an electrical hello to neurons 8,000 miles away. In response, all 59 electrodes spike at once.
For a moment, I’m giddy with a feeling of new power. I click around, sending those distant neurons hopping; my screen fills with the peaks and valleys of their electrical pulses. I page over to the neurons’ environmental settings. If I wanted to, I could drop their onboard temperature or nuke their precise gas mix of oxygen and CO2. If I did that, they’d certainly die. It’s about as significant a paradigm shift as I can imagine for computing: No matter how badly you mess up your code, things on the computer don’t normally die in real life.
But that’s the reality of the Cortical Cloud. In Melbourne, Cortical Labs cultivates flat neural cultures—the stem cells were donated by the company’s own founder—and loads them into sleek white biological “computers” called CL-1s. Each is the size of an elongated toaster and boasts an onboard life-support system capable of keeping a culture of up to a million neurons alive for six months. With the CL-1, Cortical Labs is aiming to become the Nvidia of neural computing, providing hardware and, let’s say, “neurons as a service” with a sub-millisecond delay.
For now, these neural computers are mostly of interest to researchers who want to work with neurons without taking on the tedious wet-lab husbandry themselves. Eventually, however, the company hopes that neurons will prove themselves to be an energy-efficient, resilient substrate for more general computing applications—including some tasks currently handled by AI, like image recognition and classification.
“When you think about what you want from AI, it’s biology,” said Brett Kagan, Cortical Labs’ chief operating officer, when I reached him over Zoom. “You want it to be self-repairing as much as possible. You want it to be adaptable. You want it to be long-lived. You want it to be energy-efficient. These are all features you get for free in biology.”
Kagan is a new father; as we spoke, his toddler ran riot in the background. But he’s no stranger to young and unruly forms of intelligence. In 2022, using a system similar to what currently powers the Cortical Cloud, Kagan grew a neural culture on a microchip and trained it to play the 1972 Atari game Pong, rewarding the neurons with predictable electrical pulses when they made correct decisions and punishing them with chaotic bursts when they made mistakes.
The technique served as a minimal proof of concept for a theory, proposed by the neuroscientist Karl Friston, that self-organizing biological systems tend to minimize surprise whenever possible. By showing that neurons will reorganize themselves to avoid chaotic stimulus, Cortical Labs demonstrated one possible approach for programming living matter. But the experiment also signaled that the CL-1 could be considered hardware for testing theories of cognition. “Not to try and make our stuff sound so grandiose,” Kagan told me, “but I would say the CL-1 is to theoretical neuroscience as the Large Hadron Collider was to theoretical physics.”
Kagan, to be fair, enjoys a grandiose claim. In the Pong paper, he and his colleagues claimed that the neurons, “embodied” within the game, displayed a form of sentience. Many in the research community balked at this cavalier use of language; one particularly polemic response, published in the journal Neuron, accused Cortical Labs of “hijacking” the very concept of sentience.
But as Alon Loeffler, a scientist at Cortical Labs, later explained to me, our brains are embedded in an environment, and responding to that environment in real time is what brains do—it’s what brains are for. Since neurons in a dish don’t benefit from those constant feedback loops of action and experience, the game fills the gap. “A game is just a version of the world,” Loeffler said.
The Pong program comes preinstalled on the Cortical Cloud, as a package of easily deployable Python code. When I ran the Australian neurons through a two-hour session, I watched as they incrementally improved their game in real time. In the end, their longest rally was 10 accurate shots, which beats my tennis game handily. It was impressive, but now the neurons are leveling up.
When I set out to report this story, I was sure it was about consciousness: the eerie moment a quarter-peanut of flesh sparks with self-knowledge, and what that precipice means for the researchers responsible. I imagined long dark nights of the cell and tiny funerals for spent neurons. What I found, however, was that nearly all scientists who keep organoids see the consciousness question as a distraction.
Most bristle when asked. They gesture to the organoids themselves—tiny balls bobbing in liquid solution like droplets of olive oil in vinegar—as if to say, give me a break. “Consciousness is so qualitative,” complained Annie Kathuria, an organoid researcher, when I visited her lab at Johns Hopkins. “How am I supposed to measure something qualitative on a tissue that’s floating in a dish? Someone has to define it. That’s what I say to everyone: Define to me what consciousness is, in quantitative terms.”
The request is rhetorical, of course. Humans have been trying to define consciousness since the days of Plato and nobody’s come close to nailing down the general idea, let alone a list of quantitative metrics. But it reflects a strong tendency in biology labs to want to focus on the practical, rather than the philosophical. When I spoke to Kathuria, she sipped from a Venti Starbucks tea and regularly glanced at the whiteboard over my shoulder, covered in a list of dozens of drug screenings her lab was on the hook for. Defining the nature of mind was the last thing on her mind.
