Although other scientists are using similar techniques on simpler problems, Johnson is the only person trying to make a commercial neurological product that would enhance memory. In a few minutes, he’s going to conduct his first human test. For a commercial memory prosthesis, it will be the first human test. “It’s a historic day,” Johnson says. “I’m insanely excited about it.”

For the record, just in case this improbable experiment actually works, the date is January 30, 2017.

At this point, you may be wondering if Johnson’s just another fool with too much money and an impossible dream. I wondered the same thing the first time I met him. He seemed like any other California dude, dressed in the usual jeans, sneakers, and T-shirt, full of the usual boyish enthusiasms. His wild pronouncements about “reprogramming the operating system of the world” seemed downright goofy.

But you soon realize this casual style is either camouflage or wishful thinking. Like many successful people, some brilliant and some barely in touch with reality, Johnson has endless energy and the distributed intelligence of an octopus—one tentacle reaches for the phone, another for his laptop, a third scouts for the best escape route. When he starts talking about his neuroprosthesis, they team up and squeeze till you turn blue.

And there is that $800 million that PayPal shelled out for Braintree, the online-­payment company Johnson started when he was 29 and sold when he was 36. And the $100 million he is investing into Kernel, the company he started to pursue this project. And the decades of animal tests to back up his sci-fi ambitions: Researchers have learned how to restore memories lost to brain damage, plant false memories, control the motions of animals through human thought, control appetite and aggression, induce sensations of pleasure and pain, even how to beam brain signals from one animal to another animal thousands of miles away.

And Johnson isn’t dreaming this dream alone—at this moment, Elon Musk and Mark Zuckerberg are weeks from announcing their own brain-hacking projects, the military research group known as Darpa already has 10 under way, and there’s no doubt that China and other countries are pursuing their own. But unlike Johnson, they’re not inviting reporters into any hospital rooms.

Here’s the gist of every public statement Musk has made about his project: (1) He wants to connect our brains to computers with a mysterious device called “neural lace.” (2) The name of the company he started to build it is Neuralink.

Thanks to a presentation at last spring’s F8 conference, we know a little more about what Zuckerberg is doing at Facebook: (1) The project was until recently overseen by Regina Dugan, a former director of Darpa and Google’s Advanced Technology group. (2) The team is working out of Building 8, Zuckerberg’s research lab for moon-shot projects. (3) They’re working on a noninvasive “brain–computer speech-to-text interface” that uses “optical imaging” to read the signals of neurons as they form words, find a way to translate those signals into code, and then send the code to a computer. (4) If it works, we’ll be able to “type” 100 words a minute just by thinking.

As for Darpa, we know that some of its projects are improvements on existing technology and some—such as an interface to make soldiers learn faster—sound just as futuristic as Johnson’s. But we don’t know much more than that. That leaves Johnson as our only guide, a job he says he’s taken on because he thinks the world needs to be prepared for what is coming.

All of these ambitious plans face the same obstacle, however: The brain has 86 billion neurons, and nobody understands how they all work. Scientists have made impressive progress uncovering, and even manipulating, the neural circuitry behind simple brain functions, but things such as imagination or creativity—and memory—are so complex that all the neuroscientists in the world may never solve them. That’s why a request for expert opinions on the viability of Johnson’s plans got this response from John Donoghue, the director of the Wyss Center for Bio and Neuroengineering in Geneva: “I’m cautious,” he said. “It’s as if I asked you to translate something from Swahili to Finnish. You’d be trying to go from one unknown language into another unknown language.” To make the challenge even more daunting, he added, all the tools used in brain research are as primitive as “a string between two paper cups.” So Johnson has no idea if 100 neurons or 100,000 or 10 billion control complex brain functions. On how most neurons work and what kind of codes they use to communicate, he’s closer to “Da-da” than “see Spot run.” And years or decades will pass before those mysteries are solved, if ever. To top it all off, he has no scientific background. Which puts his foot on the banana peel of a very old neuroscience joke: “If the brain was simple enough for us to understand, we’d be too stupid to understand it.”