An excerpt from Michael Chorost's new book, in the NYT:
In Ramez Naam’s book More Than Human I learned of an idea that had been proposed by Rodolfo Llinás, a New York University neuroscientist. It was hair-raising. He suggested that engineers could bundle thousands of slender wires into a cable and insert it into the femoral artery in the groin. They would snake the cable through the bloodstream to the brain, as if doing an angiogram. As the cable entered the brain, the wires would spread out so that each one ended up in a capillary. Once put in place, each wire could detect a single neuron’s firing, and change its firing by pulsing a jolt of electricity to it.
Imagine it: a flower blossoming inside the brain, nanometer stalks splitting away from a micrometer stem. Expanding into every available capillary, touching every cubic millimeter of the brain, collecting terabytes of data in every second. By the same token, it could send in terabytes of data every second. It would be the most intimate interface ever invented. If you connected one person’s wired brain to another person’s, you could literally connect them together; they would have a real corpus callosum joining them (albeit with links of radio waves rather than wires.) And if you connected a number of people to each other via the Internet, then you would have a network in which each node was a human brain. The World Wide Web would become the World Wide Mind.
You wouldn’t think there’s room inside your capillaries to insert any kind of wire, but there is. As the image above shows, each nanowire is less than a micron (a millionth of a meter) across—substantially narrower than a capillary. Llinás’s lab has shown that it can be done in principle. They inserted platinum nanowires into the capillaries of tissue samples and detected the activity of neurons lying next to them. Power tends to dissipate rapidly from extremely thin wires, but researchers are trying, with some success, to create wires that can carry the necessary levels of current.
Larger-scale technologies already exist. Doctors can now thread a tube from the groin into the brain to inject anticancer drugs into tumors. These devices, called microcatheters, are thousands of times wider than nanowires, at half a millimeter to a millimeter in diameter. Nonetheless, they show that it’s possible to go deeply into the brain by threading a wire through the bloodstream. In an article on microcatheters the New York Times quoted a doctor as saying, “Technically, I can go anywhere in your brain.”
Of course, anyone can see problems with using large numbers of nanowires in a living brain. How does one guide thousands of wires through tangled kinks of capillaries? (Brain capillaries are as gnarled and twisted as baobab tree branches.) How does one get each one of them to a specific location? What if the wires get tangled? How do you keep them from shorting each other out? What about blood clotting? What if a wire goes through a capillary wall?
But virtually all of these objections were raised against cochlear implants in the 1970s.