Waldau got the idea from his work treating a rare disorder called Moyamoya disease. Patients have blocked arteries at the base of their brain, keeping blood from reaching the rest of the organ. “We sometimes lay a patient’s own artery on top of the brain to get the blood vessels to start growing in,” says Waldau. “When we replicated that process on a miniaturized scale we saw these vessels self-assemble.”

While it wasn’t clear from this experiment whether or not there was rodent blood coursing through its capillaries—the scientists had to flush them to accomplish fluorescent staining—the UC Davis team did demonstrate that the blood vessels themselves were comprised of human cells. Other research groups at the Salk Institute and the University of Pennsylvania have successfully transplanted human organoids into the brains of mice, but in both cases, blood vessels from the rodent host spontaneously grew into the transplanted tissue. When brain balls make their own blood vessels, they can potentially live much longer by hooking them up to microfluidic pumps—no rodent required.

That might give them a chance to actually mature into a complex computational organ. “It’s a big deal,” says Christof Koch, president of the Allen Institute for Brain Science in Seattle, “but it’s still early days.” The next problem will be getting these cells wired into circuits that can receive and process information. “The fact that I can look out at the world and see it as spatially organized—left, right, near, far— is all due to the organization of my cortex that reflects the regularity of the world,” says Koch. “There’s nothing like that in these organoids yet.”

Not yet, maybe, but it’s not too soon to start asking what happens when they do. How large do they have to be before society has a moral mandate to provide them some kind of special protections? If an organoid comes from your cells, are you then its legal guardian? Can a brain ball give its consent to be studied?

Just last week the National Institutes of Health convened a neuroethics workshop to confront some of these thorny questions. Addressing a room filled with neuroscientists, doctors, and philosophers, Walter Koroshetz, director of the NIH’s National Institute of Neurological Disorders and Stroke, said the time for involving the public was now, even if the technology takes a century to become reality. “The question here is, as those cells come together to form information processing units, when do they get to the point where they’re as good as what we do now in a mouse? When does it go beyond that, to information processing you only see in a human? And what type of information processing would be to a point where you would say, ‘I don’t think we should go there’?”

Of course, that assumes that neuroscientists would be able to recognize consciousness in an organoid if they saw it. Biology has yet to settle on a theory of consciousness in humans, let alone measure it in a ball of brain cells. Because, after all, a brain isn’t really a brain until has experience. You can have all the right wires and connections, but until it’s hooked up to some kind of input, it won’t process anything. Blood vessels are a good start—but we won’t start worrying about consciousness until the brain balls have eyes.

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