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Minuscule blobs of human brain tissue have come a long way in the four years since scientists in Vienna discovered1how to create them from stem cells.
The most advanced of these human brain organoids — no bigger than a lentil and, until now, existing only in test tubes — pulse with the kind of electrical activity that animates actual brains. They give birth to new neurons2, much like full-blown brains. And they develop the six layers3 of the human cortex, the region responsible for thought, speech, judgment, and other advanced cognitive functions.
These micro quasi-brains are revolutionizing research on human brain development and diseases from Alzheimer’s to Zika4, but the headlong rush to grow the most realistic, most highly developed brain organoids has thrown researchers into uncharted ethical waters. Like virtually all experts in the field, neuroscientist Hongjun Song of the University of Pennsylvania doesn’t “believe an organoid in a dish can think,” he said, “but it’s an issue we need to discuss.” . . [Full text]