Clusters of living brain cells are teaching scientists about diseases like autism. With a new finding, some experts wonder if these organoids may become too much like the real thing.

Two hundred and fifty miles over Alysson Muotri’s head, a thousand tiny spheres of brain cells were sailing through space.

The clusters, called brain organoids, had been grown a few weeks earlier in the biologist’s lab here at the University of California, San Diego. He and his colleagues altered human skin cells into stem cells, then coaxed them to develop as brain cells do in an embryo.

The organoids grew into balls about the size of a pinhead, each containing hundreds of thousands of cells in a variety of types, each type producing the same chemicals and electrical signals as those cells do in our own brains. In July, NASA packed the organoids aboard a rocket and sent them to the International Space Station to see how they develop in zero gravity.

Now the organoids were stowed inside a metal box, fed by bags of nutritious broth. “I think they are replicating like crazy at this stage, and so we’re going to have bigger organoids,” Dr. Muotri said in a recent interview in his office overlooking the Pacific.

What, exactly, are they growing into? That’s a question that has scientists and philosophers alike scratching their heads.

On Thursday, Dr. Muotri and his colleagues reported that they have recorded simple brain waves in these organoids. In mature human brains, such waves are produced by widespread networks of neurons firing in synchrony. Particular wave patterns are linked to particular forms of brain activity, like retrieving memories and dreaming.

As the organoids mature, the researchers also found, the waves change in ways that resemble the changes in the developing brains of premature babies.

“It’s pretty amazing,” said Giorgia Quadrato, a neurobiologist at the University of Southern California who was not involved in the new study. “No one really knew if that was possible.”

But Dr. Quadrato stressed it was important not to read too much into the parallels. What she, Dr. Muotri and other brain organoid experts build are clusters of replicating brain cells, not actual brains.

“People will say, ‘Ah, these are like the brains of preterm infants,’” she said. “No, they are not.”

It’s been only six years since scientists created the first brain organoid from human skin cells. Now they’re being grown in laboratories around the world, offering scientists a new window onto the earliest stages of human brain development.

Here at U.C.S.D., researchers are using them to recreate, in miniature, inherited brain disorders and brain infections. They are also trying to grow bigger, more complex brain organoids. In one recent experiment, scientists linked a brain organoid and a spider-shaped robot, so that the two could exchange signals.

With Thursday’s report, published in the journal Cell Stem Cell, the question of what brain organoids might become is gaining more urgency.

“There are some of my colleagues who say, ‘No, these things will never be conscious,’” said Dr. Muotri. “Now I’m not so sure.”

Even if scientists someday produce only minimally self-aware organoids, that could represent a serious ethical concern, said Christof Koch, the chief scientist and president of the Allen Brain Institute in Seattle.

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