Brain organoids are clusters of lab-grown brain cells that assemble themselves into structures that look a lot like human brain tissue. The process by which these cells become specialized and begin to communicate resembles the development of a human brain in the months before birth.

Brain organoids, often called "minibrains," have changed the way scientists study human brain development and disorders like autism. But the cells in these organoids differ from those in an actual brain in some important ways, scientists reported Wednesday in the journal Nature. The finding suggests that scientists need to be cautious about extrapolating results found in organoids to people, says Dr. Arnold Kriegstein, a professor of neurology at the University of California, San Francisco.