Dr. Sergiu Pasca, a neuroscientist, used to envy cancer specialists. They could get their hands on tumors for research, while Pasca could not directly study key portions of a living brain.
But these days, Pasca does the next best thing: He grows his own.
In his lab at Stanford University, thousands of whitish balls of human brain tissue float in hundreds of dishes. Each smaller than a pea, they were created from human skin cells, including some from people with autism. Each one carries the DNA of the person it came from, and each organized itself enough to form a part of the brain that interests Pasca.
He is hardly alone. Dozens of labs are growing lumps of human brain tissue for study, a practice that drew notice in 2013 when researchers said they had created "minibrains" that contained multiple major parts of the fetal organ.
Just to be clear: Although brain cells in the lab-grown tissues show some activity, nobody has created fully functioning, adult human brains. The versions reported in scientific journals mimic only one or more parts of a fetal brain. (An August announcement of a nearly complete brain comparable to a fetal one hasn't been backed up by a journal article yet, and experts are withholding judgment until they can see the details).
Scientists say the technology holds great potential for studying the roots of diseases like autism and schizophrenia, testing possible treatments and tackling basic questions about evolution.
It's part of a larger movement over the past few years to create "organoids," miniature versions of the body's organs or key parts of organs. Goals include studying disease, testing possible treatments and perhaps supplying replacements for transplants. Scientists have made organoids representing the intestine, prostate, kidney, thyroid, retina and liver.
This overall organoid approach "is a major change in the paradigm in terms of doing research with human tissues rather than animal tissues that are substitutes. ... It's truly spectacular," says Arnold Kriegstein, who studies the brain at the University of California, San Francisco.
Organoids "are poised to make a major impact on the understanding of disease, and also human development," he says.
To grow lumps of brain tissue, researchers can call on a technique that helped earn the Nobel prize in medicine in 2012. Virtually all cells of a person's body contain the same lineup of DNA. A skin cell differs from a brain cell because of differences in what genes were turned on, and when, during development. The breakthrough lab technique provides a way to turn skin cells back into blank slates called iPS cells, a form of stem cell.
These iPS cells can then be turned into any cell of the body, as they respond to nudges from chemical cues they are exposed to.
For years, scientists have used this approach to make brain cells and other cells that lie on the flat surfaces of lab dishes. The new wrinkle is to let the cells grow into three-dimensional clumps instead. They don't need much help to organize themselves.
"They start communicating and signaling with each other," Kriegstein said, specializing "in a way that starts looking like a developing human brain."
But the cells don't get cues from surrounding tissues that help an ordinary fetal brain organize itself, noted Madeline Lancaster of the Medical Research Council Laboratory of Molecular Biology in Cambridge, England. So while the 400 or so tiny "minibrains" floating in dishes at her lab contain many brain parts, she said, those parts are laid out in abnormal patterns.
"They are connecting to each other and the different regions do seem to talk to each other, but not in the way a normal brain would," she said.