Johns Hopkins researchers have begun genetically modifying adult cells to create balls of neurons that may serve as “mini-brains,” potentially good for preclinically studying—in petri dishes rather than in animals—Alzheimer’s, Parkinson’s, autism and the effects of drugs, for starters.

The balls are, in fact, 350-micrometer clusters of induced pluripotent stem cells (iPSCs).

Which is to say they’re fully adult cells that have been “reprogrammed” to behave like embryonic stem cells, then stimulated to grow into “brains” no bigger than the eye of a housefly, according to the Hub, Johns Hopkins’s news and information website.

After about two months’ time in the lab, the mini-brains developed four types of neurons and two types of support cells.

They also responded in a brain-like way to electrophysiological activity as drugs were introduced into them.

“Ninety-five percent of drugs that look promising when tested in animal models fail once they are tested in humans at great expense of time and money,” Thomas Hartung, MD, told the Hub.

The outlet reports that Hartung is applying for a patent and plans to launch a startup to put the mini-brains on the market, with hopes of seeing them “in as many labs as possible.”

“While rodent models have been useful, we are not 150-pound rats,” says Hartung. “And even though we are not balls of cells either, you can often get much better information from these balls of cells than from rodents.”