RACHEL MARTIN, HOST:
Clusters of human brain cells are providing some hints about the origins of disorders like autism and epilepsy. These cell clusters grow in a petri dish. And as NPR's Jon Hamilton reports, they develop in some of the same ways that a baby's brain does during pregnancy.
JON HAMILTON, BYLINE: Brain disorders often begin long before birth, but there's been no good way to see what's going awry as the brain goes through its early development. Then a few years ago, scientists figured out how to get human brain cells to grow in a dish and form three-dimensional structures the size of a pinhead. They were often called minibrains or brain organoids. Sergiu Pasca of Stanford University says scientists realized these clusters offered a new way to search for the origins of disorders like autism and epilepsy.
SERGIU PASCA: So the question was really, can we capture in a dish more of this elaborate processes that underline brain development and brain function?
HAMILTON: One key process involves neurons generated deep in the brain. The cells slowly migrate to areas near the surface, where they form networks that allow us to do things like planning and problem solving. Pasca led a team that set out to replicate some of this process in a petri dish. The team grew two types of clusters, representing both deep and surface areas of the forebrain. Then they put a deep cluster next to a surface cluster to see whether cells would start moving. Pasca says they did, in a surprising way.
PASCA: They don't just simply crawl, but they actually jump. So they - you know, they look for a few hours in the direction in which they want to move. They sort of decide on what they want to do, and then suddenly, they make a jump.
HAMILTON: Pasca suspected this migration process might be disrupted by an extremely rare genetic disorder called Timothy syndrome. Symptoms often include both autism and epileptic seizures. So Pasca repeated the experiment using cells that carried the Timothy syndrome mutation. And he says sure enough, the affected cells didn't jump as far as healthy cells did.
PASCA: So they would move a shorter distance. And overall, they would be sort of left behind in their migration.
HAMILTON: Pasca says that could disrupt normal brain development. These minibrains can't grow into anything like an actual brain. But Paola Arlotta says they are proving to be hugely important to researchers.
PAOLA ARLOTTA: One can really understand both a process of normal human brain development, which we frankly don't understand very well, but also make us understand what goes wrong in the brain of the patients affected by these prominent diseases.
HAMILTON: The brain cell clusters also offer a new way to test potential treatments. In the Timothy syndrome experiment, Pasca was able to use a drug to allow the defective cells to move normally. Arlotta says the challenge now is to create brain cell clusters that can live longer and include many more of the cell types found in a mature brain.
So far, her team has been able to sustain brain organoids for more than nine months. And she says when brain cell clusters live long enough, they spontaneously begin making connections, forming networks and creating new types of cells.
ARLOTTA: Using their own information from their genome, the cells can self-assemble. And they can decide to become a variety of different cell types that you normally find.
HAMILTON: She says the clusters have even produced nerve cells like those found in the retina. And like actual retinal cells, she says, they respond to light. Both Arlotta and Pasca's research appears in the journal Nature. Jon Hamilton, NPR News.