BALLS of brain tissue grown from stem cells are helping us understand why some people struggle to be sociable and others can’t rein themselves in.
Alysson Muotri at the University of California, San Diego, and his team have created mini-brains from stem cells taken from the pulp of children’s milk teeth. These “organoids” can develop as many as six layers of cerebral cortex – the outer surface of the brain. The cortex houses circuitry governing our most complex thoughts and behaviours, including socialising.
Each mini-brain is roughly 5 millimetres across. “Though they’re not as well defined as they are in a real brain, they resemble what you find in an embryonic fetus,” says Muotri.
To understand how brain development affects sociability, the team used donated cells from children with autism and Rett syndrome, both of which are associated with impaired communication skills. They also used cells from children with Williams syndrome, a hyper-sociable condition in which people can be unable to resist talking to complete strangers.
The team found that mini-brains grown using stem cells from children with autism form fewer neural connections, while those from people with Williams syndrome have an abnormally high number. “The differences are striking, and go in opposite directions,” says Muotri. When the team examined donated brains from deceased people, they found similar patterns.
Research by other teams using organoids suggests that the brains of people with autism may also have a higher number of inhibitory neurons, cells that act to damp down the signals transmitted through the brain.
Muotri will discuss the results and the team’s future plans at a conference on stem cells in Olympic Valley, California, this week. Ultimately, he wants to understand how humans evolved to be so social, he says.
The team has already begun comparing human mini-brains with ones derived from bonobo and chimpanzee stem cells. “The most striking observation so far is that monkey brains mature way faster,” says Muotri.
Muotri is also planning to try connecting the organoids to rudimentary sense organs. The team wants to develop eye-like tissue that can sense light, and hook this up to the mini-brains. “We can then stimulate the eye and see what happens in the brain,” says Muotri.
But mini-brains have their limitations, says John Mason at the University of Edinburgh, UK. “The organoids are good for studying the very early stages of brain development, but may not reveal much about later stages on which things like sociality depend.”
This article appeared in print under the headline “Social brains grown in a dish”