Mini-brains made from teeth help reveal what makes us sociable

Can tiny brains grown in a dish reveal the secrets of sociability? Balls of brain tissue generated from stem cells are enabling us to understand the underlying differences between people who struggle to be sociable and those who have difficulty reining themselves in. 

Alysson Muotri at the University of California, San Diego, and his team created the mini-brains by exposing stem cells taken from the pulp of children’s milk teeth to cocktails of growth factors that help them mature.

Eventually, they can develop as many as six layers of cerebral cortex – the outer surface of the brain. This region is much more sophisticated in humans than in other animals, and houses important circuitry governing our most complex thoughts and behaviours, including socialising with others.

Each mini-brain is approximately 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 condition characterised by a hyper-sociable nature. People with Williams syndrome can be unable to restrain themselves from 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 Williams syndrome children have an abnormally high number. When cells from the teeth of children with none of these conditions were used, the resulting mini-brains were somewhere in between these two extremes.