Mini-Brains Grown in a Lab Have Human-Like Brain Activity

A new study promises new paths to research mental illness, but raises questions about whether so-called organoids could develop consciousness

Brain organoids in a dish. Credit: Muotri Lab-UCTV

Alysson Muotri was dumbfounded when the pea-sized blobs of human brain cells that he was growing in the lab started emitting electrical pulses. He initially thought the electrodes he was using were malfunctioning.

Muotri was wrong. What the cells were emitting were brain waves — rhythmic patterns of neural activity. “That was a big surprise,” he says.

The 3D blobs of brain cells, known as organoids, are commonly used in disease and drug research to replicate organs. But no “mini-brain” had ever shown signs of brain waves before.

That was in 2016. Now, Muotri and his colleagues at the University of California, San Diego, have detailed their findings on the organoids in a new study in the journal Cell Stem Cell.

Scientists are a long way from understanding the human brain. Organoids that emit brain waves could open up new opportunities for research. But as mini-brains become better replicas for real brains, they raise ethical questions about where sentience begins, and whether these blobs of tissue need protections of the sort offered to animals and humans in research.

Muotri’s team grew organoids by first programming adult skin cells into stem cells that have the ability to specialize into any cell type. With the right cocktail of chemicals and growth factors to stimulate cell growth, Muotri and his team were able to coax the cells into becoming different types of neurons. With this recipe, they grew hundreds of organoids that were more mature than previous models.

Using electrodes, they first detected bursts of brain waves at about two months. As the organoids grew, they produced brain waves at different frequencies, and the signals became more regular, suggesting the neurons were forming connections. Then, at about 10 months, the neural activity plateaued. Muotri says that might be due because additional neurons are needed to continue development or that some of the cells in the organoids start to die off after 10 months.