The minature brain sends out tendrils of neurons that cause the muscles to move, just like in the human body
Miniature brains grown in a petri dish (known as a cerebral organoid) are created using stem cells submerged in a vitamin-rich gel. The process allows scientists to explore some aspects of brain development– but not all. The miniature brains would die before they could develop beyond a set point because the gel cut off the oxygen supply.
This limited how much scientists could learn. They could, for instance, study how stem cells infected with microcephaly developed into a smaller brain mass. But there was not enough development to study more sophisticated processes, like the connections with the nervous system.
The Cambridge group figured out how to take a slice of the miniature brain and position it so it was both absorbing the gel in the petri dish and receiving oxygen. This allowed the miniature brain to develop for a full year, providing new insights into how the human brain is formed. Specifically, it gave the brain enough time to develop “tendrils” of neurons that linked up with a 1mm-long piece of spinal cord and back muscle (taken from a mouse embryo) in the petri dish. The brain then sent out electrical impulses, causing the muscles to twitch. The process mimicked how motor neurons work in the human body.