In lieu of blood supply, the mini-brains are being fed with a nutrient-rich fluid that is refreshed every few days. And since they don't have an immune system, everything that comes into contact with them needs to be disinfected first.
"The brains develop in the same way you would see in an embryo," Madeleine Lancaster, who heads the research at the Medical Research Laboratory of Molecular Biology in Cambridge, UK, told BBC.
The cerebral organoids are tiny - about four millimeters across - and crammed with about 2 million neurons (the average adult human has about 1,000 trillion neurons) firing information to each other. But like ordinary human brains, they are divided into grey matter and white matter and are even composed of specific regions: the cortex, the hippocampus, the cerebellum, and many others. According to Lancaster, they are equivalent to the brains of nine-week-old fetuses.
At the moment, the mini-brains are not capable of thinking yet, even if they are constantly buzzing with electrical activity. Lancaster compares them with heart cells that are coaxed to beat inside a petri dish.
"The neurons are working but they aren't really organized relative to one another," Lancaster said. Even if they are alive, they are not connected to a body that will supply them with information."
But the goal of the research is not to create conscious brains. According to Lancaster, the study is built towards uncovering the mystery behind humans' intellectual superiority by finding the key differences between humans and other primates.
Human DNA is only 1.2 percent different from that of chimpanzees, but both have different intellectual capabilities. Lancaster's team plans to replace individual genes related to brain development with the same type of genes from chimpanzees and observe how the replacements will influence the development of the specimens.
The organoids are also being used in studying neurological disorder, like autism and schizophrenia. Using these mini-brains, scientists hope to recreate the conditions in the brains of patients to find out what happens and what can be done to cure them.
"Our current interests focus on other neurodevelopmental disorders like autism and intellectual disability by introducing mutations seen in these disorders and examining their roles in pathogenesis in the context of organoid development," Lancaster said in the organoids project page. "Furthermore, we are studying cellular mechanisms underlying neurodevelopmental disease progression and potential therapeutic avenues."