A group of Cambridge scientists are attempting to grow human brains outside of the body in a lab. But they don’t look anything like what you might imagine. The “cerebral organoids” are made with stem cells derived from human skin and raised in giant incubators. Without any kind of blood supply, they receive nutrients by soaking in a special fluid. And these brains are tiny, small enough to fit in a petri dish – about four millimeters across and crammed with about two million neurons. For the sake of comparison, a fully developed mouse brain contains four million neurons. The average adult human brain, up to 1,000 trillion.
Just like a normal brain, these bundles of cells contain a mixture of gray matter and white matter. They even form specific regions like the cortex, hippocampus, cerebellum, and many more. In the end, they are equivalent to what might be seen in a nine-week-old fetus.
However, while the neurons in these tiny organoids do communicate and fire with electrical activity, they aren’t capable of thoughts or feelings in the way we would understand it. Dr. Madeline Lancastercompares their neural activity to the way heart cells can be made to beat in a petri dish. While they are alive, the lack of a body or any sensory input means they aren’t receiving any of the information that could lead to consciousness. If lab-grown brains were hooked up to an EEG, no brain waves would be observed.
However, consciousness is not the goal of this research. Instead, Lancaster is interested in uncovering some key differences between humans and other primates. Our DNA is only 1.2 percent different from chimpanzees, yet somehow we have completely different intellectual capabilities. Her team is replacing individual genes involved in brain development with genes from chimpanzees, and observing how the replacements influence the growth of the specimens.
In other labs, organoids like these are being used to learn more about human development – for example, what makes the brain of someone with schizophrenia or autism different from a normal brain. The inability to identify these disorders in other animals has made researching them in the lab impossible. (And while there are a lot of reasons not to support animal testing, dissecting the brains of living humans is obviously unethical as well.)
Instead, researchers can use this technology and a stem cells from patients to learn more about how their neurons function. This has already led to some interesting insights into the development of autism, and will likely reveal even more hidden knowledge in time.