Clusters of human brain cells known as organoids have been successfully grown in a lab, according to a report researchers published in the journal “Cell Stem Cell” on Aug. 29.
These organoids, popularly known as “minibrains,” start as just a few stem cells in a petri dish. Over a period of months, they then grow into spheres the size of a pea and begin to look and act like human brain tissue. Although they aren’t able to grow larger than this, nor perform many of the functions that a human brain can, the organoids resemble the developing brain during pregnancy—specifically, they produce electrical signals called brain waves.
“After these organoids are in that six-to-nine-months range, that’s when [the electrical patterns] start to look a lot like what you’d see with a preterm infant,” said Alysson Muotri, director of the stem cell program at the University of California, San Diego.
As the organoids continued their growth, the electrical impulses grew in number and occurred at different frequencies. Eventually, researchers were able to determine that the brain cells were communicating with each other and forming neural networks.
“And what we could tell is not only the neurons are connecting to each other, but they are forming these microcircuitries,” said Muotri. “That’s when we started seeing these brain waves.”
To find out how closely the organoids resemble the human brain, the researchers trained a computer to compare the brain waves produced by the organoids with those of babies born up to three months prematurely. After 25 weeks of development, the machine could no longer determine which brain waves came from the human brain and which from the organoids.
This suggests that organoids could aid scientists in the study of conditions that have biological roots in the earliest phase of human brain development, such as schizophrenia and autism. Because these conditions begin before birth, it has previously been difficult to study their origins. A lab-grown minibrain, however, could viably be studied throughout years of its development.
The discovery, while important to the future of brain research, raises ethical questions as well.
“If we’re starting to see spontaneous brain activity that grows and develops as the organoid grows and develops, then we need to have some concerns about how ought we regard these things,” said Nita Farahany, professor of law and philosophy at Duke University. “Do they have some moral status?”
There do exist significant differences between the organoid and a human brain: although organoids are indeed becoming more complex and can live for many years in a lab, the human brain has a million times more cells and is able to not only perceive its environment through senses, but respond to it as well.
According to Farahany, who is on the National Institute of Health (NIH)’s Neuroethics Working Group, the NIH and other scientific organizations are working on developing ethical guidelines for researchers in this and related fields.
“If we don’t have good models to study the human brain, the potential for being able to address so much human suffering, disease, things that are very difficult to model in animals, we’ll never reach,” said Farahany. “So we have to figure out an ethical way to enable this research to progress.”