False color image of a slice of human brain organoid from a patient with autism spectrum disorder / Alysson Muotri
Scientists have created miniature brains from induced pluripotent stem cells that developed functional neural networks. And despite being a million times smaller than human brains, they produced brain waves resembling those of preterm babies.
The study in the journal Cell Stem Cell, could help scientists better understand human brain development.
"The level of neural activity we are seeing is unprecedented in vitro," says Alysson Muotri, a biologist at the University of California, San Diego. "We are one step closer to have a model that can actually generate these early stages of a sophisticated neural network."
The pea-sized brains, called cerebral organoids, are derived from human pluripotent stem cells. By putting them in culture that mimics the environment of brain development, the stem cells differentiate into different types of brain cells and self-organize into a 3D structure resembling the developing human brain.
Scientists have successfully grown organoids with cellular structures similar to those of human brains. However, none of the previous models developed human-like functional neural networks. Networks appear when neurons are mature and become interconnected, and they are essential for most brain activities.
"You can use brain organoids for several things, including understand normal human neurodevelopment, disease modeling, brain evolution, drug screening, and even to inform artificial intelligence," Muotri says.
The team began to detect bursts of brain waves from organoids at about two months. The signals were sparse and had the same frequency, a pattern seen in very immature human brains. As the organoids continued to grow, they produced brain waves at different frequencies, and the signals appeared more regularly. This suggests the organoids have further developed their neural networks.
However, it's not likely these organoids have mental activities, such as consciousness, Muotri says. "The organoid is still a very rudimentary model -- we don't have other brain parts and structures. So these brain waves might not have anything to do with activities in real brains."
"It might be that in the future, we will get something that is really close to the signals in the human brains that control behaviors, thoughts, or memory," Muotri says. "But I don't think we have any evidence right now to say we have any of those."
"As a scientist, I want to get closer and closer to the human brain," Muotri says. "I want to do that because I see the good in it. I can help people with neurological conditions by giving them better treatments and better quality of life. But it's up to us to decide where the limit is. It might be that the technology is not ready yet, or we don't know how to control the technology. This is the same kind of discussion around CRISPR in babies, and that's why we have ethics committees to represent all parts of the society."
Michael Cook is editor of BioEdge
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