All human experience is rooted in the brain, but we only barely understand how it works. That’s partially because it’s hard to study: Scientists can’t just run experiments on living brains, and experiments on animal brains don’t always translate to humans. That’s why they developed the brain organoid, an artificially grown, three-dimensional cluster of human neurons that faithfully mimics brain development ucture — and, as Japanese scientists reported Wednesday in Cell Stem Cell, the neural activity of a living brain as well.
Neurons in a living brain respond to stimuli by “firing” off electrical impulses, which they use to communicate with one another and with other parts of the body. The scientists, which included first and co-corresponding author Hideya Sakaguchi, Ph.D., a postdoctoral fellow at Kyoto University currently at the Salk Institute, discovered that the brain organoids they grew from scratch in their lab also started to exhibit synchronized activity, just like neurons in an actual brain.
“I was very excited to see some of the neurons activated at the same time robustly at first,” Sakaguchi, who did the first of his experiments in December 2016, tells Inverse. “Neurons first show individual activities, but as they form networks and connection between other neurons, they start to show synchronized activities.”
This, he explains, is the basis of human brain function. But he’s not worried that his organoids are at any risk of becoming conscious.
Why Brain Activity Matters
In 1949, the Canadian neuropsychologist Donald Hebb, Ph.D., introduced the Cell Assembly Hypothesis, which posited that synchronized neural activity was the basis for various brain functions, including memory. In 1992, the authors of a Science report put it more succinctly: “neurons wire together if they fire together.” Using their new technique for measuring brain cell activity, Sakaguchi and his team found that brain organoids do the same, even if they’re grown from scratch in a dish.
The “mini brains” were technically “cerebral organoids,” made from the cells that make up the region of the brain known as the cerebellum. They started out as clusters of stem cells raised in a special medium designed to support brain development, eventually growing into organoids with a similar structure as a real-life cerebellum.
Then, Sakaguchi and his team pulled out some neurons from the organoids and grew them separately, in hopes that the new culture would last longer than the full mini-brain. It was in this simpler second culture that the team watched the neurons cluster and self-organize, spontaneously creating the structure that would support synchronized activity.
“The activity in a dish is still preliminary compared with real brain,” Sakaguchi says, “and I think the activity that we detect might correspond to very early stage of cerebral development in a brain.”
It isn’t, he assures Inverse, evidence that the brain is thinking.
Why Brain Organoids Can’t be Conscious
Growing human brain cells is controversial in part because we don’t know whether consciousness may arise from them, as sci-fi premises like the “brain in a vat” scenario have posited.
“In our study, we created a new functional analysis tool to assess the comprehensive dynamic change of network activity in a detected field, which reflected the activities of over 1,000 cells,” says first and co-corresponding author Hideya Sakaguchi, a postdoctoral fellow at Kyoto University (currently at Salk Institute). “The exciting thing about this study is that we were able to detect dynamic changes in the calcium ion activity and visualize comprehensive cell activities.”