Artificially Created Tiny Human Brains Show Signs of Neural Activity

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Artificially Created Tiny Human Brains Show Signs of Neural Activity

"I was very excited to see some of the neurons activated at the same time robustly at first."

By Yasmin Tayag

on June 28, 2019

Filed Under Neuroscience

All human experience is rooted in the brain, but we just 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 researchers developed the brain organoid, an artificially grown, three-dimensional cluster of human neurons that faithfully mimics brain development — 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 behind the new paper 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. That team included first and co-corresponding author Hideya Sakaguchi, Ph.D., a postdoctoral fellow at Kyoto University currently at the Salk Institute.

“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 connections 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.

Their “mini brains” were technically “cerebral organoids,” made from the cells that compose the region of the brain known as the cerebrum. 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 cerebrum.

Then, Sakaguchi and his team pulled out some neurons from the organoids and grew them separately, in hopes that this new culture, called a functional neural network, would last longer than the full mini brain and would be less challenging for visualizing dynamic function. It was in this simpler culture that the team watched the neurons cluster and self-organize, spontaneously creating the structure that would support the synchronized activity. Then, “at last,” says Sakaguchi, “I saw very interesting neural function via imaging.”

“The activity in a dish is still preliminary compared with real brain,” he 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 some people worry that consciousness may arise from them, as “brain-in-a-vat” thought experiments have proposed. If the brain cells we grow develop consciousness, will we be any better than the evil AI overlords in the Matrix, placating living brains trapped in laboratories with virtual reality?

Sakaguchi explains that even though the brain organoids are showing signs of spontaneous activity, they are unlikely to develop consciousness because they lack the ability to be stimulated, unlike living brains attached to a body that senses the world.

“It is very difficult to know they are thinking or feeling,” says Sakaguchi. “But we think cerebral organoids without input and output system will not have consciousness since consciousness require subjective experience.”