Scientists discover brainwaves resembling humans in laboratory-developed mini-brains



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Cross section of a cerebral organoid.
Image: Trujillo et al., 2019, Cell strain cell

Scientists can study the human brain in a non-invasive way by developing "mini-brains", groups of pea-sized brain cells, each in the laboratory. In a fascinating progression of this line of research, a team reported this week that it had observed brain waves resembling those of humans from these organelles.

Previous studies on the mini-brains have demonstrated movement and development of the nervous system, but the new study of researchers from the University of California at San Diego, led by biologist Alysson Muotri, is the first to record a neuronal activity similar to that of a human. In their article, published in Cell strain cell On Thursday, the researchers wrote that they had observed brain wave patterns resembling those of a developing human being. This sophistication in the in vitro The model is a step allowing scientists to use mini-brains to study brain development, model diseases and learn about the brain's evolution, according to Muotri.

"We are good [at studying] cancer, we are good [at studying] heart, "Muotri told Gizmodo by phone," but the brain has fallen behind. "

To create these mini-brains, technically called organoids, the researchers used human pluripotent stem cells and presented them to a nutrient-rich petri dish designed to mimic the environment in which our own brains develop. Due to the pluripotent nature of stem cells (which means that they have the potential to become different cells), these cells could be prompted to develop a 3D structure reminiscent of that of a developing human brain, although that much smaller. After about two months of development, the team began to notice peaks of neural activity on the network that had not been observed before.

Brain organelles, ten months old, each one the size of a pea.
Photo: Trujillo et al., 2019, Cell strain cell

When the team began to observe these intermittent bursts of electrical activity, she was not looking for similarities between her model and that of the child, said Gizmodo, co-author and doctoral student, email.

"We have seen that one of the important characteristics of these organoid oscillations is that they occur in a burst: the network is inactive most of the time and every 10 or 20 seconds or so, an activity would occur spontaneously." said Gao. "This recalled a characteristic in premature babies, called discontinuous trace, where the electroencephalogram was very inactive most of the time, punctuated by strong oscillatory transients. So, if you had to call it a specific feature, I guess it would be the fact that the oscillations come and go … We were really lucky at that time to find a dataset reporting these characteristics in the GET of the premature newborn.

The team formed an automatic learning algorithm to recognize the main characteristics of premature EEGs and asked them to evaluate the similarities between brain organoids. The algorithm was able to predict how many weeks the organoids had grown in the culture and, between 25 and 40 weeks of development of this organoid, it could no longer differentiate between organoids and infantile EEGs, said Muotri to Gizmodo .

But, Muotri said, this comparison between the two was not necessarily one-to-one. There are certain characteristics and limitations of premature EEGs, including the effects of the thickness of a developing human skull on readings, which differ from those of organoids grown in the laboratory. As part of their study, Muotri said the team had left out these non-comparable variables.

The researchers say that, to really consolidate these results, these discrepancies will have to be reconciled between infantile EEGs and organoids.

"I think it's not possible to say how much the activity of organoids is similar to that of premature EEG," explained Arnold Kriegstein, neurologist at the University of Toronto. University of California at San Francisco, who did not contribute to the new study, in an e-mail. "The development of spontaneous activity in organoids is very interesting and the researchers convincingly demonstrated that it depended on neuronal activity. But organelles are so different from the current developing cortex that, even though phenomenology is similar, we still need better evidence that the underlying mechanisms are the same …. It's like comparing apples to oranges: even though they are both fruits, they are not the same. "

Nevertheless, Kriegstein says this research is an important step in answering these questions.

Another issue that this and similar experience raises, said Muotri, is whether the mini-brains can be considered as conscious and what ethical dilemmas could ensue in the future. Kriegstein claimed that organelles were not developed enough to be considered conscious, but Muotri said he could not be sure.

"My initial response was to say" I do not think so, "but the truth is we have no proof anyway," Muotri told Gizmodo. "We do not have any methods to test that yet."

To address this issue, Muotri plans to hold a meeting at the University of San Diego next October with scientists, philosophers and ethicists to discuss the ethical future of these technologies.

"My tendency is always to say, as with any other technology, to take blood transfusions or organ transplants, or even ordinary cars," Muotri said. "These are all technologies that can be used for good and bad, but as a society we see good and bad … and I think brain organoids will go in the same direction."


Sarah Wells is a Boston-based freelance writer who writes about the intersection of technology, science, and society. Follow her on Twitter: @saraheswells.

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