WASHINGTON: Scientists reported on Thursday they had picked up human-like electrical activity in lab-grown brains for the first time, paving the way to model neurological conditions and answer fundamental questions on how our gray matter develops.

It’s not clear whether the pea-sized brains are conscious: the team behind the breakthrough suspect they’re not because the activity resembles that of preterm babies, but they cannot say for certain, opening up a new ethical dimension to this area of research.

So-called “cerebral organoids” derived from adult stem cells have been around for a decade or so but have never previously developed functional neural networks.

“If you had asked me five years ago ‘Would you think that a brain organoid would ever have a sophisticated network able to generate a brain oscillation?’ I would say no,” said Alysson Muotri, a biologist at the University of California San Diego.

A paper published by Muotri and his colleagues in the journal Cell Press said that two factors were responsible for the breakthrough. The first was a better procedure to grow stem cells, including optimising the culture medium formula. The second was initially surprising, but also intuitive when the researchers thought about it: simply allowing the neurons adequate time to develop, just as babies’ brains develop in the womb.

The team began to detect bursts of brain waves from organoids from about two months. The signals were sparse at first and all at the same frequency, a pattern seen in very immature human brains. But as they grew, they produced waves at different frequencies, and the signals appeared more regularly, suggesting further development of their neural networks.

Researchers then compared the brain wave patterns with those of human brains in early development, by training a machine learning algorithm with the activity recorded from 39 prematurely born babies.

The programme was successful in predicting how many weeks the organoids had been developing in their dishes, suggesting they shared a similar growth trajectory to brains in their natural setting.

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