London - Scientists have created laboratory-grown mini-brains which produce similar brainwaves to those of premature babies.
The breakthrough is the closest researchers have come to growing a functioning brain in a petri dish.
The mini-brains begin as human skin cells, which scientists use to create stem cells like those of a baby in the womb – capable of forming any part of the body.
These cells are then grown in a chemical soup which contains the ingredients they need to become brain cells. That has been done before, and the pea-sized "brains" are not the first to be created in the lab, nor are they actual fully operating brains.
But for the first time these mini-organs have been made to "talk" to each other as brain cells do in the human body. When researchers compared their lab-grown brains with those of premature babies, some electrical signals from both were similar.
Just as in growing babies, the mini-brain cells produced a signal which increased in frequency as they got "older".
The mini-organs are likely to be used to study brain development and investigate what goes wrong to cause conditions such as autism and epilepsy.
The researchers face questions about the ethics of their work and say they are cautious not to get too close to recreating a human brain. Their creations have no blood vessels, no brain hemispheres and are not in a skull.
Professor Alysson Muotri, senior author of the study from the University of California, San Diego, said: "It might be that in the future we will get something that is really close to the signals in the human brains that control behaviours, thoughts, or memory.
"But I don’t think we have any evidence right now to say we have any of those."
The mini-organs, also known as brain "organoids", can help to test how drugs might work on the brain.
But to really work properly they have to be grown properly in the right "culture" – the soup of nutrients which mimics conditions in the body to make stem cells differentiate into brain cells.
The study, published in the journal Cell Stem Cell, may have achieved this based on the similarities between some aspects of the mini-brainwaves and EEG readings from pre-term babies.
A computer algorithm was trained to track the electrical signals from the brains of 39 premature babies between six and nine-and-a-half months old, then set loose on the signals from the mini-brains.
The algorithm could predict the age of the brains grown in the laboratory, which were kept for up to ten months, because some brainwaves showed similar maturity and interconnectivity to those of to the growing babies.
Professor Muotri said: "Our work doesn’t yet replace the need for human foetal brain tissue for research, but it’s very attractive as a potential alternative."