Performing research using these balls of brain cells that grow and form brain-like structures on their own over the course of eight weeks should be superior to studying mice and rats because they are derived from human cells instead of rodents, they said.

"Ninety-five percent of drugs that look promising when tested in animal models fail once they are tested in humans at great expense of time and money," said study leader Thomas Hartung, professor at Johns Hopkins University in US.

Researchers, including Anupama Kumar of John Hopkins University, created the brains using what are known as induced pluripotent stem cells (iPSCs). Cells from the skin of several healthy adults were used to create the mini-brains, but Hartung said that cells from people with certain genetic traits or certain diseases can be used to create brains to study various types of pharmaceuticals.

The brains can be used to study Alzheimer's disease, Parkinson's disease, multiple sclerosis and even autism.

The mini-brains are very small - at 350 micrometres in diameter, or about the size of the eye of a housefly, they are just visible to the human eye - and hundreds to thousands of exact copies can be produced in each batch.

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