Scientists have successfully grown human mini brains in a laboratory.

The new mini brains could lead to understanding about schizophrenia, autism, and other diseases, as well as lending clues to brain development.

The Austrian researchers grew the mini brains with stem cells. The stem cells created a culture that grew into "cerebral organoids," or mini brains. The diminutive brains consisted of several different distinct brain regions.

This landmark study marks the first time that scientists have managed to replicate the development of brain tissue in three dimensions.

The brain is the most complex known natural structure, and scientists haven't known exactly how it grows. Although the brain starts as simple tissue, it quickly develops in very complex ways.

"This study offers the promise of a major new tool for understanding the causes of major developmental disorders of the brain ... as well as testing possible treatments," said Paul Matthews, a professor of clinical neuroscience at Imperial College London, who was not involved in the study.

The scientists were even able to produce a model of how a rare brain condition called microcephaly develops using the mini brains. This suggests that the organoids could be applied to study other disorders.

Researchers Juergen Knoblich and Madeline Lancaster at Austria's Institute of Molecular Biotechnology and at Britain's Edinburgh University Human Genetics Unit "grew" the mini brains beginning with stem cells that were fed special nutrients.

The cells grew into tissue called neuroectoderm, which all components of the nervous system develop from. The tissue was then put into a scaffold and embedded into a spinning bioreactor, which circulated oxygen and nutrients. They then grew into cerebral organoids.

After about two months, they were around 4 millimeters. While they were still small, they had tissues that were distinct and are similar to the structures of a fully developed human brain.

"This is one of the cases where size doesn't really matter," Knoblich told reporters.

"Our system is not optimized for generation of an entire brain and that was not at all our goal. Our major goal was to analyze the development of human brain (tissue) and generate a model system we can use to transfer knowledge from animal models to a human setting."

And, they say, they have a long way to go.

"Saying you can replicate the workings of the brain with some tissue in a dish in the lab is like inventing the first abacus and saying you can use it to run the latest version of Microsoft Windows - there is a connection there, but we're a long way from that sort of application yet," said Dean Burnett, lecturer in psychiatry at Cardiff University.