The key to the new 'brain in bottle' research involved nourishing immature cells in a gel-like "matrix" that allowed the complex organoid structures to develop.
These were then transferred to a spinning bioreactor which provided extra nutrients and oxygen, enabling them to grow much larger in size.
After two months of development the "mini-brains" had become globular spheres up to four millimetres in diameter.
Each one surrounded a ventricle-like inner cavity and mimicked the layered structure of a human brain growing within a developing foetus.
The goal of the 'brain in a bottle' was to produce a biological tool that can be used to investigate the workings of the brain, better understand brain diseases, and test out new drugs.
Other experts described the work as "audacious", "exciting" and "stunning".
One predicted the future creation of a simple animal-like brain that could be linked to sense organs and had the ability to learn.
A miniaturised "brain-in-a-bottle" has been grown by stem cell scientists who hope it will lead to new treatments for neurological and mental diseases.
The tiny hollow "organoids", measuring three to four millimetres across, have a structure similar to that of an immature human brain, including defined regions.
But the scientists insist they are still far from the science fiction fantasy of building a working artificial brain - or even replacement parts for damaged brains.
Read: 'Brain in a bottle' grown