Miniature "human brains" have been grown in a lab in a feat scientists hope will transform the understanding of neurological disorders.
The pea-sized structures reached the same level of development as in a nine-week-old foetus, but are incapable of thought.
The study, published in the journal Nature, has already been used to gain insight into rare diseases.
Neuroscientists have described the findings as astounding and fascinating.
The human brain is one of the most complicated structures in the universe.
Scientists at Institute of Molecular Biotechnology of the Austrian Academy of Sciences have now reproduced some of the earliest stages of the organ's development in the laboratory.
Brain bath They used either embryonic stem cells or adult skin cells to produce the part of an embryo that develops into the brain and spinal cord - the neuroectoderm.
This was placed in tiny droplets of gel to give a scaffold for the tissue to grow and was placed into a spinning bioreactor, a nutrient bath that supplies nutrients and oxygen.
A cerebral organoid - the brown pigments are a developing retina
The cells were able to grow and organise themselves into separate regions of the brain, such as the cerebral cortex, the retina, and, rarely, an early hippocampus, which would be heavily involved in memory in a fully developed adult brain.
The researchers are confident that this closely, but far from perfectly, matches brain development in a foetus until the nine week stage.
The tissues reached their maximum size, about 4mm (0.1in), after two months.
The "mini-brains" have survived for nearly a year, but did not grow any larger. There is no blood supply, just brain tissue, so nutrients and oxygen cannot penetrate into the middle of the brain-like structure.
One of the researchers, Dr Juergen Knoblich, said: "What our organoids are good for is to model development of the brain and to study anything that causes a defect in development.
"Ultimately we would like to move towards more common disorders like schizophrenia or autism. They typically manifest themselves only in adults, but it has been shown that the underlying defects occur during the development of the brain."
The technique could also be used to replace mice and rats in drug research as new treatments could be tested on actual brain tissue.
'Mindboggling' Researchers have been able to produce brain cells in the laboratory before, but this is the closest any group has come to building a human brain ( via bbc.co.uk ).