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 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 reproduced some of the earliest stages of the organ's development in the laboratory. Their study is published in the journal Nature.
A BBC science reporter said 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.
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 tissues reached their maximum size, about 4mm, after two months. The BBC reports they have survived for nearly a year, but did not grow any larger.
"What our organoids are good for is to model development of the brain and to study anything that causes a defect in development,'' said Dr Juergen Knoblich.
The technique could also be used to replace mice and rats in drug research as new treatments could be tested on actual brain tissue.