Miniature brains have been created in test tubes by stem cell scientists who claim they could help combat inherited neurological disorders.
Several of the tiny hollow structures, which measure 3mm-4mm across, were created as a model to help scientists learn what causes some people to develop neurological disabilities.
Although researchers had previously grown slivers of brain tissue using stem cells, the study was the first to create more complex 3D "organoids" which resemble the brain of a 9-week-old embryo.
Each one mimicked the layered structure of a developing human brain, comprising several defined regions such as a cerebral cortex and a forebrain.
Although they could not develop into a fully functioning brain, due in part to blood supply problems, researchers said the structures could help to reveal the genetic causes of brain disorders.
For example, the team, led by Professor Jurgen Knoblich of Austria's Institute of Molecular Biotechnology, analysed an organoid grown from the stem cells of a patient with microcephaly, where the brain grows to a much smaller size.
They found that a genetic mutation had stopped the brain's stem cells from making copies of themselves at an earlier stage than usual, causing the organ to grow to a smaller size, and the condition could be avoided by replacing the faulty gene.
The organoids could also be used to examine the effects of new drugs instead of carrying out experiments on animals.
Experts described the work, published in the journal Nature, as "audacious", "exciting" and "stunning", but added that it had its limitations.