Growing stem cells

To create their brain tissue, Juergen Knoblich and Madeline Lancaster at Austria's Institute of Molecular Biotechnology and fellow researchers at Britain's Edinburgh University Human Genetics Unit began with human stem cells and grew them with a special combination of nutrients designed to capitalise on the cells' innate ability to organise into complex organ structures.

They grew tissue called neuroectoderm - the layer of cells in the embryo from which all components of the brain and nervous system develop.

Fragments of this tissue were then embedded in a scaffold and put into a spinning bioreactor - a system that circulates oxygen and nutrients to allow them to grow into cerebral organoids.

After a month, the fragments had organised themselves into primitive structures that could be recognised as developing brain regions such as retina, choroid plexus and cerebral cortex, the researchers explained in a telephone briefing.

At two months, the organoids reached a maximum size of around 4 millimetres (0.16 inches), they said. Although they were very small and still a long way from resembling anything like the detailed structure of a fully developed human brain, they did contain firing neurons and distinct types of neural tissue.

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

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

In an early sign of how such mini brains may be useful for studying disease in the future, Knoblich's team were able to use their organoids to model the development of microcephaly, a rare neurological condition in which patients develop an abnormally small head, and identify what causes it.

Both the research team and other experts acknowledged, however, that the work was a very long way from growing a fully-functioning human brain in a laboratory.

"The human brain is the most complex thing in the known universe and has a frighteningly elaborate number of connections and interactions, both between its numerous subdivisions and the body in general," said Dean Burnett, lecturer in psychiatry at Cardiff University.

"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."