They've finally done it; scientists grew "miniature human brains" in a lab.

The specimens are only the size of a pea and completely void of thought, but it is still an impressive feat, the BBC reported.

A research team at the Molecular Biotechnology of the Austrian Academy of Sciences used stem and skin cells to create a neuroectoderm, the part of an embryo that becomes the brain.

"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 BBC reported.

The cells arranged themselves into the usual brain structure, including: "the cerebral cortex, the retina, and, rarely, an early hippocampus."

The final result was a test-tube brain that had similar development to what would be seen in a nine-week-old fetus.

These tiny brains have been "alive" for almost a year, but have not progressed in development after hitting the nine-week wall.

 "What our organoids are good for is to model development of the brain and to study anything that causes a defect in development," Dr. Juergen Knoblich, one of the researchers, told the BBC.

"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 groundbreaking discovery could also be good news for rodents, which could be replaced in labs by these home-grown organs.

"I think it's just mindboggling. The idea that we can take a cell from a skin and turn it into, even though it's only the size of a pea, is starting to look like a brain and starting to show some of the behaviours of a tiny brain, I think is just extraordinary," Prof Paul Matthews, from Imperial College London, told the BBC.

The mini-brains have already been used to study microcephaly, a human disease that is characterized by a smaller brain.

The Vienna researchers do not see an ethical issue with the current experiments, but worry one would pop up if the specimens became more advanced.

"It's a long way from conscience or awareness or responding to the outside world. There's always the spectre of what the future might hold, but this is primitive territory," Dr. Zameel Cader, a consultant neurologist at the John Radcliffe Hospital in Oxford, told the BBC.