A cross-section of a mini brain showing different brain regions. (Image credit: Copyright: IMBA/ Madeline A. Lancaster )

Talk about thinking small.

Viennese researchers have built tiny brains from human stem cells - a feat that could change the study of neurological diseases.

The mini brains, which measured about 4 millimeters from front to back, had "discrete" but "interdependent" structures just like real brains, according to a study published Wednesday in the journal Nature. They developed out of heaps of human-skin-cells-turned-stem-cells, known as induced pluripotent stem cells.

Learn more about induced pluripotent stem cells.

The small cerebrums allow for "new insights into the development of human brain disorders," according to the researchers.

"They allow for the testing of therapies against brain defects and other neuronal disorders," author Madeline Lancaster of the Austrian Academy of Sciences' Institute of Molecular Biotechnology said in a statement. "Furthermore, they will enable the analysis of the effects that specific chemicals have on brain development."

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Lancaster and colleagues have already used the brainy technique to study microcephaly - a rare neurological condition in which a person's head is smaller than normal. Skin cells taken from someone with microcephaly grew into smaller mini brains than those taken from someone without the disorder, leading the researchers to suspect that stem cells stop dividing and differentiate prematurely in people with the condition.

"A primary goal in neuroscience is to understand the roots of human neurological disease," the researchers wrote in their study, noting that mouse models of microcephaly have failed to capture features of the human disorder. "Our findings suggest that we can use this in vitro culture system to model aspects of human neurodevelopment and neurological disease and hopefully provide novel insight into the pathogenesis of these disorders."