– Researchers at the Johns Hopkins Bloomberg School of Public Health are growing tiny replicas of the human brain to help the study of neurological diseases in a trend many hope could lead to better treatments and even cures for some of the most debilitating illnesses.

The Hopkins scientists join a handful of other medical researchers around the country who are culturing so-called “mini-brains” in the lab. It’s a relatively new field of scientific inquiry that could revolutionize how drugs are tested for effectiveness by replacing drug testing on lab animals with testing on human cells.

The scientists reprogrammed the genes of human skin cells to make them like embryonic stem cells, which have the capacity to develop into any kind of tissue. These stem cells were then nurtured to become brain cells. The researchers presented their work recently at the American Association for the Advancement of Science conference.

When fully grown, which takes about eight weeks, the three-dimensional mini-brains measure about 350 micrometers, just visible to the human eye, and look like tiny balls. While the versions aren’t exact replicas of brains, they are made of the same neurons and cells, feature the same structures and act in the same way.

The mini-brains provide a better testing ground for scientists, said lead researcher Dr. Thomas Hartung of the Bloomberg School. Human brains are much more complex than the brains of rats now more typically used in research. About 95 percent of the drugs that look promising when tested in animal models fail when tested in humans, said Hartung, who is also director of the school’s Center for Alternatives to Animal Testing.

Scientists say research on mini-brains could improve understanding of disorders such as Parkinson’s, Alzheimer’s and dementia.