Researchers breed mice with half-human brains to understand mental illnesses

Researchers have created mice with half-human brains to better understand disorders and develop treatments for conditions including schizophrenia, epilepsy, cerebral palsy, intellectual disability and rare forms of dementia, according to research reported by The Guardian on Thursday.

The scientists transplanted lab-grown human brain cells into genetically engineered mice that were born without a cerebral cortex or hippocampus, leaving space for human tissue to grow. The technique allows researchers to take cells from patients, turn them into brain tissue in the laboratory and study how disorders affect human neurons—and how treatments might work.

“We’ve been trying really hard as a community to find therapeutic solutions for these conditions, but the reality is that in psychiatry and neurology we’ve been left behind,” said Sergiu Pasca, the Stanford University professor who led the research.

“The human brain is very complex, but it’s also because the human brain is inaccessible,” he added. “Our goal has been to make aspects of human brain development and function accessible for investigation.”

The work builds on research into neural organoids: lab-grown human brain cells that form tiny structures that mimic some features of real brains. While potentially valuable for medicine, organoids raise ethical questions about consciousness, pain and animal welfare.

Pasca said the research had undergone extensive ethical oversight. Emily Jackson, a professor of law at the London School of Economics, said: “Animal welfare is a really important concern,” and the animals would need close monitoring.

Writing in Nature, Pasca reported that newborn mice received injections containing about 100,000 human brain cells each. The mice lacked around 14 million mouse brain cells and developed about 4 million human ones, which made up roughly half their brains by volume.