‘Alien-cortical’ mice: Can human brain cells grow inside animals?

In a laboratory in California, in the United States, mice are scurrying around their cages, as mice do. But inside their brains are millions of working human neurons. Researchers at Stanford University have implanted lab-grown human cells into mice genetically engineered to lack parts of their brains, including the cerebral cortex, the outer region that plays a major role in perception, movement, decision-making and attention.

According to a study published in Nature, these so-called “alien-cortical mice” may offer a new way to study neural circuits and brain disorders such as schizophrenia, cerebral palsy and dementia. Putting human brain tissue inside an animal sounds like something out of Mary Shelley’s Frankenstein, but how “human” are these mice, really? And what have the researchers found?

Researchers genetically modified the mice so they were born and grew without most of the cerebral cortex and the neighbouring hippocampus, which are needed for movement, learning and memory. When the animals were two days old, researchers injected human “organoids” into the empty spaces.