In previous work, the Stanford team transplanted human neurons into rat brains. The tissue took root and wired into the animals’ brain circuits, but there was too little room for the human tissue to grow very much.

To solve the problem, the researchers genetically engineered mice to stunt the growth of key brain regions, the cerebral cortex and hippocampus. Surprisingly, the mice survived because the remaining parts of the brain took on new roles. While the mice look normal, they are cautious on their feet and more forgetful.

Uh, hmm, I guess since people are into building torment nexi lately this just makes sense. They talk about growing human brains in mice like it’s old hat, and boy howdy we sure are getting better at it!