Stanford researchers create human-mouse chimera with human brain tissue

Researchers at Stanford University have developed a human-mouse chimera in which human brain tissue occupies approximately 92% of the animal’s cerebral cortex. According to a study published in Nature, scientists genetically engineered mice to develop without most of their cerebral cortex and hippocampus, reducing their total brain tissue by about 50%.

Laboratory-grown human brain organoids, created from stem cells, were transplanted into the vacant areas of the mice's brains. Over two to three months, the human tissue expanded nearly fivefold. The human neurons integrated into the mouse nervous system, developed organized electrical activity, and extended nerve fibers into the animals' spinal cords.

Behavioral testing indicated that the human tissue influenced the mice's functions. Electrical activity in the human brain tissue was associated with facial movements, and the chimeric mice performed above chance on working-memory tests, whereas mice lacking a cerebral cortex without the transplant failed the same assessments.