Scientists create mice with brains that are half-human
In short: By genetically engineering rodents to lack a cerebral cortex, researchers successfully integrated 3D human brain organoids into living mouse brains. This xenocortication technique allows scientists to observe human neurons developing within an intact nervous system, offering a unique way to study how neurodevelopmental disorders affect behavior and to test new drugs.
This is a significant leap from previous methods where human brain organoids were grown in isolation in a lab dish, which fails to capture how disease or damage affects an animal's behavior. This approach is described as the most extensive integration of its kind ever recorded. It provides a way to test drugs for various developmental conditions.
The process involves reprogramming human skin cells into an immature state to grow organoids that mimic a developing brain. In this specific study, researchers engineered mice to prevent the growth of their own outer brain layer—the cortex—which is vital for attention and decision-making. They then transplanted the human-derived organoids into these gaps. The organoids are typically created from mature human skin cells. These cells are guided to develop into various types of brain cells.
The results are significant: the human tissue successfully extended nerve fibers into the mouse brain. This model provides a unique window into neurodevelopmental disorders like schizophrenia, cerebral palsy, and dementia. Notably, the team even glimpsed a rare human neuron type that had never been successfully grown in a dish before, potentially offering clues to treating specific types of dementia. The study was published in the journal Nature on September 16, 2026. The human tissue was visible as green and red fibers in the mouse brain.
This research builds on a decade of work by the Pașca lab at Stanford University. While previous experiments in 2022 involved transplanting organoids into rats to study Timothy syndrome, those human cells were forced to compete for space with existing rodent tissue. The new xenocortical model ensures the human cells have the space to flourish and integrate properly. The organoids used for the Timothy syndrome study were grown from samples of patients. That research helped identify a potential treatment currently in clinical safety tests.
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Sources
- Summary by Intellect · source: Human Neurons Grew Inside a Living Mouse Brain With Bizarre Results
- Also: Human brain cells transplanted into mice in ‘most extensive’ integration ever
- Also: Scientists Created Mice With Half-Human Brains. The Hybrid Animals Could Revolutionize Our Understanding of Neurological Disorders
- Also: Human neurons flourish in mouse brains, offering a new view of neurodevelopmental disorders
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