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By Megan Molteni
Sept. 16, 2026
Science Writer
Megan Molteni
Megan covers the intersection of science and society. How is biomedical research funded? Who benefits? And how do new technologies reflect and shape our values? You can reach Megan on Signal at mmolteni.13.
For the last decade, scientists have been steadily getting better at growing “cerebral organoids,”  miniature, three-dimensional brain-like structures, from human stem cells in the lab. Now, a group from Stanford University has found a way to advance their usefulness for studying brain development and disease — by instead growing them inside mice that have had large parts of their own brains genetically removed. 
Neuroscientists say these “neuro-chimeric” mice, whose brains are half-human — by volume, not by number of neurons — are an important innovation for a field hampered by longstanding challenges in accessing human brain tissue for research. But such models also raise a host of ethical questions that will get thornier the more advanced they become. 
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In a study published Wednesday in Nature, the Stanford team reported finding types of human cells inside the brains of 3-month-old chimeric mouse pups that are very hard to obtain in a dish. They included pyramidal projection neurons that had wound their way into some of the animals’ spinal cords. The scientists also found evidence of specialized, super-sized neurons involved in social cognition only found in large-brain mammals like elephants, whales, and primates, including humans. 
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Megan Molteni
Science Writer
Megan covers the intersection of science and society. How is biomedical research funded? Who benefits? And how do new technologies reflect and shape our values? You can reach Megan on Signal at mmolteni.13.
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