{"id":602802,"date":"2026-09-17T02:54:29","date_gmt":"2026-09-17T02:54:29","guid":{"rendered":"https:\/\/www.newsbeep.com\/nz\/602802\/"},"modified":"2026-09-17T02:54:29","modified_gmt":"2026-09-17T02:54:29","slug":"scientists-grew-human-brain-tissue-inside-mice-and-it-actually-worked","status":"publish","type":"post","link":"https:\/\/www.newsbeep.com\/nz\/602802\/","title":{"rendered":"Scientists Grew Human Brain Tissue Inside Mice and It Actually Worked"},"content":{"rendered":"

\"Side<\/a>Side view of a mouse brain showing nerve fibers from the human graft, labeled in green and red, extending through the surrounding mouse brain tissue in blue. Scale bar: 1 mm. Credit: S. Pa\u0219ca Lab, Stanford University<\/p>\n

A mouse brain is not much larger than a thumbnail. In a new experiment, scientists genetically prevented much of its cerebral cortex and hippocampus from developing, then gave millions of human brain cells room to grow in the vacant space.<\/p>\n

The crazy thing is that the human cells actually survived. What\u2019s more, they expanded until human-derived tissue made up most of the animals\u2019 cortical tissue, connected with the mouse brain and spinal cord, and fired in coordinated waves. <\/p>\n

The point wasn\u2019t to make some weird human-rodent hybrid (which isn\u2019t even possible anyway). Instead, the human brain cells trapped inside the mouse are meant to act as a test bed for studying human neurons inside a functioning nervous system. Mice do not naturally develop many disorders that afflict the human brain, and drugs that look promising in rodents often fail in people.<\/p>\n

\u201cEven drugs that actually make it to clinical trial \u2014 that seem to be working really well in animal models \u2014 fail dramatically in clinic,\u201d Sergiu Pa\u0219ca, a Stanford University neuroscientist who led the research, said at a press conference.<\/p>\n

Making Room for Human Cells<\/p>\n

Electrical activity travelling through human brain tissue in a mouse. Credit: Pa\u0219ca Lab.<\/p>\n

Using genetic engineering, the researchers caused most of the developing rodent neocortex and hippocampus \u2014 regions involved in sensation, memory and higher-order processing \u2014 to disappear. The manipulation was quite extreme, cutting total brain tissue volume by roughly half.<\/p>\n

The team then implanted four small human cortical organoids (clumps of neurons) into newborn mice. The organoids had been grown from human induced pluripotent stem cells, which can be made by reprogramming adult cells such as skin cells.<\/p>\n

All of this solved a timing problem. Human neurons mature much more slowly than mouse neurons. In previous transplant experiments, the mouse brain developed its own circuitry so quickly that the human cells were left with little room or opportunity to grow and make long-distance connections.<\/p>\n

So, the team created room in advance by removing most of the cerebral cortex and hippocampus, leaving a large empty space for the transplanted human organoids. The strategy worked: between two and three months after transplantation, the human tissue grew about 4.7-fold. By three months, it made up about 92 percent of the cortical tissue present in the transplanted mice.<\/p>\n

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This is not the first time human neurons were grown in mouse brains. In 2018, researchers showed<\/a> that human brain organoids could become vascularized inside mouse brains. In 2022, Pa\u0219ca\u2019s group transplanted cortical organoids<\/a> into newborn rats. The tissue matured, received sensory input and influenced behavior, but had to grow alongside an intact host cortex. <\/p>\n

A Working Circuit, but Not a Human Brain Inside a Mouse<\/p>\n

\"Image<\/a>Estimated nerve-fibre pathways in the mouse brain. Dashed white lines mark the boundaries of the xenocortical graft. Credit: S. Pa\u0219ca Lab, Stanford University<\/p>\n

By about five to six months, the human neurons resembled the human cortex in mid-gestation, around the late second trimester. Although they did not form the orderly layers of a normal human cortex, related cell types locally clustered together, and the graft generated cell classes difficult to produce in a dish.<\/p>\n

One of the more striking findings was that the human tissue began producing cell types that mice do not normally have. Researchers spotted a small number of cells resembling von Economo neurons, large nerve cells found in humans and some other big-brained mammals. Some of the human neurons also sent long extensions all the way into the mouse spinal cord.<\/p>\n

And yes, the human neurons worked inside the mouse brain. The transplanted tissue became part of the animals\u2019 nervous system, with the human neurons firing together in coordinated bursts. Some of that activity rose and fell alongside the mice\u2019s facial movements.<\/p>\n

But the human cells didn\u2019t seem to affect the mouse\u2019s behavior too much. Sadly, perhaps, there was no Pinky and the Brain moment. <\/p>\n

The rodents\u2019 movement was broadly normal. The genetically modified mice born without most of their cortex struggled with a simple working-memory maze. Those given human brain tissue did better on that test, suggesting the graft restored some function, but they still performed poorly on a more demanding test of longer-term learning.<\/p>\n

\u201cThere is no indication that what\u2019s being created here are mice that can think like humans, or a human brain in a mouse body,\u201d Sarah Chan, a bioethicist at the University of Edinburgh who was not involved in the study, told the BBC<\/a>.<\/p>\n

Disease Models Meet an Ethical Line<\/p>\n

To see whether these mice could help scientists study brain injury, the researchers briefly deprived them of oxygen, mimicking one kind of stress that can damage the developing brain around birth. The human neurons reacted strongly, and two days later the mice showed subtle changes in the way they walked. That suggests the model could be useful for studying conditions linked to oxygen deprivation, including cerebral palsy.<\/p>\n

There\u2019s still a long way to go, though. The human tissue was still immature and did not organize itself like a normal human cortex, which forms in neat layers. It also lacked many of the cell types and connections found in a fully developed human brain.<\/p>\n

At the same time, if the organoids resemble the developed brain, there may be some serious ethical problems at stake. A May 2026 report from the Nuffield Council on Bioethics<\/a> called for stronger governance as neural organoids become more complex, including updated guidance for experiments that place human neural tissue into animals.<\/p>\n

Nita Farahany, a Duke University bioethicist who served on an external ethics board for the Stanford work, told NPR<\/a> that the team had been \u201cincredibly thoughtful.\u201d Still, she said, \u201cthis brings us into new gray areas for which there are not clear ethical guidelines or norms.\u201d<\/p>\n

For Pa\u0219ca, the scientific promise is equally clear. \u201cHere we have a new model that allows us to actually capture aspects of human brain function in a way that has not been possible before,\u201d he told the BBC.<\/p>\n

The findings were reported in the journal Nature<\/a>.<\/p>\n


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