Stanford Scientists Create ‘Xenocortical’ Mice With Human Brain Tissue to Study Devastating Brain Disorders

Stanford University researchers have successfully transplanted lab-grown human brain tissue into genetically engineered mice, creating a new experimental platform scientists say could dramatically expand their ability to study neurological and psychiatric disorders that have long been difficult to research directly in living human brains.

The findings, published online September 16 in the journal Nature, describe an approach the research team calls “xenocortication.” Scientists engineered a strain of mice so that most of their neocortex and hippocampus, the brain regions responsible for higher cognitive functions and memory, never formed during early development. Researchers then transplanted human cortical organoids, self-organizing, three-dimensional clusters of laboratory-grown tissue that resemble specific regions of the developing brain, into the resulting cavity shortly after birth.

Cortical organoids are created by reprogramming human skin cells into induced pluripotent stem cells, which can then be coaxed to differentiate into most of the body’s cell types, including the specialized neurons and support cells found in the brain’s outer cortex. The technique builds on years of prior work by the study’s senior author, Sergiu Pașca, a neuroscientist and stem cell biologist who holds the Kenneth T. Norris Endowed Professorship in Psychiatry and Behavioral Sciences at Stanford and directs the university’s Brain Organogenesis Program.

According to Stanford’s own reporting on the study, the transplanted human tissue did not simply survive inside the mice; it expanded rapidly, eventually accounting for more than 90% of the total cortical tissue volume within the mice’s brains roughly three months after the transplant procedure. The human-derived neurons formed working connections both within the graft itself and with the surrounding mouse nervous system, with axons extending as far as the cervical spinal cord. Researchers also recorded coordinated electrical activity across the transplanted tissue, indicating the human cells were forming functional, organized circuits rather than simply existing as inert tissue.

Pașca described the significance of that integration directly. “In these mice, the human grafts generated a broad diversity of cortical cell types and established functional connections throughout the mouse nervous system,” he said. He was careful to characterize the limits of what the model represents, distinguishing it clearly from popular conceptions of “mini brains” grown in a dish. “They are not miniature brains and do not reproduce the full complexity of the human brain, but they allow us to study human neural cell types and developmental processes that would otherwise be extremely difficult to access,” Pașca said.

Remarkably, researchers found that the transplanted tissue contained detectable numbers of von Economo neurons, a rare and unusual type of nerve cell that had previously only been observed in postmortem human brain tissue and had never before been successfully generated either in laboratory culture or in earlier transplant experiments. Compared with previous cortical organoid transplant approaches, the xenocortical grafts also produced roughly three times more of a specific class of projection neurons that extend connections far beyond their region of origin, a feature researchers say makes the model considerably more representative of actual human cortical development than prior techniques.

Despite the scale of human tissue integration, the engineered mice retained largely normal function. Researchers found that so-called “apallial” mice, those genetically modified to lack most of their neocortex and hippocampus before any transplant occurred, were still able to move around their environment, see, hear and smell. Following the human tissue transplant, xenocortical mice performed on behavioral tests in a manner generally comparable to same-age normal mice by three to six months after surgery, despite carrying a brain composed overwhelmingly of human-derived cortical tissue.

To demonstrate the model’s potential research applications, scientists exposed xenocortical mice to five hours of low-oxygen conditions, designed to mimic aspects of the kind of oxygen deprivation that can occur around birth in human infants. That exposure caused substantial damage to the human-derived cortical tissue specifically, and oxygen-deprived xenocortical mice subsequently showed difficulty maintaining a steady gait and balance, a pattern researchers noted bears resemblance to symptoms seen in children with cerebral palsy. Normal mice and apallial mice lacking the human tissue transplant, by contrast, were largely unaffected by the same low-oxygen exposure. Pașca said understanding that difference could prove scientifically valuable well beyond the immediate experiment. “Finding out what accounts for this difference could yield clues about human neural susceptibility to oxygen deprivation, shed light on mechanisms underlying cerebral palsy and provide a platform for testing potential therapeutic strategies,” he said.

Researchers say the broader platform could eventually help scientists study a range of conditions that have historically been extremely difficult to investigate at the cellular and molecular level in living human brain tissue, including profound autism, schizophrenia, cerebral palsy and epilepsy. Alison Singer, president of the Autism Science Foundation, described the potential significance of the approach for future precision medicine efforts. “The idea that you can make an organoid model with an individual’s unique genetic character and use that to learn what’s gone awry in that individual’s brain is a critical step toward precision medicine,” Singer said.

Given the ethical complexity inherent in transplanting human neural tissue into animal models, Pașca organized a conference in Asilomar, California, in November 2025 specifically to debate the ethical implications of this kind of research before the study’s publication. Stanford’s Office of Technology Licensing holds patents related to the generation of cortical organoids, with Pașca listed as an inventor, along with a separate provisional patent application covering the organoid transplantation technique itself.

Researchers say the xenocortical mouse platform will primarily serve as a tool for studying how disease-associated genetic changes alter human neural development and circuit formation, and for testing whether potential treatments can prevent or reverse those changes, offering scientists a living system in which to study human brain biology that was previously accessible only through limited postmortem tissue samples or simplified laboratory cell cultures.