Stanford scientists grow human brain tissue in mice lacking cortex and hippocampus

September 16, 2026 at 08:00 PM2 min

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Stanford University researchers genetically engineered mice missing most of their cortex and hippocampus, then transplanted human brain organoids that grew to occupy the vacant space and wire into the animals' nervous systems. The hybrid mice performed better on a maze memory test than mice without the human cells, according to a study published September 16 in Nature. The work offers a new model for studying human neural circuits and brain disease.

Key Facts

The study was published September 16 in the journal Nature.
The genetically modified mice lack most cells of both the cortex and the hippocampus.
Human organoids transplanted into these mice grew to occupy most of the vacant space and wired into the animals' nervous systems.
Mice with human cells performed better on a maze memory test than mice without them.
The work underwent review by independent bioethics panels, according to study co-author Sergiu Pașca.

The Hybrid Model

Stanford University neuroscientist Sergiu Pașca led the team that created the hybrid mice. The mice were genetically engineered so their brains do not fully develop, leaving most of the cortex and hippocampus absent. Human brain organoids—pea-sized clumps of neurons grown from stem cells—were transplanted into the vacant space. Within weeks to months, the human cells divided, grew, and took over most of the available space, eventually dominating the mouse cortex. The human tissue wired into the developing nervous system, forming connections with the mouse brain.

Behavioral Effects

Mice lacking brain tissue appeared fairly normal, walking around and squeaking, but showed memory deficits in a maze test. Mice with transplanted human cells performed better on the maze test, indicating the human tissue contributed to cognition. Pașca calls these animals 'xenocortical mice' and suggests they could be useful for studying brain injuries. The model offers a new way to study human neural circuits and brain disease, according to the researchers.

Research Context and Ethics

In 2022, Pașca and colleagues transplanted human organoids into newborn rats, where human cells made up about one-third of one side of the rat cortex. Rat neurons mature faster than human neurons, limiting how much the human tissue could develop in that model. The new mouse model overcomes that hurdle by providing a larger, slower-developing space for human cells. The work underwent extensive oversight, including review by independent bioethics panels, according to Pașca.