Salk Institute creates mice with human brain cells for drug testing

A team of researchers at the Salk Institute announced on Tuesday that they have created a mouse whose cerebral cortex contains human neural cells, and they tracked the animal’s movements in a small arena using multiple cameras and computer analysis. The mouse, born from a blend of mouse and human stem‑cell tissue, roamed the arena while a computer recorded its position and speed, providing the first detailed behavioral readout from a chimeric brain that includes human components.

Scientists have been grafting human brain cells into mouse embryos for more than a decade to study development and disease, but most previous models lacked a functional cortex that could be measured in live animals. The new approach uses human induced pluripotent stem cells that are coaxed into cortical neurons before being injected into mouse embryos at a stage when the brain is forming. By allowing the human cells to integrate with the mouse’s own neural network, the team created a hybrid cortex that can support basic sensory‑motor functions. This matters because it offers a platform to test drugs for conditions such as autism, epilepsy and Alzheimer’s disease in a living system that more closely mimics human brain activity than traditional mouse models.

The researchers say the next steps involve refining the technique to increase the proportion of human cells and to map how these cells connect with mouse circuits. They plan to use the platform to study how human neurons respond to disease‑related genes and to screen potential therapies. Ethical oversight will be crucial as the models become more human‑like, and the team has pledged to work with bioethicists and regulators. If successful, the technology could accelerate the discovery of treatments for neurodegenerative disorders and reduce reliance on less predictive animal tests.