US scientists create mice with human brain cells

Human skin cells were taken and reprogrammed into brain-like tissue structures called organoids. When these organoids were implanted into the mice's brains, the human cells divided, organized, and integrated into the animal's existing brain circuitry, connecting with the rest of the brain and spinal cord. After approximately six months, these human cells began to resemble and function like the outer layer of the mouse brain.

Behavioral tests conducted on the implanted mice showed they performed comparably to normal mice, with researchers emphasizing that these are not mice that think like humans. The aim is to create a more accurate model for studying complex human brain conditions such as epilepsy, autism, and cerebral palsy, for which current animal models are insufficient. This new approach could potentially lead to more effective treatments for these diseases, which have notoriously low success rates in clinical trials.

However, the development also raises ethical questions. Dr. Sarah Chan, a bioethicist at the University of Edinburgh, noted that the study prompts reflection on what it means to alter animal cognition and how to ensure the welfare of laboratory animals in such experiments. Other neuroscientists, like Dr. Ilary Allodi from St Andrews University, described the work as impressive, highlighting that human-specific cell types formed spontaneously in the implanted mice, effectively keeping the 'human program' within the mouse environment.