U.S. neuroscientists have made a groundbreaking advancement by genetically altering mouse embryos to inhibit the development of their cerebral cortex. After birth, the team transplanted organoids created from human neurons into the area where the cortex would typically form. Remarkably, within a few months, the human tissue expanded nearly fivefold, filling over 90% of the available space. The human neurons not only grew within the mice’s brains but also extended projections into their spinal cords, establishing connections with the animals' nervous systems. During the maturation of the human brain tissue, researchers identified von Economo neurons, which are unique cells linked to social cognition. These neurons are typically found only in humans, great apes, elephants, dolphins, and whales, and until this study, had not been successfully replicated in laboratory settings. Co-author Sergiu Pașca noted, "These animal models provide an exceptional platform to investigate how changes associated with diseases in human brain circuitry appear within an intact nervous system." Current organoids, used to study brain development and dysfunction, lack blood flow and the ability to connect with the rest of the body. The creation of these chimeric mice enables scientists to simulate human-specific disorders and investigate conditions such as epilepsy, schizophrenia, and autism. For instance, when the modified mice experienced oxygen deprivation, they exhibited motor issues akin to those observed in cerebral palsy. This raises an ethical question: should researchers be permitted to conduct experiments on such genetically modified mice?
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