Stanford bred mice with human brains
Researchers at Stanford built mice whose cortex is 92% human brain tissue grown from stem cells. The human-derived organoid integrated with the mouse nervous system, supporting organized neural activity and behavior.
Anil Seth and Nita Farahany flagged the obvious ethical minefield: are these things conscious? Do they have human-like cognition? The Stanford team was apparently thorough on ethics, but that doesn't answer whether we should be building chimera mice that might suffer in ways we can't even recognize.
An extraordinary @Nature paper has just landed from the lab of @Sergiu_P_Pasca at @Stanford - led by Konstantin Kaganovsky. They have found a way to create "xenocortical mice" which have ~92% of their cortex occupied by a cortical organoid derived from human stem cells. This human-derived cortical graft integrates deeply with the host nervous system, supporting organised neural activity and behaviour. This study is a milestone in synthetic biology and chimera research. It has the potential to generate multiple medical breakthroughs by providing an enhanced biological model of human brain tissue that allows behavioural as well as neural and genetic assays. The Stanford team have been exceptionally thorough and proactive in addressing ethical concerns that comes from this frontier work. But their pioneering work nonetheless raises many open questions: are the xenocortical mice conscious? Do they have any human-like properties of consciousness or cognition? @NitaFarahany and I will be addressing some of these questions in a forthcoming commentary - where we'll also offer an ethically-informed roadmap to guide this important research as it progresses. In this context, "pacing the frontier" really does make sense 😉 Read the Stanford @nature paper here, and buckle up. It's wild. https://www.nature.com/articles/s41586-026-11032-2
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