Human Brain Surrogates Research: The Onrushing Ethical Dilemma.

Human brain research is moving into a dilemma. The best way to understand how the human brain works is to study living human brains in living human beings, but ethical and legal standards make it difficult to do powerful research with actual human beings. So neuroscientists have developed four types of surrogates for living human brains in human bodies: genetically edited non-human animals, human/non-human brain chimeras, human neural organoids, and living ex vivo human brain tissues. These new and rapidly improving models offer the hope of understanding human brain function better. If we make our models "too good," they may themselves deserve some of the kinds of ethical and legal respect that have limited brain research in human beings. This article is an initial effort to outline that dilemma.