In a darkened room in a laboratory in London, a group of students and researchers watch a clump of human brain cells settle into their new home: a living mouse brain. On a computer monitor next to a microscope, the human cells light up in flashes of simultaneous activity. Over time, the cells sprout new connections a few centimeters long, and form networks with each other. It’s captivating viewing for his students, says Vincenzo De Paola, who runs the lab at Imperial College London. “It’s all they want to do. I can’t tear them away,” he says.
De Paola’s system is a specialized type of neural chimaera — an area of research that has expanded immensely in the past five years, sparking a debate about the ethics of blending human and animal brain tissue. Proponents say that such systems are necessary to manipulate live human neurons and are already yielding important insights into health and disease. For example, using neural chimaeras, scientists have found differences in how neurons develop and behave in Down’s syndrome and Alzheimer’s disease.
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But others warn that such chimaeras represent an ethical grey zone, because of the potential to blur the line between humans and other animals, or to recapitulate human-like perception or cognition in an animal.
