Scientific and ethical challenges of brain chimeras converge on an ‘enriched’ approach

Abstract

Transplantation of human brain organoids into nonhuman animals has the potential to advance our molecular understanding of human cognition. Yet hybridized nervous systems raise novel scientific and ethical questions that appear to be oriented toward opposing ends – as models become more sophisticated, ethical concerns become more salient. I posit that scientific and ethical challenges arising from interspecies human brain engraftment may be akin to ‘birds of a feather’ that are more entangled, rather than in tension. The scientific value of engrafted organoids depends on the extent to which they provide insights into human neurobiology, while ethical concerns tend to focus on the wellbeing of engrafted animals. Based on a synthesis of empirical and theoretical evidence from neuroscience and philosophical bioethics, respectively, I argue that scientific and ethical challenges converge on a shared interest in achieving the fullest possible maturation of the host animal. The conditions which are favorable to the wellbeing of animals are also consistent with factors that contribute to the elaboration of neuronal features during development and later behavioral traits. Treating engrafted animals as if they already possess higher moral status may, in fact, be necessary for them to develop the neuronal, cognitive, and behavioral traits that are most relevant to our understanding of the human brain. Studies have shown that enriched environments provide the conditions for neurons to mature, more fully, into neural circuits that contribute to complex behaviors, while supporting the wellbeing and individuation of animals. I conceptualize an ‘enriched’ approach toward research using interspecies brain engraftment and offer a case study examining how enriched environments can be used to study the neurobiology of human speech circuits in grafted animals. The uncertainties posed by interspecies brain engraftment illustrates how joint consideration of scientific and ethical perspectives can reveal convergent pathways for advancing human brain research.