Brain organoids

A recent development in neurotechnology may lead us to reconsider the neurobiological basis of consciousness. It may also lead us to alter our definition of brain death.

Organoids are artificial tissues produced from pluripotent embryonic stem cells derived from a preimplant blastocyst or induced pluripotent stem. Organoids have been developed for organs such as the brain and heart. Brain organoids are engineered from clusters of neural cells and can be transplanted into animal brains. These forms of neurobiological engineering can help us to gain a better understanding of neurogenesis, neural maturation, and neurodegeneration.

Human brain organoids derived from induced pluripotent stem cells, rather than developing embryos or fetuses, do not appear to raise the same ethical issues that arise from using human embryonic or fetal stem cells for research or therapy for various diseases. They do not generate claims about preconceptual and prenatal moral status. Yet there are two main ethical issues in cerebral organoid research. “The first ethical issue is whether cerebral organoids created in vitro have any kinds of consciousness which should be morally considered, while the second ethical issue relates to how non-human animals with human-like brain functions resulting from the transplantation of human brain organoids should be treated.”

These are related issues, because if the transplantation of organoids into human or nonhuman animals generated consciousness, then this could give them a moral status that they did not have before the transplant. This status may give them a right that could generate an obligation to treat them in certain ways. In the remainder of this section, I focus on organoid research for potential transplantation and integration into human brains.

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egal theorist and philosopher Nita Farahany and coauthors have suggested that advances in this research could produce organisms that may develop sensory and cognitive capacities similar to those in humans. But the cerebral organoids that have been produced to date lack the neural networks necessary for sensory input and motor output and the cognitive capacity to interact with the environment. They lack the connectivity that exists in vivo, and this precludes integration into neural circuits. Transplanting organoids into neural tissue does not guarantee that they will integrate into it, which is necessary for neurogenesis and neurorestoration.

One group of researchers has shown how human stem cell-derived cortical organoids transplanted into the somatosensory cortex of rats could integrate into it. But this has yet to be done in humans. Because of these limitations, the probability of organoids having the type of mental life experienced by humans is very low. Cerebral organoids do not have a thalamus, prefrontal cortex, or other structures that receive and process information from the environment that is necessary for consciousness.

Developmental biologist Madeline Lancaster points out that “without input and output, the neurons may be talking with each other, but that doesn’t necessarily mean anything like human thought.” Christof Koch also doubts that current organoids could develop enough neuronal connectivity and information integration in the brain to reach the threshold at which an organism could be considered conscious. But he admits that more advanced organoids might do this. This will require “further neuroscientific findings … to determine whether cell activity patterns are encoded into meaningful information, although there are also strong moral reasons to further develop differentiation induction and functional assessment techniques in brain organoid research.”

Addressing the issue of the moral status of organoids, philosopher Eliza Goddard and coauthors write, “Concerns about consciousness in human brain organoids may be inflated by a commitment to the specialness of human consciousness with cultural tropes driving the intuition that human brain organoids matter morally. Being composed of human neural cells does not give neural tissue moral status, nor would it be sufficient to justify preventing the use of human brain organoids in research.” Further, “identifying the differences between in vitro and in vivo brains provides good reasons to resist over-emphasizing the ethical concern about human-brain organoid consciousness at this time.” The authors cautiously add, however, that “we should exercise epistemic humility as there are gaps in current knowledge that present challenges for developing defeasible regulations on the use of human brain organoids.”

It is possible that cortical and thalamic organoids produced in vitro could be infused or transplanted and integrate into human brains and reverse damage that was considered irreversible. Although it is not probable at this stage of translational research, it is conceivable that organoids could induce neurogenesis, revitalizing atrophied brain tissue and restoring some degree of brain function. This would involve major practical and ethical problems in conducting the procedure. These would include the risks associated with opening the blood-brain barrier and a potential adverse microglial response from the brain’s immune system. Consent to undergo this infusion would require informing surrogate decision-makers for noncompetent patients of these risks. Researchers would have to ensure that the infused organoids migrated to the regions with the greatest potential for activation and regeneration.

There is also the question of what level of consciousness cortical organoids could generate or restore. This would depend on the extent to which organoids could integrate into neural tissue. Even if they did successfully integrate, it cannot be known whether this is an intervention that a brain-dead patient would have wanted. It is unclear whether surrogates consenting to the infusion of organoids into such a patient to revive them would be in their best interest.

Infusing organoids into a brain without integrated thalamocortical and corticocortical function might restore enough neural networks to restore awareness. This might result in reversing a judgment of higher-brain death. Even if infused organoids did not regenerate the cortical networks necessary to restore awareness, revitalization could restore enough subcortical brain function to question and possibly reverse a declaration of death according to whole-brain criteria. This is very different from CPR or other interventions that restart cardiocirculatory and neurological functions that have not permanently but only temporarily ceased. If human brain organoids could be transplanted and integrated into and revitalize neural cells and tissues, then this could radically alter the status quo on the criteria and timing of declaring brain death. This would require substantial revision or replacement of the UDDA and the DDR with different standards. Indeed, both higher-brain and whole-brain conceptions of death would have to be reconsidered.

Whether brain organoids could reverse brain death and regenerate damaged brains will depend on how the research develops, how it is regulated, and whether it changes how we think about and define death. One cannot assume that this intervention would always be beneficial for its recipients. If organoid infusion restored only minimal and not full consciousness, then it is not clear whether an individual previously declared brain-dead would be better off for it. Those living with brain injuries could be worse off if organoids restored enough brain function for them to be aware of their cognitive impairment but did not resolve it. Like other emerging neurotechnologies, with brain organoids we need to avoid both hype and underestimation regarding their neurobiological potential and the ethical issues they raise.

Excerpted from “Neuroethics: The Implications of Mapping and Changing the Brain,” *by Walter Glannon. Reprinted with permission from the MIT Press. Copyright 2025. *