Yoshiyuki Hayashi

This article investigates a critical yet underexplored structural aspect of consciousness in the context of the practical ethics of neural organoid research: the unity of consciousness. We advocate for the necessity of the unified field, which has garnered substantial support from both philosophical and empirical standpoints, although the debate remains unresolved. We highlight the brainstem as a potential source of the unified conscious field, a structure already under scrutiny in neural organoid research in relation to conditions such as Parkinson’s disease and post-COVID-19 syndromes. We argue that if unity is a necessary feature of consciousness, consciousness is contingent upon a specific biological system without which consciousness cannot arise, thereby narrowing the range of neural organoids of ethical concern. Furthermore, the transplantation of neural organoids into animals has emerged as a practical concern, with ethical implications varying based on the necessity of the unity of consciousness. We argue that transplantation evades a significant ethical dilemma if unity is necessary and if the organoids to be transplanted lack the neural basis for the unified field of consciousness.

In 2008, researchers created human three-dimensional neural tissue – known as the pioneering work of “brain organoids.” In recent years, some researchers have transplanted human brain organoids into animal brains for applicational purposes. With these experiments have come many ethical concerns. It is thus an urgent task to clarify what is ethically permissible and impermissible in brain organoid research. This paper seeks (1) to sort out the ethical issues related to brain organoid research and application and (2) to propose future directions for additional ethical consideration and policy debates in the field. Toward (1), this paper first outlines the current state of brain organoid research, and then briefly responds to previously raised related ethical concerns. Looking next at anticipated scientific developments in brain organoid research, we will discuss (i) ethical issues related to in vitro brain organoids, (ii) ethical issues raised when brain organoids form complexes or have relationships with other entities, and (iii) ethical issues of research ethics and governance. Finally, in pursuit of (2), we propose research policies that are mindful of the ethics of brain organoid research and application and also suggest the need for an international framework for research and application of brain organoids.

This article proposes a methodological schema for engaging in a productive discussion of ethical issues regarding human brain organoids, which are three-dimensional cortical neural tissues created using human pluripotent stem cells. Although moral consideration of HBOs significantly involves the possibility that they have consciousness, there is no widely accepted procedure to determine whether HBOs are conscious. Given that this is the case, it has been argued that we should adopt a precautionary principle about consciousness according to which, if we are not certain whether HBOs have consciousness—and where treating HBOs as not having consciousness may cause harm to them—we should proceed as if they do have consciousness. This article emphasizes a methodological advantage of adopting the precautionary principle: it enables us to sidestep the question of whether HBOs have consciousness and, instead, directly address the question of what kinds of conscious experiences HBOs can have, where the what-kind-question is more tractable than the whether-question. By addressing the what-kind-question, we will be able to examine how much moral consideration HBOs deserve. With this in mind, this article confronts the what-kind-question with the assistance of experimental studies of consciousness and suggests an ethical framework which supports restricting the creation and use of HBOs in bioscience.