In 2011, at the Institute of Molecular Biotechnology in Vienna a postdoctoral researcher, Madeline Lancaster, inadvertently brought about the production of a brain organoid from human embryonic stem cells. The brain organoids neuroscientists can now grow consist of several million neurons. In April 2018, Nature published an article on the ethics of experimenting with brain organoids, which the authors describe like so:
Brain organoids can be produced much as other 3D multicellular structures resembling eye, gut, liver, kidney and other human tissues have been built. By adding appropriate signaling factors, aggregates of pluripotent stem cells (which have the ability to develop into any cell type) can differentiate and self-organize into structures that resemble certain regions of the human brain.
There’s debate about exactly how and to what extent these so-called “mini-brains” resemble human brains. Yet, given considerable similarities with respect to their constitution, neural activity, and structure, cerebral organoids can be used as reliable models of human brains, which is advantageous for neuroscientists who have limited access to the human brain as it functions. The promise is that by studying these miniature models of the human brain we can better understand how it functions and how it malfunctions, and why.
Yet, along with their potential to aid neurological research, cerebral organoids prompt a key question with serious ethical implications: Are they conscious?
Assuming they manifest the similar neurophysiological activity as our brain when we are conscious, it seems such neuronal processes in organoids would correspond to consciousness. However, we can confirm when such processes in the human brain correspond to consciousness via reports from the human subjects. But these little archetypes are mute and motionless. If they are conscious, they cannot report it. And it seems possible that cerebral organoids are not conscious despite their similarities with human brains. To use philosopher David Chalmers’s terminology, it’s possible they are “zombie” mini-brains. A zombie, in the parlance of consciousness research, is a physical duplicate of a conscious subject that is nevertheless not conscious.
The rationale for thinking cerebral organoids have the capacity to be conscious is straightforward. We do not yet know which specific neuronal mechanisms correspond to each specific conscious state, but we do know that there are neuronal mechanism that correspond to our conscious states. Neuroscientists often calls these ‘neural correlates of consciousness,’ or NCC for brevity. If we have identified a correlation between a conscious state and its neural correlate, it can be inferred that the conscious state is present based on the presence of the neural correlate. For example, given that specific coalitions of neurons in the fusiform face area of the visual system become coactive when you see a face, it can be reliably predicted that you see a face when the neurons are coactive. Since the conscious experience of seeing the face consistently correlates with the neural activity, the presence of the neural activity suggests the presence of the conscious state. Given the presence of what is an NCC in the human brain in the cerebral organoid there should also be the same corresponding consciousness. That’s the reasoning suggesting organoids are conscious.
Further questions arise, however, when one considers what we know about neural correlates and the conditions met when human subjects are clearly conscious. As a recent article in Frontiers in Systems Neuroscience argues, NCC are physically sufficient for consciousness. If a neural mechanism that’s typically an NCC in the human brain is present, a physical condition is met for consciousness to be present, which is very important. But there are additional metaphysical conditions to consider that are taken for granted in NCC studies.
First, the brains studied are always part of the whole biological organism (i.e. a human or monkey body) to which they belong as a part. Suppose you observed my legs striding forward in a running motion, you could know that the motion corresponds to my mental intention to run. But suppose you removed my legs from my body and somehow they once again stride forward in a running motion. It’s not clear that there would be a corresponding mental intention to run. In the first case it’s clear. In the second case there might be a corresponding mental intention, but maybe not. It’s unclear. The metaphysical difference in the two cases—that is, whether or not the legs are part of the whole organism to which they belong—makes an epistemic difference regarding our ability to infer a corresponding mental intention. The upshot is that whether the entity in question is currently part of the whole to which it belongs makes a difference. In the case of cerebral organoids in a petri dish, they are not part of a biological body like a functioning human brain is.
Second, consciousness is not a free-floating property. Rather it always has a bearer, which is the conscious subject, as the philosopher Mihretu Guta has pointed out in Consciousness and the Ontology of Properties. As thought requires a thinker, experience requires an experiencer. The experiencer is the conscious subject that is in the conscious state of hearing the loud sound or seeing red. In the studies that identify NCC, the subject is undoubtedly present. (The only possible exception is study trials involving unresponsive wakefulness syndrome patients.) After all, at some point in the research process reports from the subjects are required so neuroscientists can know the conscious states of the subjects. Thus prior to our knowledge of the NCC is our knowledge that there is a subject. Yet, in the case of cerebral organoids it’s the opposite. We know about the neural activity, but there is no other basis for us to know whether there’s a subject present that could be the bearer of consciousness.
So while the question of whether these little neural nuggets are conscious easily comes to mind, it raises more fundamental metaphysical questions where answers will be hard won. Nevertheless, the ethical implications and potential benefits require continued rigorous reflection.
Matthew Owen
Matthew Owen (PhD, University of Birmingham) is a faculty member in the philosophy department at Yakima Valley College in Washington State. He is also an affiliate faculty member at the Center for Consciousness Science, University of Michigan. Matthew’s latest book is Measuring the Immeasurable Mind: Where Contemporary Neuroscience Meets the Aristotelian Tradition.
