Mini Brains in Petri Dishes

By Maria Lagakos, Contributing Writer

If you’ve ever been in any philosophy course or partaken in a late night existential crisis with your best friend, you may have come across the problem of whether or not an isolated human brain in a jar could possibly have a mind. Although such questions may be coined as far-fetched or belonging to the realm of science fiction, what if I told you that scientists were working on this? While their current aim is not exactly debunking consciousness, neuroscientists are indeed engineering what are called “cerebral organoids” in petri dishes in laboratories across the world.

What exactly are these cerebral organoids? 

Now, my initial sentence may have been slightly misleading. Scientists are not at the brink of creating a whole human brain, or anything near the size or complexity of it. Rather, in the past couple decades scientists have succeeded in growing cerebral organoids: small assemblages of neuronal cells created using human induced pluripotent stem cells (hiPSC). To date, some of the organoids have grown to about 4mm in size (Figure 1) (7). Of course,  growth is still undergoing in laboratories across the world and we have yet to see how this amalgamation of neurons continues to develop. 

Figure 1. Cerebral organoids in a petri dish (Cepelewicz, 2020)

Induced pluripotent stem cells are revolutionary in the biology world. A “pluripotent” stem cell has the capability to develop into any sort of cell. However, an induced pluripotent stem cell is one that is produced from somatic cells – any cell in the body other than sperm or egg cells. The iPSCs act as a blank canvas that can be specifically treated to become any sort of specialized cell in the body. In the case of cerebral organoids, induced pluripotent stem cells are treated to become neural progenitor cells (NPCs), which are the neural cells seen during embryonic development that later develop into neural and glial cells that make up the nervous systems of the body! To date, organoids seem to accurately recapitulate the organization and diversity of certain cell types as well as gene expression during early development (7). That said, cerebral organoids remain complex. Further information regarding the methodologies can be found in various sources (See Figure 2) (1, 7). 

Figure 2. Generation of cerebral organoids (Rabeling & Goolam, 2022)

Because of their ability to similarly replicate development of humans, these organoids have been sought out to study the very beginning of human development. Currently, studying the development of the fetus in embryo is challenging. Furthermore, human development is extremely complex and varied across  individuals. It is precisely the heterogeneity of human developmental pathways – the minute differences that occur between our bodies as they develop –  that makes us, us! Due to this, such initiatives may lead scientists to better understand various developmental pathways, including those atypical pathways  in various neurodevelopmental disorders.

How are scientists using these organoids for clinical purposes?

The causes of neurodevelopmental disorders are commonly studied, yet with limited evidence due to the complexity of retrieving fetal data and ethical implications. For instance, 2D cell cultures and animal models do not provide accurate representations of what occurs in the human brain. Thus, these organoids are hoped to provide more solid ground for understanding pathogenetic development in humans. For example, they have been considered for studying autism spectrum disorder, which is generally characterized as a heterogeneous set of “social and communication deficits caused by numerous genetic lesions affecting brain development” (1). Organoids replicate qualities of the brain during development, such as the formation of areas showing similar cell types and growth as the forebrain, hindbrain and telencephalon in the human brain. Notably, the development of this telencephalon resembling region is of interest to researchers studying autism spectrum disorder, since there is a significant increase in volume in this area in 59% of diagnosed children. It is possible that organoids expressing increased volume in this area may help to understand how this abnormal development occurs (1). Furthermore, Chan et al (2020) also mention that in cerebral organoids grown from iPSCs of individuals with an ASD diagnosis, certain qualities hypothesized to occur in brain development due to specific genes do also appear in the organoids themselves. That being said, they equally note that organoids provide a more accurate depiction of early development and seem to develop differences with prolonged culture. Thus, they suggest that these organoids may be most useful for early neurodevelopmental milestones (3). 

Although most commonly used to study neurodevelopmental disorders, cerebral organoids have been used to study the development of brain tumors. Bian et al. (2018) present in how they instill brain tumor growth within an organoid using CRISPR-Cas9-mediated mutagenesis. To do this, they identified genetic combinations that generated tumors,  then used these to reproduce the process in the cerebral organoid (2). Finally, such models of human development may also provide methods to further understand the evolutionary differences  between human species and some of their closest relatives. For example, in a study conducted by Pollen et al. (2019), the team generated pluripotent stem cell-derived cerebral organoids from chimpanzees in order to identify the point at which the human brain and chimpanzee brain develop differently, and how this differs in terms of genetic expression (4).

It is clearly an exciting time for evolutionary and developmental science, however, such experiments come with challenges. What are some challenges that organoids present to researchers?

The current challenges primarily relate to the substantial differences between cerebral organoids and in vivo development. While future studies may aim to replicate the embryonic environment, at the moment it cannot be said that cerebral organoids truly replicate human development. Additionally, due to the recency of such a method, the protocols and methodology for organoid growth differ across laboratories (3). The lack of agreement and communication raises ethical concerns: organoids don’t belong to a clear category of research, such as human or animal research, making it difficult for ethics committees to reinforce  existing rules about brain organoid studies (6). 

Current organoids have not reached the capacity for sentience and consciousness as we know it, primarily due to the lack of an appropriate environment and sensory input (6). That being said, these organoids are still growing, and methods to improve realistic models of human development continuously emerge. A large part of this field will be dedicated to replicate the conditions of the brain for clinical purposes. This implies ideas such as integrating “networks of functional blood vessels,” even attempting to transplant them into  rats (6). More than this, it seems as though some “have been grown that respond to light, they have been connected with muscle, and they have even been taught to play the simple video game Pong” (5). Thus, it seems plausible to imagine the future of this research conjuring some ethical debates about whether or not consciousness or sentience could arise. Notably, the classic philosophical and ethical concerns regarding how to even define or identify consciousness would clearly be at the forefront of such discussions (5). If we can’t even seem to agree on the definition of consciousness in organisms, such as humans and nonhuman animals, how could we possibly come to the conclusion that the brain organoid may acquire such capacities? Many claim that a key component of our subjective experience comes from our interaction with the world, inputting and outputting data. Is it conceivable for an organoid, hooked up to the world via muscle and sensory organs, to generate consciousness? This remains a topic to explore. 

References:

1. Goolam M. & Rabeling A. (2022, July 5). Cerebral organoids as an in vitro model to study autism spectrum disorders. Gene Therapy. https://www.nature.com/articles/s41434-022-00356-z 
2. Knoblich J. et al. (2018, July 23).Genetically engineered cerebral organoids model brain tumor formation. Nature Methods. https://www.nature.com/articles/s41592-018-0070-7 
3. Mason J. et al. (2020, July 13). Cerebral organoids as tools to identify the developmental roots of autism. Molecular Autism. https://molecularautism.biomedcentral.com/articles/10.1186/s13229-020-00360-3?elqTrackId=1dc892378fbe40869ed6e10e25461d8b 
4. Pollen A. et al. (2019, February 7). Establishing Cerebral Organoids as Models of Human-Specific Brain Evolution. Cell Press. https://www.sciencedirect.com/science/article/pii/S0092867419300509?via%3Dihub 
5. Gardar A. et al. (2023, May 10). Ethical Issues in Cerebral Organoid Research. Cambridge Quaterly of Healthcare Ethics. https://www.cambridge.org/core/journals/cambridge-quarterly-of-healthcare-ethics/article/ethical-issues-in-cerebral-organoid-research/F7B94103FFA7C73CA004F8C29FE32A6D 
6. Cepelewicz J. (2020, January 23). An Ethical Future for Brain Organoids Takes Shape. Quanta Magazine. https://www.quantamagazine.org/an-ethical-future-for-brain-organoids-takes-shape-20200123/ 
7. Ming G. et al. (2019, April 16). Brain organoids: advances, applications and challenges. Development. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6503989/ 
8. Ball P. (2023, June 13). ‘Embryo Models’ Challenge Legal, Ethical and Biological Concepts. Quanta Magazine. https://www.quantamagazine.org/embryo-models-challenge-legal-ethical-and-biological-concepts-20230613/#:~:text=But%20we%20know%20disturbingly%20little,which%20they%20must%20be%20terminated. 

Further resources:

• Harvard Brain Science Initiative. (2021, October 1). Brain Organoids 101.https://youtu.be/8Mk5sYE8ixE?si=ooYZvNNbfMZVTQmZ 
• PHIL306: Philosophy of Mind 
• NSCI300: Neuroethics