This is a linkpost for The Conscious Nematode: Exploring Hallmarks of Minimal Phenomenal Consciousness in Caenorhabditis Elegans by Diego Becerra, Andrea Calixto, and Patricio Orio, which was originally published in the International Journal of Psychological Research in October 2023. Below are the abstract, summary of the evidence for consciousness in Caenorhabditis (C.) elegans, and my quick thoughts.
Abstract
While subcellular components of cognition and affectivity that involve the interaction between experience, environment, and physiology -such as learning, trauma, or emotion- are being identified, the physical mechanisms of phenomenal consciousness remain more elusive. We are interested in exploring whether ancient, simpler organisms such as nematodes have minimal consciousness. Is there something that feels like to be a worm? Or are worms blind machines? ‘Simpler’ models allow us to simultaneously extract data from multiple levels such as slow and fast neural dynamics, structural connectivity, molecular dynamics, behavior, decision making, etc., and thus, to test predictions of the current frameworks in dispute. In the present critical review, we summarize the current models of consciousness in order to reassess in light of the new evidence whether Caenorhabditis elegans, a nematode with a nervous system composed of 302 neurons, has minimal consciousness. We also suggest empirical paths to further advance consciousness research using C. elegans.
Summary of the evidence for consciousness in Caenorhabditis elegans
Table 1. Summary of the Current Evidence of the Criteria Reviewed in the Literature for Experiencing (Phenomenal Consciousness) in C. Elegans.
| Criteria | Found in C. elegans | References |
| Differentiated states and global activity | Yes. C. elegans forward and backward gaits are generated by either a reflex chain, or one or more CPG’s [central pattern generators]. Also, pirouettes and other motor commands require reverberating collective nested neural dynamics. Finally, it is argued that C. elegans have true sleep states, and its behavior changes globally under some anesthetics. | Wen et al., 2012; Olivares et al., 2018; Kato et al., 2015; Kaplan et al., 2020; Trojanowski & Raizen, 2016; Nichols et al., 2017; Nambyiah & Brown, 2021 |
| Binding and integration | Yes. There is evidence for multisensory (chemical, mechanical and thermal) integration. Also, several sensory neurons in C. elegans are polymodal. Finally, a computational model of C. elegans’ neural activity show positive values of Phi (ϕ) [see integrated information theory] | Ghosh et al., 2017; Metaxakis et al., 2018; Goodman & Sengupta, 2019; Antonopoulos et al., 2016 |
| Flexible evaluative system | Perhaps. C. elegans is capable of non-associative and associative learning, and of integrating cues with opposing value in order to make a decision. There is some evidence of experience-dependent preferences, gustatory plasticity, and second order learning. | Ardiel & Rankin, 2010; Ghosh et al., 2017; Guillermin et al., 2017; Dekkers et al., 2021; Merritt et al., 2019 |
| Embodiment and self | Perhaps. There is an efferent copy of motor commands. Communication with bacteria promotes intergenerational memories depending on the bacterium’s virulence. Induction of diapause is pheromone-dependent and thus, C. elegans can recognize its community. | Ji et al., 2021; Palominos et al., 2017; Gabaldon & Calixto, 2019 |
| Intentionality | Not known. Mapping of worldly objects or C. elegans’ own body in neuronal networks seems limited, and goaloriented behavior doesn’t seem to be informed by internal states decoupled from the immediate environment. | |
| Selective attention | Not known. |
My quick thoughts
I think further research on the sentience of nematodes would be useful. This is one of the “Four Investigation Priorities” mentioned in section 13.4 of chapter 13 of the book The Edge of Sentience by Jonathan Birch. However, I believe investigating the (expected hedonistic) welfare per animal-year of nematodes and other soil animals conditional on sentience is a much higher priority. I am much more uncertain about it than the probability of sentience. I would not be surprised if I changed my view that one should optimise for increasing the welfare of soil animals and maybe microorganisms. Meanwhile, I continue to recommend research informing how to increase the welfare of soil animals.
Small drive-by question for you: In your opinion, if C. Elegans is conscious and has some moral significance, and suppose we could hypothetically train artificial neural networks to simulate a C. Elegans, would the resulting simulation have moral significance?
If so, what other consequences flow from this—do image recognition networks running on my phone have moral significance? Do LLMs? Are we already torturing billions of digital minds?
If not, what special sauce does C. Elegans have that an artificial neural network does not? (If you’re not sure, where do you think it might lie?)
(Asking out of genuine curiosity—haven’t had a lot of time to interface with this stuff)
Thanks for the questions, Huw!
I would say the moral significance, which for me is the expected hedonistic welfare per unit time, of the simulation would tend to that of the C. Elegans as more components of this were accurately simulated. I do not think perfectly simulating the behaviour is enough for the moral significance of the simulation to match that of the C. Elegans. I believe simulating some of the underlying mechanisms that produced the behaviour may also be relevant, as Anil Seth discussed on The 80,000 Hours Podcast.
Consciousness does not necessarily imply valenced (positive or negative) subjective experiences (sentience), which is what I care about (I strongly endorse hedonism). C. Elegans being conscious with 100 % probability would update me towards them having a greater probability of being sentient, but not that much. I am mostly uncertain about their expected hedonistic welfare per unit time conditional on sentience, not about their probability of sentience. I would say everything, including a Planck volume in deep space vacuum, could have a probability of sentience of more than, for example, 1 % if it is operationalised in a very inclusive way. However, more inclusive operationalisations of sentience will lead to a smaller expected hedonistic welfare per unit time conditional on sentience. So I would like discussions of moral significance to focus on the expected hedonistic welfare per unit time instead of just the probability of sentience, or just the expected hedonistic welfare per unit time conditional on sentience.
I think increasing the welfare of soil animals will remain much more cost-effective than increasing digital welfare. Assuming digital welfare per FLOP is equal to the welfare per FLOP of a fully healthy human, I calculate the price-performance of digital system has to surpass 2.23*10^27 FLOP/$ for increasing digital welfare to be more cost-effective than increasing the welfare of soil animals, which corresponds to doubling more than 29.0 times starting from the highest one on 9 November 2023. One would need 60.9 years for this to happen for Epoch AI’s doubling time of the FP32 price-performance of machine learning (ML) hardware from 2006 to 2023 of 2.1 years.