The Conscious Nematode: Exploring Hallmarks of Minimal Phenomenal Consciousness in Caenorhabditis Elegans

By Vasco Grilo🔸 @ 2025-12-05T17:35 (+30)

This is a linkpost to https://pmc.ncbi.nlm.nih.gov/articles/PMC10723751/

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 on 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.