Vasco Grilo🔸 comments on The Conscious Nematode: Exploring Hallmarks of Minimal Phenomenal Consciousness in Caenorhabditis Elegans

[Vasco Grilo🔸]

Thanks for comment, Elijah!

I did not find a free version of Elizabeth’s article Developing Valid Behavioral Indicators of Animal Pain, but I have now read this summary from Gemini, and this related article by Elizabeth. I agree with her that nociception does not necessarily imply sentience, but I do not rule this out. Here are some paragraphs I like from the article “All animals are conscious”: Shifting the null hypothesis in consciousness science by Kristin Andrews which relate to the article from Elizabeth you shared.

Given the determinate development of their nervous systems, 30-some years ago it was taken as given that C. elegans are too simple to learn. However, once researchers turned to examine learning and memory in these tiny animals, they found an incredible amount of flexible behavior and sensitivity to experience. C. elegans have short-term and long-term memory, they can learn through habituation (Rankin et al., 1990), association (Wen et al., 1997), and imprinting (Remy & Hobert, 2005). They pass associative learning tasks using a variety of sensory modalities, including taste, smell, sensitivity to temperature, and sensitivity to oxygen (Ardiel & Rankin, 2010). They also integrate information from different sensory modalities, and respond differently to different levels of intoxicating substances, “support[ing] the view that worms can associate a physiological state with a specific experience” (Rankin, 2004, p. R618). There is also behavioral evidence that C. elegans engage in motivational trade-offs. These worms will flexibly choose to head through a noxious environment to gain access to a nutritious substance when hungry enough (Ghosh et al., 2016)—though Birch and colleagues are not convinced this behavior satisfies the marker of motivational trade-offs because it appears that one reflex is merely inhibiting another (Birch et al., 2021, p. 31).

C. elegans are a model organism for the study of nociceptors, and much of what we now know about the mechanisms of nociception comes from studies on this species (Smith & Lewin, 2009). Behavioral responses to noxious stimuli are modulated by opiates, as demonstrated by a study finding that administration of morphine has a dose-dependent effect on the latency of response to heat (Pryor et al., 2007). And, perhaps surprisingly, when the nerve ring that comprises the C. elegans brain was recently mapped, researchers found that different regions of the brain support different circuits that route sensory information to another location where they are integrated, leading to action (Brittin et al., 2021).

Even if we grant the author’s low confidence in nematodes’ having marker five (motivational trade-offs), current science provides ample confidence that nematodes have markers one (nociceptors), two (integrated brain regions), four (responsiveness to analgesics), and seven (sophisticated associative learning). Given high confidence that nematodes have even three of these markers, the report’s methodology would have us conclude that there is “substantial evidence” of sentience in nematodes.

The presence of pain markers in C. elegans and in other animals presumed to be unconscious has led to a rejection of some of these markers; for example, Elizabeth Irvine concludes that given the assumption that C. elegans are not conscious, the evidence that they possess nociceptors, engage in motivational trade-offs and show associative learning invalidates these three markers, and raise questions about others (Irvine, 2020). Irvine’s worry about a marker’s validity would only be strengthened were we to find evidence of it in a brainless animal, such as the sea sponge Porifera, since brainless animals appear to be even worse candidates for sentience. So let us turn to look at the sea sponge.

From the perspective of the lay observer diving through a reef, sponges themselves do nothing. However, sponges reproduce by creating larvae that swim from the parent and later sink and crawl to find a place to settle and metamorphosize into a new sponge. Our current knowledge of sponge larvae behavior is quite slight. What we do know is that the larvae demonstrate negative phototaxis, and their settlement time is increased by the introduction of substrates such as rubble and biofilm into the environment (Wahab et al., 2011). If it were to turn out that sponges engage in motivational trade-offs between light levels and rubble when it comes to selecting a place to settle, would that finding offer more evidence against motivational trade-offs as a marker, should it offer some evidence that sponges are sentient, or should that data imply neither? According to the sentience report’s methodology, the answer is neither, but such evidence should not lead us to reject the marker of motivational trade-offs, either. Rather, high confidence in the presence of zero to one markers should lead us toward agnosticism about sentience in the species, and high confidence in one marker coupled with good research that fails to find the other seven markers should lead us to conclude that sentience is unlikely. On the sentience report’s approach, and contra Irvine, the markers themselves are not open to being invalidated.

I skimmed the article Disentangling perceptual awareness from nonconscious processing in rhesus monkeys (Macaca mulatta) by Moshe Ben-Haim and others. I liked it, but I believe Kristin’s criticism of defining markers of consciousness applies all the same.

I would like the focus to be on comparisons of expected hedonistic welfare across species and substrates (biological or not) instead of their probabilty of sentience. Relatedly, Rethink Priorities (RP) has a research agenda about interspecies welfare comparisons more broadly (not just under expectationaltotal hedonistic utilitarianism).