Do insects have control over their “pain”?

Tam-Tri Le, Phenikaa University (Hanoi, Vietnam)
https://orcid.org/0000-0003-3384-4827

September 10, 2022

It is commonly believed that bugs do not feel pain. Insects do have nociception – the nervous system’s processes of noxious stimuli that help the body avoid harm. However, pain, as how humans experience it, requires the activation of a pain network integrating nociceptive sensory information, memory, emotion, cognition, and self-awareness. Insect nociception is processed in the mushroom bodies and the central complex but is not integrated into a coordinated pain network like humans [1]. Simple neural circuits can produce adaptive behaviors; thus, insects may not need neuronal investment to have a subjective experience of pain.

A more recent study, however, suggests that insects have descending control – advanced adaptive modulation of nociceptive processes found in vertebrates [2]. Descending control of nociception allows an animal to inhibit or prioritize nociception. For example, an animal suppresses pain perception during combat to focus on fighting and increases nociceptive processing afterward in safer conditions to focus on protecting its injuries.

In one of the experiments in the study, researchers observed that amputation of a leg in a fruit fly (Drosophila melanogaster) activates nocifensive behavior. But such responses are reduced when the fly is hungry. Nociceptive signals are transmitted to the suboesophageal ganglion. Competing stimulus signals, such as attraction to food, are also transmitted to this region. Depending on the processed information, nocifensive behavior can be suppressed by leucokinin neurons descending from the suboesophageal ganglion.


Figure: An example pathway for the putative insect descending nociception controls in the Drosophila melanogaster adult [2] (CC BY 4.0); https://royalsocietypublishing.org/cms/asset/7792aa16-c52f-4d70-9330-e0f6d9580186/rspb20220599f04.gif

The study mentions that insects produce certain neuropeptides that might act as pain suppressors, similar to the functions of opioid peptides in mammals [2]. A former study found that food deprivation reduces responses to noxious heat in fruit flies, regulated by the neuropeptide leucokinin and its receptor [3]. Using CRISPR/Cas9 technology to make leucokinin-expressing neurons and its receptor inoperative, the researchers could inhibit the reduction of the flies’ responses to noxious heat.

Fruit flies also become more sensitive and respond more quickly to heat after repeated heat exposure [2]. The issue of signal processing and decision-making related to nocifensive behavior becomes even more intriguing when considering the collective response phenomenon in social insects. For example, an ant colony may act as a neural network and make adaptive responses of moving away from noxious heat based on collective information (such as colony size) rather than individual signal processing [4].

Whether insects can feel pain or not is still a question. But in light of new scientific evidence, we should also raise questions about the ability to actively and intentionally suppress pain in humans. What really is the strength of will anyway? As an information processing system, the human mind evolved from other less complex systems in the biosphere [5]. Thus, it is highly possible to trace back and find the origins of our human abilities in many other creatures living together with us right now on this planet.

References

[1] Adamo SA. (2019). Is it pain if it does not hurt? On the unlikelihood of insect pain. The Canadian Entomologist, 151(6), 685–695. https://doi.org/10.4039/tce.2019.49

[2] Gibbons M, Sarlak S, Chittka L. (2022). Descending control of nociception in insects? Proceedings of the Royal Society B: Biological Sciences, 289(1978), 20220599. https://doi.org/10.1098/rspb.2022.0599

[3] Ohashi H, Sakai T. (2018). Leucokinin signaling regulates hunger–driven reduction of behavioral responses to noxious heat in Drosophila. Biochemical and Biophysical Research Communications, 499(2), 221–226. https://doi.org/10.1016/j.bbrc.2018.03.132

[4] Le TT. (2022). An ant colony is like a neural network. https://mindsponge.info/posts/35

[5] Vuong QH. (2022). Mindsponge Theory. https://books.google.com/books?id=OSiGEAAAQBAJ