Emotional Pain Experience In Invertebrates

When a noxious stimulus is sensed by your neurons, a specific signal enters your central nervous system. For example, contacting boiling water may result in you indeliberately jumping or jerking your arm away. This process is called nociception which is a simple reflex response (Treede et al., 1999). On the other hand, pain is thought to require a very complex nervous system. It is an emotional state including suffering and distress. Almost all vertebrates are known to experience pain. However, pain in invertebrates is not discussed much (King et al., 2009).

Briefly, invertebrates are animals without a bony skeleton or a backbone. Their sizes range from microscopic mites and insects to meters-long squids. Almost all of these creatures have alien-like shapes and features that make them genuinely suitable for horror movies. Photographer Thomas P. Peschak must have thought so to come up with his ‘’Crabzilla’’ project.

However weird or fascinating invertebrates might look, various research and studies caused scientists to settle with the notion that the presence of a backbone is the defining characteristic of a complex mind. Since these animals do not have one, they must be dull. Aiming to challenge this notion, Robyn J. Crook conducted an experiment on octopuses.

She introduced a Bock’s pygmy octopus to two chambers: one with stripes on the walls and the other with spots. These patterns were intended to catch its attention and for it to remember the patterns. A day was given for the octopus to linger between the two chambers and to explore. The following day, she took the octopus out of the chambers and injected acetic acid into one of its arms and placed it into the chamber in which it lingered the most (the one it initially preferred). The octopus woke up with a stinging pain in its arm. 20 minutes later, she removed it from the chambers once more to inject lidocaine into its arm to make the arm numb and placed it into the chamber which it initially did not prefer. Once more, after 20 minutes, she removed the octopus from the chambers and placed it into another tank. In the last step, she placed the octopus back into the chambers after five hours. Now the octopus was presented with a decision: to return back to the initially preferred chamber where it woke up with a stinging arm, or to the initially non-preferred chamber where it woke up with a numb arm. The tested octopuses always returned back to the initially non-preferred chamber.

In order to make the results valid, she observed seven other octopuses with saline injected into their arm instead of acetic acid (saline did not cause any pain). This was her control group. These octopuses always chose the initially preferred chamber

Altogether, these results indicate that there are complex, conscious processes happening in an octopus’s brain. Octopuses can experience emotional pain. Crook shares, ‘’Octopuses were able to learn to avoid a visually specific location that was explicitly unlinked both in time and space from the injection procedure that initiated nociceptor activation.’’ And thus, the study provides the first example of emotional pain experienced by an invertebrate. Although how this process of pain experience evolved in invertebrates is yet to be discovered, this experiment is groundbreaking in terms of understanding invertebrate behavior and biology.

Works Cited

Harlan, Becky. “How a Photographer Turned a Coconut Crab Into ‘Crabzilla’.” Photography, National Geographic, 3 May 2021, www.nationalgeographic.com/photography/article/capturing-crabzilla.

Treede, R.D., Kenshalo, D.R., Gracely, R.H., and Jones, A.K.P. (1999). The cortical representation of pain. Pain 79, 105–111.

Crook, Robyn J. “Behavioral and Neurophysiological Evidence Suggests Affective Pain Experience in Octopus.” IScience. Elsevier, 23 Feb. 2021. Web. 17 May 2021.

King, T., Vera-Portocarrero, L., Gutierrez, T., Vanderah, T.W., Dussor, G., Lai, J., Fields, H.L., and Porreca, F. (2009). Unmasking the tonic- aversive state in neuropathic pain. Nat. Neurosci. 12, 1364–1366.