The Neuroscience of Octopuses: Why People Think They’re Aliens (And Why They’re Not) 

By Irene Arancio

The idea that octopuses might be aliens emerged from the theory of panspermia (Steele et al., 2018), according to which life on Earth is not entirely of terrestrial origin, and microorganisms may have been “brought” here from space via comets or meteorites. The panspermia theory proposes that these extraterrestrial microorganisms then enabled the rapid and coordinated evolution of animal life during the Cambrian Explosion, whereas animal evolution until that point had been more gradual. Interestingly, one animal in particular is highlighted as a salient example of panspermia: the octopus. 

One may wonder why the authors decided to focus mainly on octopuses, when their theory involves the influence of viruses on several animal lineages. The truth is, there’s no deep scientific reason; it seems to be simply that octopuses feel alien. But why is that?

Intelligence and convergent evolution

“With octopuses, it seems that evolution has managed to create intelligence twice” (Godfrey-Smith,  2016). Granted, this view is a bit sensational, and in reality, there is no single biological definition of intelligence. The best way to visualize this concept is to picture the tree of life: every branch traces our ancestors from more than 600 million years ago, to a simple, worm-like creature with a basic nervous system and no centralized brain (Erwin & Davidson, 2002; Arendt et al., 2008). From this ancestor, multiple evolutionary lineages emerged. Two primary lineages were the vertebrate lineage, which resulted in mammals and birds, and the invertebrate lineage, which led to cephalopods such as octopuses. Starting from that common ancestor, evolution followed completely different paths. 

Octopuses thus developed advanced cognition and a complex brain independently from mammals. This evolution of similar traits in species of different lineages is called convergent evolution (Stayton, 2015). Isn’t it weird to think that from such a simple creature, two completely different lineages emerged that, at some point in time, converged in similar aspects despite their many biological differences? Conspiracy theorists definitely think so, often pointing to it as evidence that octopuses must be alien. Scientists, however, do not see it as “alien” at all, just weird enough to be extremely interesting. 

Otherworldly body appearance

The otherworldly body and appearance of octopuses play a significant role in why they feel alien. Their eight arms can twist, curl and move with hypnotising grace, each one lined with hundreds of suckers that grip and chemically sense the environment. Despite their soft, boneless bodies, they also possess a hard beak that feels oddly out of place for a marine creature (Hunt & Nixon, 1981).

Octopus skin is also full of specialized cells, such as chromatophores, iridophores, and leucophores, that allow them to not only change their colour and brightness but even their texture! These changes are driven by muscular structures called papillae that they can raise or flatten to turn their skin from smooth to bumpy in seconds (Gonzales- Bellido, 2018), enabling octopuses to change their appearance to hunt or hide from predators. 

Yet it is not just their biology that sets them apart, but the extraordinary abilities that emerge from it. Their nervous system is radically different from our own: their doughnut-shaped brain wraps around their esophagus, and around two-thirds of their neurons reside not in their head but in their arms, each capable of processing information and directing movement semi-independently (Chung, Kurniawan & Marshall, 2022). Considering what they can actually do with this unique architecture, it is easy to see why conspiracy theories of octopuses as extraterrestrial persist, and camouflage being the most obvious place to begin. 

Visual information from the eye is first processed in the brain, translated into motor commands, and relayed to the anterior and posterior chromatophore lobes. The chromatophore lobes project to motor neurons distributed throughout the skin. These peripheral motor neurons directly innervate chromatophores, controlling the rapid expansion and contraction of pigment sacs across the arms, mantle and head to match the pattern they are trying to imitate (Dubas et al., 1986; Meijer-Kuiper, 1993). 

What’s more interesting is that while octopuses are able to generate multi-color skin camouflage patterns, their eyes can only detect light and dark, making them effectively color-blind (Messenger, Wilson, & Hedge, 1973).  So how do color-blind octopuses camouflage in a colorful environment? One theory is that octopuses exploit a phenomenon called chromatic aberration (Stubbs and Stubbs, 2016), where different wavelengths of light focus at slightly different distances and create subtle colour-dependent blurring on the retina. If an octopus can detect those tiny differences in focus, it might be able to extract indirect information about wavelength, basically getting “clues” about color without having multiple types of light sensors. 

Another theory is that octopuses rely heavily on brightness rather than color itself. They can detect luminance, so they may regulate their chromatophores based on luminance information from their eyes to match the lightness and contrast of their surroundings. Chromatophores contain only yellow, brown, red, and black pigments and mainly act as brightness regulators: when they expand, more pigment is visible, and the skin appears darker; when they retract, less pigment is exposed, and the skin looks lighter. Beneath these chromatophores, embedded deeper in the skin, are reflective cells called iridophores and leucophores. When chromatophores retract, more light reaches these underlying reflective cells. Unlike chromatophores, they do not contain pigment but instead reflect ambient light.  Leucophores disperse incoming light more widely, producing the appearance of white, but iridophores reflect specific wavelengths, which can result in blues and greens (Packard & Sanders, 1971).  In this way, adjusting chromatophores allows the animal to produce colors that can match background hues. These extraordinary adaptations can make octopuses feel almost alien.

A familiar kind of smart 

Octopuses’ unique brain anatomy allows them to learn from experience, form memories and navigate challenges much like humans do: hallmarks of complex cognition that require adaptation in response to new challenges and planning for future needs. In fact, even though their central brain lacks a cerebral cortex and a hippocampus, the brain regions that in mammals are associated with memory and problem-solving, octopuses are adept learners and problem-solvers. 

For instance, one study found that octopuses were able to solve a multi-step puzzle, while quickly recognizing the need to change strategy when faced with new tasks, demonstrating notable behavioral flexibility (Richter et al., 2016). In another study, octopuses were observed in the wild collecting and transporting coconut shells, later assembling them as protective shelters. Although these shells were not immediately useful, the octopuses transported them for future use, suggesting not only foresight but also advanced problem-solving abilities (Finn, Tregenza & Norman, 2009).  

Interestingly, the octopus brain does not have a cortex. Rather, it has what is called a vertical lobe. This structure is the largest lobe in the octopus’s centralized brain, and it gathers sensory input from the optic lobes. The vertical lobe, along with a network of distributed neurons throughout the body, is known as the vertical lobe system, and is closely tied to learning and memory.

In fact, cephalopods’ vertical lobe functions in ways similar to memory systems in vertebrates. In this area, connections between nerve cells can strengthen with repeated use, a process known as long-term potentiation, which helps learn new information and store memories (Hochner et al., 2003). In simple terms, the more certain neurons “fire” together, the stronger their connection becomes. Recent studies have also shown that this region is organized in a forward-flowing network, meaning information moves through it in a structured sequence (Bidel et al., 2023). This structure may help the octopus process experiences and support complex learning.

The mind of the Octopus

If complex cognitive functions can arise from neural structures radically different from ours, might octopuses possess a form of consciousness? We know they have a brain, but do they possess a mind? 

Unfortunately, we do not yet have an answer to this question. The philosophical topic of octopus consciousness and subjectivity is still widely debated, but if you’d like to explore this idea further, Peter Godfrey-Smith’s book  “Other Minds: The Octopus, the Sea, and the Deep Origins of Consciousness” is a really good starting point. Godfrey-Smith is a philosopher who also happens to spend a lot of time diving with octopuses, and his book argues that evolution may have ‘invented’ minds more than once, and ours might not even be the most interesting version.

Whatever position one takes, the debate over octopus consciousness brings us back to the question at the heart of this article: why do they seem so alien to us in the first place? Octopuses show us that complex cognitive abilities can emerge from brains built very differently from our own. If that is the case, perhaps the deeper issue is not whether they are alien, but whether our existing models of mind are flexible enough to recognize forms of higher-order intellect that evolved so differently from ours. And that leaves us with a final question: what, exactly, is required to have a “mind”?

What would you like to read about next? Let us know here!

~~~

Written by Irene Arancio

Illustrated by Irene Arancio

Edited by Anna Hakimi, Katilyn Huizar, Janie Oberhauser, Dhruv Mehrotra, and Faustina Jayaprakash

~~~

Become a Patron!

References  

Hunt, S., & Nixon, M. (1981). A comparative study of protein composition in the chitin-protein complexes of the beak, pen, sucker disc, radula and oesophageal cuticle of cephalopods. Comparative Biochemistry and Physiology Part B: Comparative Biochemistry, 68(4), 535-546. https://doi.org/10.1016/0305-0491(81)90071-7

Arendt, D., Denes, A. S., Jékely, G., & Tessmar-Raible, K. (2008). The evolution of nervous system  centralization. Philosophical Transactions of the Royal Society B: Biological Sciences, 363(1496), 1523- 1528. https://doi.org/10.1098/rstb.2007.2242  

Erwin, D. H., Davidson, E. H., & New Collective Author (2002). The last common bilaterian ancestor. Development (Cambridge, England), 129(13), 3021-3032. https://doi.org/10.1242/dev.129.13.3021  

Godfrey-Smith, P. (2016). Other minds: The octopus, the sea, and the deep origins of consciousness. Farrar,  Straus and Giroux.

Richter, J. N., Hochner, B., & Kuba, M. J. (2016). Pull or push? Octopuses solve a puzzle problem. PloS  one, 11(3), e0152048. https://doi.org/10.1371/journal.pone.0152048  

Gonzalez-Bellido, P. T., Scaros, A. T., Hanlon, R. T., & Wardill, T. J. (2018). Neural control of dynamic 3-dimensional skin papillae for cuttlefish camouflage. iScience, 1, 24-34. https://doi.org/10.1016/j.isci.2018.01.001 

Steele, E. J., Al-Mufti, S., Augustyn, K. A., Chandrajith, R., Coghlan, J. P., Coulson, S. G., … & Liu, Y.  (2018). Cause of Cambrian explosion-terrestrial or cosmic?. Progress in Biophysics and Molecular  Biology, 136, 3-23.

Stayton C. T. (2015). What does convergent evolution mean? The interpretation of convergence and its implications in the search for limits to evolution. Interface focus, 5(6), 20150039. https://doi.org/10.1098/rsfs.2015.0039 

Hamasaki, D. I. (1968). The ERG-determined spectral sensitivity of the octopus. Vision research, 8(8), 1013-1021.

Stubbs, A. L., & Stubbs, C. W. (2016). Spectral discrimination in color blind animals via chromatic aberration and pupil shape. Proceedings of the National Academy of Sciences of the United States of America, 113(29), 8206–8211. https://doi.org/10.1073/pnas.1524578113 

Meijer-Kuiper, W. (1993). Skin patterning in Octopus vulgaris and its importance for camouflage [Master’s thesis, University of Groningen]. ⁠University of Groningen Research Database. https://fse.studenttheses.ub.rug.nl/9981/  

Dubas, F., Hanlon, R. T., Ferguson, G. P., & Pinsker, H. M. (1986). Localization and stimulation of chromatophore motoneurones in the brain of the squid, Lolliguncula brevis. Journal of Experimental Biology, 121(1), 1-25. https://doi.org/10.1242/jeb.121.1.1 

Messenger, J. B., Wilson, A. P., & Hedge, A. (1973). Some evidence for colour-blindness in Octopus. Journal of Experimental Biology, 59(1), 77-94. https://doi.org/10.1242/jeb.59.1.77 

Chung, W. S., Kurniawan, N. D., & Marshall, N. J. (2022). Comparative brain structure and visual processing in octopus from different habitats. Current Biology, 32(1), 97-110.e4. https://doi.org/10.1016/j.cub.2021.10.070 

Finn, J. K., Tregenza, T., & Norman, M. D. (2009). Defensive tool use in a coconut-carrying octopus. Current biology, 19(23), R1069-R1070. https://doi.org/10.1016/j.cub.2009.10.052 

Bidel, F., Meirovitch, Y., Schalek, R. L., Lu, X., Pavarino, E. C., Yang, F., Peleg, A., Wu, Y., Shomrat, T., Berger, D. R., Shaked, A., Lichtman, J. W., & Hochner, B. (2023). Connectomics of the Octopus vulgaris vertical lobe provides insight into conserved and novel principles of a memory acquisition network. eLife, 12, e84257. https://doi.org/10.7554/eLife.84257 

Hochner, B., Brown, E. R., Langella, M., Shomrat, T., & Fiorito, G. (2003). A learning and memory area in the octopus brain manifests a vertebrate-like long-term potentiation. Journal of Neurophysiology, 90(5), 3547-3554. https://doi.org/10.1152/jn.00645.2003 

Packard, A., & Sanders, G. D. (1971). Body patterns of Octopus vulgaris and maturation of the response to disturbance. Animal Behaviour, 19(4), 780-790. https://doi.org/10.1016/S0003-3472(71)80181-1