“What if intelligent life on Earth evolved not once, but twice?”
– David Van Essen, 2003
Octopuses possess a rich behavioral repertoire1 and the largest nervous systems among invertebrates2. Alongside squids and cuttlefish, octopuses are believed to have evolutionarily separated from humans more than 700 million years ago3. Given that long divergence, we should be a very different species. And we are… in some ways. Octopuses have striking morphological features such as camera-like eyes, an incredibly adaptive coloration system, and eight arms with more suckers than we have fingers or thumbs1, 4.
And yet— they are like us. Even though octopus brains and vertebrate brains have no common anatomy, they both support similar features such as forms of short and long-term memory, versions of sleep, and the abilities to recognize individual people and explore objects through play5. In this post, I will explore cephalopod intelligence and leave you with eight (or more) reasons to be amazed by the octopus.
Thinking in the Deep
In an octopus, the majority of neurons are in the arms themselves— nearly twice as many as in the central brain. Each arm has about 300 suckers and each sucker contains up to 10,000 neurons6. I met with Frank Grasso, a professor of psychology at Brooklyn College, to learn more about the neurobiology of octopuses.
Octopus suckers attach to surfaces as a local reflex. Since chemoreceptors line the sucker rim, the octopus can taste surfaces as it moves. There are also mechanoreceptors and proprioceptors present, which provide information on touch and pressure and muscle activity, respectively.
When contact is detected, the sucker will automatically contract and attach. The mechanoreceptors trigger the reflex to keep what is there from getting away. The taste buds on the sucker rim then more slowly provide information on whether or not the object should be repulsed or retained. In this way, octopuses can ensure that a food item like a crab cannot scour away. It is bad though if an octopus attaches to everything, including itself. Scientists know that this is not the case. An octopus can discriminate between itself and other objects7. How? “We would really like to record the neural activity of the sucker ganglion to know if the signal informing that decision is chemical or mechanical,” Grasso says.
The Incredible Locomotion
With such versatile suckers, octopuses have shown that smart can be spineless. Their arms can maneuver without input from the brain. Even an arm that is surgically removed can reach and grasp objects8. How an octopus coordinates eight such arms in locomotion is still unknown.
Octopuses are indeed masters of distributed control. Grasso and his colleague Michael Kuba have observed that there are two pairs of forward arms that grasp readily and easily. The arms behind are used preferentially for moving the body. “They are hyper-redundant. Whatever the animal wants to do, it could probably do with any of its arms or suckers,” Grasso says.
Hyper-redundancy is what makes octopuses so intriguing to researchers. There’s redundancy in the sensors of the suckers, information processing in the brain, and body structure. The strong yet flexible hyper-redundant arms of the octopus endow it with high maneuverability but also place a great burden on its control system9. It must interface incoming sensory information with the issuing of motor commands. Since the octopus arm does not have fixed joints or fixed linkages, it has infinite degrees of freedom. In other words, each arm has virtually unlimited ways to achieve the same goal with no constraints. How does the octopus actually achieve control over a system that is soft and has hyper-redundancy?
To answer such a question, imaging technologies in the octopus must advance. Grasso jokingly remarked that “you can put a coarse electrode into an octopus arm, and another arm will reach out and rip it out.” His colleague Binyamin Hochner, a professor of neurobiology at the Hebrew University of Jerusalem, has made heroic efforts in this field10. Alternatively, the Grasso lab builds bio-mimetic robots and computer simulations to test their ideas about how control in a hyper-redundant system works.
The Role of Computation
It is undoubtedly difficult to build a soft robot with the mechanical properties of an octopus arm. Arriving at that degree of soft manipulator form and the complexity of an octopus is dually challenging. The Grasso lab instead creates simulations in silica of what an appendage or sucker would be like. The first step is to look to biology to characterize movement. The next step is to build a model that captures what biology is doing. To do so, the Grasso lab uses neural networks inspired by octopus neuroanatomy. There are sensory inputs, motor outputs, and interneurons that model what the nervous system should do. In other words, the neural networks connect sensing in the world to outputs of the world. “We’re testing how the structure of the nervous system and the information that flows through it realizes behavior input,” he says.
Octopuses exhibit such immense intelligence yet live for only one to two years. For Grasso, the short lifespan of the octopus demanded that it be able to learn because there were no ways to genetically program enough behaviors into it to deal with the unexpected nature of its environment. In this way, it isn’t surprising that they learn. It’s completely expected that they would do so to compensate for the world that they live in.
Learning is a process that transforms the structure of an organism to adapt it better to its environment. We learn by exchanging information through language. By participating in a culture, we gain the knowledge of previous generations. In sharp contrast to this, octopuses are solitary creatures. If an octopus had the capacity to take advantage of inherited knowledge, they may very well become our rivals.
- Hanlon, R. T., & Messenger, J. B. (1998). Cephalopod behaviour. Cambridge University Press.
- Young, J. Z. (1971). Anatomy of the Nervous System of Octopus vulgaris.
- Albertin, C. B., Simakov, O., Mitros, T., Wang, Z. Y., Pungor, J. R., Edsinger-Gonzales, E., & Rokhsar, D. S. (2015). The octopus genome and the evolution of cephalopod neural and morphological novelties. Nature, 524(7564), 220-224.
- Wells, M. J.Octopus: Physiology and Behaviour of an Advanced Invertebrate (Chapman and Hall, 1978)
- Godfrey-Smith, P. (2016). Other minds: The Octopus, the sea, and the deep origins of consciousness. Farrar, Straus and Giroux.
- Grasso, F. W. (2010). Sensational sucker. Scientific American, 303(4), 78.
- Crook, R. J., & Walters, E. T. (2014). Neuroethology: self-recognition helps octopuses avoid entanglement. Current Biology, 24(11), R520-R521.
- Harmon, K. (2013, August 27). Even Severed Octopus Arms Have Smart Moves [Blog post].
- Levy, G., & Hochner, B. (2017). Embodied Organization of Octopus vulgaris Morphology, Vision, and Locomotion. Frontiers in physiology, 8.
- Matzner, H., Gutfreund, Y., & Hochner, B. (2000). Neuromuscular system of the flexible arm of the octopus: physiological characterization. Journal of neurophysiology, 83(3), 1315-1328.
Featured Image: Biomimetic Robot by Laboratory of Frank Grasso, Courtesy of Rosa Bartoletti