Octopus Arms Have Minds of Their Own

Giant Pacific octopus.

Source: Bill Abbott, via Wikimedia Commons. Distributed under a CC BY-SA 2.0 license.

Octopuses and their relatives, like squid and cuttlefish, stand out from other invertebrates in terms of their cognitive complexity and the range of their behaviors. Despite their evolutionary distance from humans and other vertebrates, these animals can use tools, solve complex puzzles, recognize individual people, and explore objects through play.

They do all this and more with a completely unique nervous system.

Dominic Sivitilli, a graduate student in behavioral neuroscience and astrobiology at the University of Washington in Seattle, has built a new model to represent the flow of information between the octopus’s brain and arms. The model, based on previous research in octopus neuroscience and behavior and new observations collected in the lab, was presented at the 2019 Astrobiology Science Conference last month.

While vertebrates possess a highly centralized nervous system, octopuses instead evolved a distributed nervous system with multiple clusters of neurons called ganglia arranged in a network throughout the body. Of the octopus’s 500 million neurons, around 350 million are found in its eight arms.

The arms can independently touch, taste, and move without input from the brain. Even an arm that has been removed from the body can still perform various basic motions, such as reaching and grasping.

“This allows the octopus to outsource a lot of computational capacity from its brain into its arms, where the suckers serve as an important computational unit,” says Sivitilli. “Each sucker has its own cluster of neurons, or ganglion, that serves as a local sensory and motor integration center. This helps the octopus to process massive amounts of information in parallel.”

Parallel processing allows octopuses to react faster to incoming sensory information and to move and keep track of their position in space. Suckers on the arms can acquire sensory information from the environment, process it, and coordinate with neighboring suckers to initiate action, all without input from the brain.

So while the brain might not know exactly where the arms are in space, the arms know where each other are, and that’s enough to coordinate actions like crawling locomotion. The result is a bottom-up decision mechanism rather than the top-down mechanism typical of vertebrates, says Sivitilli.

Sivitilli is interested in how a distributed nervous system like this works when the octopus is engaged in complex behaviors like hunting, which also requires direction from the brain. He also thinks the octopus represents as alien an intelligence as we can meet on Earth. Understanding the octopus mind could prepare us for meeting intelligent life beyond our planet.

“Other intelligence that’s out there is going to evolve along a completely different evolutionary path from us,” Sivitilli says. “If we look at alternative models here on Earth, like the octopus, it will give us some perspective on the diversity of forms a mind can take.”