Vision takes up about 70% of an octopus’s brain. However, scientists have only recently gained a murky understanding of these marine animals’ perceptions of their underwater environment. The octopus’s perspective is brought into focus by a new study from the University of Oregon.
Neuroscientists have recorded neural activity from an octopus’s visual system for the first time. By directly observing neural activity in the octopus’s brain in response to light and dark spots in various locations, they have created a map of the animal’s visual field.
Despite the fact that octopuses and humans last shared a common ancestor some 500 million years ago and that octopuses have evolved their complex nervous systems independently, this map of the neural activity in the octopus visual system looks a lot like what is seen in the human brain.
Christopher Niell, a UO neuroscientist, and his team present their findings in a paper that was published on June 20 in Current Biology.
“We could see that each location in the optic lobe responded to a different location on the screen in front of the animal. If we moved an area, the response in the brain shifted.”
Neuroscientist Cristopher Niell
Niell stated, “Nobody has actually recorded from a cephalopod’s central visual system before.” Despite the fact that octopuses and other cephalopods aren’t typically used as models for understanding vision, Niell’s team is fascinated by the unusual brains of these animals. The lab identified various types of neurons in the octopus optic lobe, the part of the brain that is dedicated to vision, in a related paper that was published last year in Current Biology. Niell stated that these papers, taken as a whole, “provide a nice foundation by elucidating the different types of neurons and what they respond to—two essential aspects we’d want to know to start understanding a novel visual system.”
Researchers measured how the octopus visual system’s neurons responded to dark and light spots moving across a screen in the new study. The researchers were able to observe the activity of neurons as they responded using fluorescent microscopy to observe how neurons reacted differently depending on where the spots appeared.
Niell stated, “We were able to see that each location in the optic lobe responded to a single location on the screen in front of the animal.” On the off chance that we moved a spot over, the reaction moved over in the mind.”
The human brain has this kind of one-to-one mapping for all of our senses, including sight and touch. The location of particular sensations has been linked to specific brain regions by neuroscientists. The homunculus, a cartoon human figure whose body parts are proportional to the amount of brain space devoted to processing sensory input, is a well-known representation of touch. Because these body parts send a lot of signals to the brain, highly sensitive areas like the fingers and toes appear huge, whereas less sensitive areas are much smaller.
However, it was far from a given that the octopus brain and the visual scene could be linked in a systematic manner. It’s a fairly intricate evolutionary development, and some animals, like reptiles, lack such a map. Additionally, previous research had suggested that octopuses do not possess a body map similar to that of a homunculus.
Niell stated, “We hoped that the visual map might be there, but nobody had directly observed it before.”
The researchers found that, in contrast to the human visual system, the octopus neurons also responded strongly to large dark spots and small light spots. This could be because of the particular aspects of the underwater environment that octopuses must navigate, according to Niell’s team’s hypothesis. While close-up objects like food might appear as small, bright spots, looming predators might appear as large, dark shadows.
The next thing the researchers want to know is how the octopus brain reacts to images that are more complicated, like those that it sees in its natural environment. In the end, they want to figure out how the octopus sees and interacts with the world by following the path of these visual inputs deeper into its brain.
More information: Judit R. Pungor et al, Functional organization of visual responses in the octopus optic lobe, Current Biology (2023). DOI: 10.1016/j.cub.2023.05.069
