Octopus can be said to be the most favored species in the animal world. This magical creature is born to swim quickly through a water jet propeller, fire ink-colored chemicals at its enemies, and can change its skin to blend into its surroundings in seconds. Now, a team of researchers at the University of Oregon (UO) has investigated another unique feature of this eight-armed marine animal: its excellent visual ability.
Fluorescent images of the octopus brain show the location of different types of neurons Credit: Niell Laboratory
They list a detailed map of the octopus visual system in a new scientific paper. In this map, they classify different types of neurons in the part of the brain that is specifically used for vision. This result is a valuable resource for other neuroscientists, providing details that can guide future experiments. In addition, it can give us a broader understanding of the evolution of the brain and visual system.
The team reported their findings today (October 31) in the journal Contemporary Biology.
Cris Niell studied vision in the lab of Ohio University , mainly in mice. But a few years ago, postdoctoral Judit Pungor brought a new species to the lab - the California Double Point Octopus.
Although it was not traditionally used as a research subject in the laboratory, this cephalopod quickly attracted the interest of Ohio University neuroscientists. Unlike mice, mice are not known for having good vision, "octopuses have an amazing visual system, and a large portion of their brains are dedicated to visual processing," Niell said. "Their eyes are very similar to those of humans, but after that, the brain is completely different."
The last common ancestor of octopus and humans was 500 million years ago, and since then, these species have evolved in very different environments. Therefore, scientists do not know whether the similarities of the visual system are beyond the scope of the eyes, or whether the octopus instead uses completely different kinds of neurons and brain circuits to achieve similar results.
"It's cool to see how octopus' eyes evolve similarly to our eyes, thinking about how octopus' visual systems can become models that understand brain complexity more generally," said Mea Songco-Casey, a graduate student in Niell's lab and first author of the paper. "For example, are there basic cell types that are needed for this very clever, complex brain?"
Here, the team uses genetic techniques to identify different types of neurons in the octopus' optic lobe, which is the part of the brain that is specifically used for vision.
They selected six major categories of neurons and distinguished them according to the chemical signals they emit. Observing the activity of certain genes in these neurons and then discovering more subtypes provides clues for more specific roles.
In some cases, scientists have precisely pointed out that specific groups of neurons are in unique spatial arrangements—for example, a circle of neurons around the optic lobes all use a molecule called octamine to signal. fruit fly uses this molecule similar to adrenaline when active to increase visual processing. Therefore, it may have a similar effect in octopus.
"Now we know there is this very special cell type, we can start to enter and figure out what it does, and about one-third of the neurons in the data seem to not fully develop. The brain of the octopus continues to grow and add new neurons in the life cycle of the animal. These immature neurons, which have not been integrated into the brain circuit, are a sign that the brain is in the process of expansion!"
However, the map did not show the group of neurons that were obviously transferred from the brains of humans or other mammals, as the researchers thought. These neurons do not map to each other - they use different neurotransmitters. But maybe they are doing the same kind of calculations, just in different ways.
In-depth mining also requires a better understanding of genetics of cephalopods.Gabby Coffing, a graduate student in Andrew Kern's lab who participated in the study, said that since octopuses have not been traditionally used as experimental animals, many tools for precise genetic manipulation of fruit flies or mice are not yet present in the octopus.
has many genes we don't know what their function is, because we haven't sorted the genomes of many cephalopods. Without genetic data from relevant species as comparison points, it is difficult to infer the function of a specific neuron. The research team is meeting this challenge. They are now working to map outside the optic lobe of the octopus brain to see how some of the genes they focus on in this study emerge elsewhere in the brain. They are also recording neurons in the visual lobe to determine how they handle visual scenes.
Over time, their research may make these mysterious marine animals less mysterious anymore - and also provide a little revelation for our own evolution.
