Summary: A new map of the octopus’ visual system classifies different types of neurons in a part of the brain dedicated to vision, shedding new light on the evolution of the brain and wider visual systems.
Source: University of Oregon
It’s hard for the octopus to pick just one party trick. He swims by jet propulsion, fires ink chemicals at his enemies, and can change skin in seconds to blend in with his surroundings.
A team of researchers from the University of Oregon is studying another distinguishing characteristic of this eight-armed marine animal: its exceptional visual abilities.
In a new paper, they present a detailed map of the octopus’ visual system, classifying different types of neurons in a part of the brain devoted to vision. The map is a resource for other neuroscientists, giving details that could guide future experiments. And it could also teach us something about the evolution of brains and visual systems more broadly.
The team reports its findings on October 31 to current biology.
Cris Niell’s lab at UO studies vision, primarily in mice. But a few years ago, postdoc Judit Pungor brought a new species to the lab: the California two-spotted octopus.
Although not traditionally used as a subject of study in the laboratory, this cephalopod quickly aroused the interest of neuroscientists at UO. Unlike mice, which aren’t known to have good vision, “octopuses have an incredible visual system and a large part of their brain is dedicated to visual processing,” Niell said. “They have an eye remarkably similar to the human eye, but after that the brain is completely different.
The last common ancestor between octopuses and humans dates back 500 million years, and the species have since evolved in very different contexts. Scientists were therefore unsure whether the parallels in the visual systems extended beyond the eyes, or whether the octopus instead used completely different types of neurons and brain circuits to achieve similar results.
“Seeing how the eye of the octopus convergently evolved in the same way ours did, it’s cool to think about how the octopus’ visual system could be a model for understanding the complexity of the brain of more generally,” said Mea Songco-Casey, a graduate student in Niell’s lab and first author. On paper. “For example, are there fundamental cell types that are necessary for this highly intelligent and complex brain?”
Here, the team used genetic techniques to identify different types of neurons in the octopus’ optic lobe, the part of the brain devoted to vision.
They selected six main classes of neurons, distinguished according to the chemical signals they send. Examining the activity of certain genes in these neurons then revealed other subtypes, providing clues to more specific roles.
In some cases, researchers have identified particular groups of neurons in distinctive spatial arrangements – for example, a ring of neurons around the optic lobe that all signal using a molecule called octopamine. Fruit flies use this molecule, which is similar to adrenaline, to increase visual processing when the fly is active. It could therefore perhaps have a similar role in octopuses.
“Now that we know this very specific cell type exists, we can start to go in and understand what it does,” Niell said.
About a third of the neurons in the data did not appear to be quite fully developed. The octopus brain continues to grow and add new neurons throughout the animal’s life. These immature neurons, not yet integrated into the brain circuits, were the sign of an expanding brain!
However, the map did not reveal sets of neurons clearly transferred from human or other mammalian brains, as the researchers thought.
“On the obvious level, neurons don’t map to each other, they use different neurotransmitters,” Niell said. “But maybe they’re doing the same kinds of calculations, but in a different way.”
To dig deeper, it will also be necessary to better understand the genetics of cephalopods. Because the octopus has not traditionally been used as a laboratory animal, many tools used for precise genetic manipulation in fruit flies or mice do not yet exist for the octopus, said Gabby Coffing, a graduate student. from Andrew Kern’s lab. who worked on the study.
“There are a lot of genes that we don’t have a clue what their function is because we haven’t sequenced the genomes of many cephalopods,” Pungor said. Without genetic data from related species as a point of comparison, it is more difficult to infer the function of particular neurons.
Niell’s team is ready for the challenge. They are now working to map the octopus brain beyond the optic lobe, seeing how some of the genes they focused on in this study appear elsewhere in the brain. They also record from neurons in the optic lobe, to determine how they process the visual scene.
Over time, their research could make these mysterious sea animals a little less obscure — and shed some light on our own evolution, too.
About this Brain Mapping and Visual Neuroscience Research News
Author: Laurel Hammer
Source: University of Oregon
Contact: Laurel Hamers – University of Oregon
Image: Image is credited to Niell Lab
Original research: Free access.
“Cell types and molecular architecture of the Octopus bimaculoides visual system” by Cris Niell et al. Current biology
Summary
See also
Cell types and molecular architecture of the Octopus bimaculoides visual system
Strong points
- scRNA-seq and FISH identified molecular cell types in octopus visual system
- Cell types defined by functional and developmental markers show organization of sublayers
- Immature neurons form transcriptional subgroups that correspond to mature cell types
- This atlas is a basis for the study of visual function and development in cephalopods
Summary
Cephalopods have a remarkable visual system, with a camera-like eye and high-acuity vision which they use for a wide range of sophisticated visual behaviors.
However, the brain of cephalopods is organized radically differently from that of vertebrates and invertebrates, and beyond neuroanatomical descriptions, little is known about the cell types and molecular determinants of their visual system organization. .
Here, we present a comprehensive single-cell molecular atlas of the octopus optic lobe, which is the primary visual processing structure in the cephalopod brain.
We combined single-cell RNA sequencing with RNA fluorescence on the spot hybridization to both identify putative molecular cell types and determine their anatomical and spatial organization in the optic lobe.
Our results reveal six major classes of neuronal cells identified through the use of neurotransmitters/neuropeptides, in addition to non-neuronal and immature neuronal populations.
We find that additional markers divide these neuronal classes into subtypes with distinct anatomical locations, revealing greater diversity and detailed laminar organization in the optic lobe.
We also delineate immature neurons of this continuously growing tissue into subtypes defined by evolutionarily conserved developmental genes, as well as novel genes specific to cephalopods and octopuses.
Together, these findings describe the organizational logic of the octopus visual system, based on functional determinants, laminar identity, and developmental markers/pathways.
The resulting atlas presented here details the “parts list” for the neural circuits used for vision in the octopus, providing a platform for investigations into the development and function of the octopus visual system as well as the evolution visual processing.
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