A deep examination of the octopus’s eyes by neuroscientists
Researchers want to know how the octopus‘s visual system differs from the brain organization of humans and other vertebrates. Their findings might provide light on how visual systems have changed across different species.
The extraordinary visual talents of this eight-armed marine mammal are being studied by a group of experts from the University of Oregon. In a recent study, they describe a comprehensive map of the octopus’ visual system by categorizing various types of neurons in a section of the brain responsible for vision.
Other neuroscientists can use the map as a resource because it contains information that might direct future research. Additionally, it may help us understand how brains and visual systems have evolved more generally.
The Institute of Neuroscience’s Associate Professor Cris Niell’s lab mostly uses mice to study vision. The California two-spot octopus, however, was a new species that Judit Pungor, a postdoctoral researcher, introduced to the lab a few years ago.
Despite not being a common lab study subject, cephalopods rapidly piqued the curiosity of UO neuroscientists. According to Niell, octopuses have an exceptional visual system, and a significant portion of their brain is devoted to visual processing, in contrast to mice, which are not recognized for having good vision. They have an eye that is strikingly similar to the human eye, but their brains are entirely different from ours.
Since their last shared ancestor 500 million years ago, humans and octopuses have evolved in vastly different environments. Therefore, it was unclear to scientists whether the octopus used similar visual processes to those of the eyes or whether it used entirely different types of neurons and brain circuits.
Mea Songco-Casey, a graduate student in Niell’s lab and the paper’s first author, said that given how similarly the octopus eye convergently developed to ours, it’s intriguing to consider how the octopus visual system can serve as a model for comprehending brain complexity more generally. For instance, are there basic cell kinds needed for this extremely complex, intelligent brain?
In this case, the team employed genetic methods to distinguish between several types of neurons in the octopus’ optic lobe, the area of the brain responsible for vision.
Using the chemical signals that neurons send as a basis for differentiation, they identified six major kinds of neurons. Then, other subtypes were identified in those neurons based on the activity of particular genes, offering hints of more specialized tasks.
The researchers were able to identify specific groups of neurons in some instances that were arranged in discrete spatial configurations, such as a ring of neurons surrounding the optic lobe that all communicate via the octopamine signaling chemical. This substance, which is akin to adrenaline, is used by fruit flies to speed up visual processing while the fly is active. So it might play a similar function in octopuses.
We can begin to investigate and ascertain what it does now that we are aware of the existence of this very particular cell type, Niell added.
The research showed that about a third of the neurons didn’t appear to be properly formed. Throughout the octopus’s lifetime, the brain continues to develop and add new neurons. These developing neurons were a marker of the developing brain because they had not yet been incorporated into brain circuits.
The map, contrary to the researchers’ expectations, did not show any clusters of neurons that were clearly derived from human or other mammalian brains.
The neurons are utilizing various neurotransmitters, thus it is clear that they do not map onto one another, according to Niell. But perhaps they are performing the same calculations in a different manner.
Gaining more knowledge about cephalopod genetics will also be necessary to go deeper. According to Gabby Coffing, a graduate student in biology professor Andrew Kern’s lab who worked on the project, many of the techniques that are used for precise genetic manipulation in fruit flies or mice don’t yet exist for the octopus because it hasn’t historically been utilized as a lab animal.
Because we haven’t sequenced the genomes of many cephalopods, Pungor added, “there are many genes whose function we don’t know what it is.” It is more difficult to determine the purpose of specific neurons when there are no genetic data from closely similar species to compare with.
The team of Niell is up for the task. They are currently mapping the rest of the octopus brain to determine if any of the genes they focused on in this study are present elsewhere in the brain. In order to learn how the optic lobe neurons interpret the visual scene, they are also recording from these neurons.
