2023-06-24 22:27:18
Summary: Researchers have mapped neural activity in the octopus’ visual system, revealing striking similarities with humans. The team observed neural responses to the bright and dark dots, creating a map that resembles the organization of the human brain. Interestingly, octopuses and humans shared the last common ancestor around 500 million years ago, which indicates an independent evolution of these complex visual systems. These discoveries contribute greatly to our understanding of cephalopod vision and brain structure. Highlights: About 70% of an octopus’s brain is dedicated to vision. This research is the first of its kind to map neural activity in their visual system, providing insight into how these marine creatures perceive their world. Despite having a common ancestor 500 million years ago, octopuses and humans evolved similar neural maps for visual perception. The study found that octopus neurons react strongly to small bright spots and large dark spots, which is different from the human visual system. This is likely due to the peculiarities of the underwater environment. Source: University of Oregon Octopuses devote about 70% of their brain to vision. But until recently, scientists had only a vague understanding of how these marine animals see their underwater world. A new study from the University of Oregon sheds light on the octopus’s perspective. For the first time, neuroscientists have recorded the neural activity of an octopus’ visual system. They created a map of the octopus’ visual field by directly observing neural activity in the animal’s brain in response to light and dark spots at different locations. This map of neural activity in an octopus’s visual system is very similar to what we see in a human brain — even though octopuses and humans shared a common ancestor some 500 million years ago, and octopuses evolved their complex nervous systems independently. Neuroscientist Christopher Neale and his team report their findings in an article published June 20 in Current Biology. “No one has really recorded from the central visual system of a cephalopod before,” Neal said. Octopuses and other cephalopods aren’t usually used as models for understanding vision, but Neal’s team is intrigued by their unusual brains. In a related article published last year in Current Biology, the lab identified different classes of neurons in an octopus’ optic lobe, a part of the brain dedicated to vision. “Together, these papers provide a good foundation by showing the different types of neurons and what they respond to — two key aspects that we want to know to start understanding a new visual system,” Neal said. In the new study, the researchers measured how neurons in the octopus’ visual system responded to dark and light spots moving across a screen. Using fluorescence microscopy, the researchers were able to watch the activity of neurons as they responded, to see how neurons reacted differently depending on where the spots appeared. “We can see that each site of the optic lobe responds to a location on the screen in front of the animal,” Neal said. “If we move from one point, the response is transmitted to the brain.” This type of individual maps are found in the human brain for multiple senses, such as vision and touch. Neuroscientists have linked the location of certain sensations to specific points in the brain. A well-known representation of touch is the homunculus, a cartoon human figure in which parts of the body are drawn in proportion to the amount of brain space devoted to processing sensory input. Very sensitive points such as the fingers and toes feel huge because there is a lot of brain input from these parts of the body, while the less sensitive areas are much smaller. But finding an orderly relationship between the visual scene and the octopus brain was far from certain. It’s a rather complex evolutionary innovation, and some animals like reptiles don’t have this kind of map. In addition, previous studies have indicated that octopuses lack a homunculus-like map of different parts of their bodies. “We had hoped that a visual map would exist, but no one has seen it directly before,” Neal said. The researchers also noted that the octopus neurons responded particularly strongly to small bright spots and large dark spots — a marked difference from the human visual system. Neal’s team hypothesizes that this may be due to the specific characteristics of the underwater environment in which the octopuses must navigate. Imminent predators may appear as large dark shadows, while nearby objects such as food may appear as small bright spots. Next, the researchers hope to understand how the octopus’s brain reacts to more complex images, such as those already found in its natural environment. Their ultimate goal is to trace the pathway of these visual inputs deeper into the octopus’ brain, to understand how the octopus sees and interacts with its world. About this research in Visual Neuroscience News Author: Molly BlanchettSource: University of OregonContact: Molly Plancet – University of OregonImage: Image credited to Neuroscience NewsOriginal research: access.”Functional regulation of visual responses in the optic lobe of octopusesby Christopher Neal et al. Current Biology Abstract Functional regulation of visual responses in the optic lobe of octopuses Strengths Functional organization of the visual system of cephalopods is largely unknown Using calcium imaging, we mapped visual responses in the optic lobe of octopuses We identified spatially localized receptive fields with retinal organization The on and off pathways were distinct And they have unique size-selective characteristics Summary Cephalopods are highly visual animals with camera-like eyes, large brains, and a rich repertoire of visually-directed behaviors. However, the brains of cephalopods evolved independently of those of other species with high vision, such as vertebrates. Therefore, the neural circuits that process sensory information are very different. How their uniquely powerful visual system works is largely unknown, as there have been no direct neurological measurements of visual responses in the brains of cephalopods. In this study, we used two-photon calcium imaging to record visually evoked responses in the primary visual processing center of the octopus central brain, the optic lobe, to determine how basic features of the visual scene are represented and organized. We found spatially localized receptive domains of light (ON) and dark (OFF) stimuli, which were retinally organized across the optic lobe, demonstrating a visual system organization feature shared by many species. Examination of these responses revealed shifts in visual representation across layers of the visual lobe, including emergence of the OFF pathway and increased size selectivity. We also identified asymmetries in the spatial processing of on and off stimuli, which suggest unique circuit mechanisms for model processing that may have evolved to meet the specific demands of processing an underwater visual scene. This study provides insights into the neural processing and functional organization of the octopus visual system, highlighting both common and unique aspects, and lays the foundation for future studies of the neural circuits mediating visual processing and behavior in cephalopods.
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