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Scientific Frontline: Extended "At a Glance" Summary: Brain Function in Mice vs. Primates
The Core Concept: When an animal moves, its visual system adjusts its neuronal activity to process the changing environmental input, but this adjustment operates on the same mathematical evolutionary principles across both mice and primates despite differing sensory outputs.
Key Distinction/Mechanism: Mice respond to large, coarse patches of a visual scene that fluctuate rapidly with movement, causing significant neuronal changes; primates possess a fovea for processing fine visual details that fluctuate rapidly even at rest, making the brain's adjustment to movement far less pronounced.
Major Frameworks/Components:
- Efficient Coding Hypothesis: A mathematical framework proposing neurons have adapted over evolution to process typical natural environmental patterns using the least possible energy.
- Computational Modeling: The researchers extended the efficient coding framework to simulate neuronal processing in the visual cortex of both moving and stationary animals.
- Peripheral vs. Foveal Processing: Peripheral neurons (similar to those in mice) are strongly modulated by movement, whereas foveal neurons (found in primates) are not.
Branch of Science: Neurobiology, Computational Neuroscience, Evolutionary Biology.
Future Application: Improving computational models for artificial vision systems or advancing our understanding of neurological processing disorders related to motion and perception.
Why It Matters: The research proves that the neuronal differences between mice and primates are not due to differing brain functions, but rather the different types of visual input they process, unifying contradictory observations under one core evolutionary principle.
Seeing and moving are directly linked in the brain. When we stand still, the visual scene barely shifts. When we run, by contrast, the environment rushes past, so that the signals reaching the eye become more variable and change faster. Because animals generate this movement themselves, the change is predictable, and the brain can adjust at the moment movement starts rather than waiting for new visual input.
However, the strength of this neuronal adjustment varies considerably between animal species. When a mouse runs, neuronal activity in its visual system undergoes significant changes. In marmoset monkeys, these effects are much weaker or absent. “This raises the question of whether rodent and primate vision follow different rules,” says Wiktor F. Młynarski, professor of computational neuroscience at LMU’s Faculty of Biology.
Together with Jonathan M. Gant—a doctoral researcher in his group—the neuroscientist recently published a study in the journal Science Advances in which they propose an answer to this question. The visual systems of the two animal groups do, in fact, follow the same basic evolutionary principle of information processing. The differences arise because signals that enter the brain through mouse and primate eyes are not the same.
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Jonathan M. Gant
Photo Credit: © LMU / LC Productions
The Brain Adjusts to Motion
The starting point is the efficient coding hypothesis. This mathematical approach assumes that neurons have adapted to typical patterns of their natural environment over the course of evolution. This allows them to carry the most information for the least energy, such as when processing visual signals.
“We wanted to know how these neuronal patterns change when the animal moves,” says Gant. The two researchers thus extended the efficient coding framework to moving observers. To this end, they filmed natural scenes akin to the visual environment of a mouse while it was standing still and walking, and they analyzed footage from cameras mounted on freely moving mice in the laboratory of Cristopher Niell at the University of Oregon.
The neurons of mice and monkeys do not behave differently because their brains work differently, but because they process different inputs.
To analyze these videos, they simulated neuronal processing in the visual cortex of mice and primates. “Based on the theory, we developed computational models of neurons that represent those inputs most efficiently while stationary and moving,” says Gant.
The theory explains several effects that are known from experimental studies. “During movement, neural responses are stronger, their temporal dynamics change, there are weaker interactions between neighboring neurons, and the neural code becomes more accurate,” says Młynarski.
“Starting from the same theoretical principle, our approach can explain all of these effects,” adds Gant. The visual system adapts its processing to how sensory impressions change through the animal’s movement.
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Professor Wiktor Młynarski
Photo Credit: © LMU / LC Productions
Why Mice Have Stronger Responses
The theory also explains why mice and primates differ. Mouse visual neurons respond to large, coarse patches of a scene, which movement affects strongly. By contrast, neurons in the primate fovea—the high-resolution center of the visual field—handle fine details. Such a high-resolution visual signal already fluctuates rapidly at rest, and movement barely changes it.
“We thus predicted that foveal neurons should not be modulated by movement, while peripheral ones, which resemble mouse neurons, should be,” says Gant. Recently published experiments confirmed this prediction. “Consequently, the neurons of mice and monkeys do not behave differently because their brains work differently, but because they process different inputs.”
According to Młynarski, the study also demonstrates the contribution theoretical neurobiology can make by not only describing but explaining the function of neurons: “Theories of neural computation can unify seemingly contradictory observations under common principles, which, I believe, is one of the key roles of theory in the natural sciences.”
Published in journal: Science Advances
Authors: Jonathan M. Gant, and Wiktor F. MłYnarski
Source/Credit: Ludwig-Maximilians-Universität München
Edited by: Scientific Frontline
Reference Number: ns083126_01