Monday , August 2 2021

A surprising discovery reveals a second visual system


The visual system is probably the best part of the brain. In the past 75 years, neuroscientists have learned a detailed description of how light waves enter into our eyes allow us to recognize the face of our grandmother, to follow the falcon on the fly or to read prayer. But a new study by researchers at the University of California, UC San Francisco, in the United States, examines the fundamental aspect of the science of vision, which shows that even the best studied parts of the brain are still They can contain many surprises.

According to the standard model of visual processing, all visual information of the retina must first pass through the primary visual cortex (V1) in the back of the brain, which extracts simple functions, such as lines and edges, before being distributed to a number of " higher visual areas "that extract more complex features such as shapes, shading, motion, and so on.

The new study, published in Science's Digital Edition on Friday, for the first time shows that one of these supposedly superior visual areas, which is involved in the perception of moving objects, does not depend on information at all. from V1. By contrast, this region, known as the post-cortical cortex (POR), appears to receive visual data directly from evolutionary old sensory centers for brain-based processing called superiors.

"It's like we've discovered a second primary visual cortex," said lead author of the study, Massimo Scanciani, UCSF physiology professor and researcher at the Medical Institute Howard Hughes. "This undermines the whole concept of the visual system in the mammalian cortex as a perfect hierarchy with V1 as a watchdog and raises a multitude of questions, including how these two parallel visual systems developed and how they collaborate to create a unified visual experience." add

Superior superior quantities (called optic tecton in non-mammals) is the main center of sensory processing in small or no-bark creatures, such as fish, amphibians, lizards, and birds. It is particularly adapted to the movement and associated with reflective behaviors: for example, the ability of a frog to catch air with flying with the tongue or the ability of fish to escape from a nasty predator.

However, the superior coliculus does not disappear with the development of the cortex in the mammal. In primates, including people, it is associated with fast and unconscious forms of visual processing, such as jumping out of fear when you see a stick that looks like a snake, or automatically grasping the ball that you throw on your face.

You can also play a role in focusing the focus on visual attention (for example, when we wait for the dashboard to turn green or look at a crowded scene to look for someone with a red and white hat). But in the new article for the first time someone shows that this evolutionary ancient system has dedicated space in the cortex.


The research began when lead author Riccardo Beltramo, a postdoctoral researcher in the Scanziani lab, noticed neuronal responses to the movement of visual stimuli in the POR mouse, which is known to play a role in the perception and memory of the movement spatial

He used a technique called opacity for temporarily silencing activity in V1 with light in the hope of confirming his expectation that POR responses depend on the flow of information through the standard visual hierarchy. But, to his surprise, he discovered that the PSR neurons continued to react to driving stimuli, even without the introduction of V1.

"It was absolutely remarkable," said Beltramo, "we silenced the main visual surface in the cortex and the visual responses in the POR were not affected, it was the first big moment of surprise that told us we were in something completely unexpected."

If the POR's responses to moving objects do not come from V1, asked Beltramo, how did they get there? There must be another path linking the POR with visual information from the retina, he thought. To identify this parallel visual path, Beltramo used specially designed viral injections that denote neurons that are interconnected with each other. This allowed him to show that the POR neurons received two sources of anatomical information: one from V1 and one from the assumed coliculus, each directed to different areas of the thalamus, the central relay station of the brain.

To confirm that the superior coliculus driven the POR's responses to motion, Beltramo used opto-genetics to systematically silence the V1 or the superior coliculus while shooting from the POR. He showed that, unlike deactivation of V1, exclusion of the upper column caused the POR activity to completely disappear. In fact, the superior coliculus seems to be essential for the ability of the POR to track moving objects, something that the researchers found that POR inputs V1 can not do independently.

The study raises fundamental questions about the brain's evolution and its functioning. More research is needed to test whether visual reactions in POR-like areas of the primate's brain, like us, also depend on the contribution of the superior colic, as well as the way in which the V1-operated and colon-activated activity interacts with animal behavior, say the authors.

"We assumed that the POR, previously considered to be a higher visual area, could be a kind of" primary "visual cortex, similar to the bird, reptile, or simple bird cortex, and that it can be dedicated to discovering that something moves in the environment, be it a small, close prey or a great distant predator, "says Beltramo.

"From this perspective, perhaps V1 will add to this information more precise discrimination of the nature of the moving object, such as its exact location or if it is a potentially delicious beetle or potentially lethal scorpion," he adds.

Based on previous studies, recently discovered superior quantities-POR system can also be associated with reactions to fear, spatial attention and navigation, or even facial recognition: all specialties from the temporal cortex region in which it is located. POR.

Findings may also have implications for an intriguing phenomenon called "blind vision" in which people who are blind from damage to V1 can still identify the positions of objects and move through obstacles, even if they can not consciously perceived. Based on primate studies, it is believed that a blind vision depends on superior coliculus, but a new study suggests that it may also include parts of the brain-like bone similar to POR.

"This is one of those discoveries that generate a lot of questions, instead of responding to anyone, because, like many discoveries, he asks questions that no one knew what to do," Scanciany concludes.

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