As in larger brains, mouse visual cortex neurons with the same function cluster in columns
For over 50 years, it has been known that in the cerebral cortex of many mammals, neurons with the same function are grouped into columns. Now, for the first time, researchers at the Max Planck Institute for Biological Intelligence have been able to demonstrate these structures in the visual cortex of mice: here, neurons that process stimuli from the same eye form clusters. This adds to our general understanding of the structural organization of the brain - and may help to solve the mystery of the columnsˈ function.
3D section of the visual cortex in the mouse. Neurons that process information from one eye are arranged in columns (red) running from the top to the bottom layer of the cortex. The 'red' columns are surrounded by neurons processing information from the other eye (blue). For a long time, it was assumed that such structures did not exist in the mouse visual cortex.
© MPI for Biological Intelligence/ Pieter Goltstein
Motion, color, light and shadow: everything we see is the result of complex computations in our brain - or, more precisely, in the visual cortex. This is where stimuli that hit our retina are broken down into their individual components, processed and assembled into what we perceive. The neurons responsible for this process can each perform different tasks: for example, some mainly process motion, others lines or colors.
In the 1960s, David Hubel and Torsten Wiesel famously discovered that in the visual cortex, neurons with the same function are organized spatially in columns. This finding, along with their other discoveries about visual processing, was awarded the Nobel Prize in Physiology or Medicine in 1981. These so-called cortical columns have been considered elementary building blocks in the cerebral cortex of many mammals - including humans. However, such structures had not yet been detected in the visual cortex of many smaller animals, such as mice. As a result, cortical columns were thought to be reserved for mammals with more complex brains and particularly good eyesight.
Visual information coming from the same eye
A team led by Mark Hübener and Tobias Bonhoeffer has now shown for the first time that neurons are also arranged in columns in the visual cortex of mice. Using a technique called 2-photon microscopy, they discovered clusters of neurons that process visual information coming from the same eye. These clusters were most distinct in the middle layers of the visual cortex. However, the spatial proximity of cells processing input from the same eye continued in the overlying and underlying layers, thereby forming so-called ocular dominance columns.
Although the columnar organization of the cerebral cortex was described more than half a century ago, the function of these columns is still a matter of speculation. "A possible explanation for the cortical columns can be illustrated by where fans sit on the stands in a football stadium," says Pieter Goltstein, the study's first author. "If all the fans of one team are sitting together and cheering for their team at the same time, it is much more powerful than if the fans are spread out all over the stadium. It is possible that neurons with the same function can also work more efficiently when they are close together."
The new study not only advances our general understanding of how the brain is organized. It also makes it possible to study the function of the cortical column in the mouse model organism - to perhaps ultimately answer the question what columns are good for.
