Despite the differences that distinguish humans from one another, our brains are astonishingly similar to one another. Why are brains organized so identically to one another? This resemblance is especially striking in a region called the "temporal lobe". In this part of the brain, there are clusters of neurons that help us to recognize critical visual stimuli, like faces, numbers, or words. These clusters appear in the same brain folds across people. Understanding the origin of this shared brain organization can help us to understand what happens when brain development goes awry, as it does in dyslexia or autism.

It turns out you don't get a cluster of neurons for recognizing just any stimulus. We think these regions develop in response to a lot of experience that begins early in childhood and for objects that look similar to one another and require subtle individuation. So far, scientists have been able to observe brain regions involved in recognizing faces, words, numbers, bodies, tools, and places. There are a few theories that explain why these regions are in the same brain folds across people. However, distinguishing the theory which best describes brain development would require children to learn a new visual stimulus that was different from those other essential stimuli. If we could predict the emerging location of a new brain region, we could potentially identify which theory best explains why the brain develops the way it does.

Getting children to pay attention long enough to learn a new visual stimulus would be difficult. However, we realized that the 1990s had already done all the training for us! In 1996, Nintendo and GameFreak released the game Pokémon alongside the GameBoy, which invited kids on a digital adventure in which they collected hundreds of small, pixelated, animal-like creatures. Many children continued playing Pokémon into adulthood. It turns out that Pokémon is the perfect stimulus to help solve this neuroscientific mystery. Pokémon are small, have very linear features (pixels were large and few in the 90s), are intermediately animate, and they're viewed with central vision. Pokémon were thus very different from faces and places, for example, along these four dimensions. Each of these feature dimensions localizes in the human visual cortex like a gradient. Thus, we can make a unique prediction for where a Pokémon region should appear according to each theory.

To that end, we found 11 individuals who were Pokémon experts: they began playing around the age of 5 and continued playing into their adulthood. We matched these experts with 11 similarly-aged novices. To see if the experience with Pokémon leads to a new brain representation, we used functional magnetic resonance imaging (fMRI). Subjects lie inside of a large magnet that measures blood oxygenation in the brain of each individual while they looked at images of different visual stimuli, including Pokémon. Blood oxygenation correlates strongly with neural activity. Using fMRI, we can thus identify which brain regions may have become specialized for Pokémon compared to other objects.

We found that in the brains of Pokémon experts, a part of the temporal lobe (called the occipito-temporal sulcus) responded more to Pokémon than any other visual stimulus. In novices, this brain region was relatively silent for Pokémon and responded mostly to pictures of animals and words. The retinal eccentricity theory was the only one that accurately predicted that specific brain region where Pokémon's responses appeared. That is because images of Pokémon are usually projected to a small area in the center of our retina. Places, in contrast, are much larger and extend to more peripheral portions of the retina. The difference in the retinal image made by Pokémon, compared to other categories, leads to the unique position of its brain region.

This specificity is possible because different parts of the retina connect to different parts of the visual cortex.

This study suggests that the way we look at the world plays a substantial role in the way that our visual brain develops. Thus, different individuals share these dedicated brain regions, probably because of the same experience during childhood. This powerful observation may help to understand the origins of various developmental deficits of the visual system, like face blindness, dyslexia, and some symptoms of autism. Perhaps atypical viewing patterns during childhood hinder the development of these recognition regions.

Next read: Haptics and Sight in Action: a new way to grasp the human brain by Ivan Camponogara , Robert Volcic

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