Penn doctoral student Michael Barnett admits he was “obsessed” with Pokémon as a child, spending hours with Pikachu and the gang. So, as he and former Stanford colleague Jesse Gomez discussed a paper about which brain regions light up when young macaques view letters, cartoons, and Tetris pieces, they had an idea.

“We were joking around and said, ‘Wouldn’t it be funny if we essentially played the role that the monkeys did?’” explains Barnett, a third-year graduate student in Penn’s Psychology Department. But rather than Tetris pieces, they made their stimuli the first-generation Pokémon characters from the game’s original red and blue versions.

“As children we had extensive experience playing Pokémon, hundreds of hours. Everyone played on the same Gameboy device, which has the same screen, and kids’ arms are roughly the same length,” he says. “It was like this unintended but well-controlled experiment.” The kidding turned into a study aimed at answering the question, why are visual regions in the brain anatomically consistent across individuals? In other words, why does looking at a face, for example, activate the same spot in each person’s brain?

In a study of 11 Pokémon experts and 11 novices, Barnett and Gomez found that viewing Pokémon characters stimulates activity in a particular area of the visual cortex, in the bottom of the temporal lobe, just behind the ears. What’s more, the area doesn’t overlap with those activated when viewing similar targets like faces, places, or words. The findings, published in the journal Nature Human Behavior, could help to further explain the brain’s structure.

“This isn’t a definitive study stating that we’ve now uncovered the organizing principles of the entire brain, but it shows that your retina plays a large role in organizing your brain. It speaks to what we’re calling retinal size: How big is the little figure on your retina and what is the fixation pattern?” Barnett says. “As you become an expert with a stimulus, in this case, Pokémon, the average size of that image on the retina may determine where in the brain you’ll develop a specialized region for recognizing it.”

For the study itself, conducted at Stanford University in the laboratory of Kalanit Grill-Spector, the researchers recruited adults who had started playing Pokémon between ages 5 and 8 and who could visually recognize and name all 150 of the original characters. Those experts also had to have continued playing the game into adulthood or revisited it at least once. The control comprised adults who had no experience playing Pokémon.

Participants were asked to name 40 randomly selected Pokémon characters, then in an fMRI machine viewed blocks of images, including objects ranging from faces and bodies to the Pokémon sprites. To avoid false results from someone simply finding Pokémon more interesting than a car or a word, say, the researchers also included cartoon characters like Scooby Doo and Jabberjaw the shark.

Then Barnett and colleagues watched in real-time which brain regions reacted. “There have been a lot of theories about organizational principles of the brain,” he explains. “Once we showed that extensive use of Pokémon allowed for novel selectivity—this little patch that showed up—then we could start to ask what about the stimulus would predict its location.”

Though Barnett’s research focus has since shifted to color perception, he envisions a redo of the Pokémon study in which young children who have never played before get exposure to the game and are then periodically scanned to determine just how much experience results in the Pokémon area of the visual cortex. He could also see a version of the experiment done with another stimulus that kids find fun and rewarding.

For now, however, the Pokémon study—which comes as the game celebrates its 25th anniversary—offers some additional insight into the brain’s inner workings. And, for a brief moment, it sent Barnett and Gomez back in time.

“This was one of those moments that you hear about in science that started as a conversation and became an experiment. Pokémon nowadays does not look like the original Gameboy graphics, so this was a trip down memory lane, and it yielded some interesting results,” says Barnett. “Our message isn’t that video games change your brain. Everything changes your brain.”