Imagine seeing something that isn’t actually there—a trick of the mind that blurs the line between reality and illusion. But here’s where it gets controversial: scientists have discovered a specific group of neurons that might be behind this phenomenon, and they’re not as rare as we once thought. In a groundbreaking study published in Nature Neuroscience (2025), Shin and colleagues reveal that these cells aren’t just oddities—they’re a well-defined, functionally crucial subpopulation in the brain’s visual system.
The team’s findings shed light on how these neurons contribute to pattern completion within the primary visual cortex, a process believed to underlie the perception of illusory contours—those phantom edges our brains create to fill in the gaps. “What’s surprising is that these neurons are directly involved in driving this process,” explains Shin. Adesnik adds, “We’ve shown that these cells play a causal role in pattern completion, which is likely tied to how we perceive illusory contours.”
And this is the part most people miss: while the study demonstrates that artificially activating these neurons can mimic the neural activity seen during normal perception of illusory contours, it doesn’t prove the mice actually saw these illusions. “We didn’t measure behavior in this study,” Adesnik clarifies. “Our focus was on understanding the neural representation.” Shin admits, “It’s possible the mice weren’t experiencing the illusions, as we only activated a small number of neurons due to technical constraints.”
But the research is far from over. The next frontier? Behavioral tests. Adesnik envisions an experiment where these neurons are photo-stimulated to see if animals exhibit perceptual responses without any visual stimulus. “Right now, optogenetics limits us to activating only a handful of these neurons, which are relatively rare and scattered,” he explains. “But imagine if we could recruit three, four, or even ten times as many—we might finally observe behavioral responses. That’s the experiment we’re eager to conduct.”
This study not only deepens our understanding of how the brain constructs visual reality but also raises provocative questions. Could we one day manipulate these neurons to control perception itself? And what does this mean for our understanding of consciousness and the nature of reality? The debate is just beginning, and the implications are as fascinating as they are unsettling.
Nature Neuroscience, 2025. DOI: 10.1038/s41593-025-02055-5 (https://doi.org/10.1038/s41593-025-02055-5). Federica Sgorbissa, a science journalist specializing in neuroscience and cognitive science, continues to explore these cutting-edge discoveries for Italian and international audiences.
