What makes us human? Many would point to our ability to speak, to imagine, to plan, to create art, or to hold memories of the past while envisioning futures that do not yet exist. These abilities are not mere accidents—they are rooted in the remarkable design of our brain.
One of the defining features of the human brain is the cerebral cortex, the outer layer of gray matter responsible for higher thought. But unlike most animals, our cortex is not smooth. Instead, it is covered in folds, grooves, and ridges that expand its surface area and create the intricate landscape of thought. These wrinkles are more than just fascinating patterns—they are the scaffolding of intelligence, shaping the way we think, feel, and experience the world.
A new study published in Nature Communications sheds light on how these folds form, offering a window into the mysterious origins of human cognition and perhaps the evolution of our species itself.
Why Wrinkles Matter
Most animals, even those with sizable brains, have smooth cerebral cortices. Humans, however, along with some primates, whales, dolphins, and pigs, possess a brain surface rippling with grooves (called sulci) and ridges (gyri). These folds are not decorative—they are functional. By crumpling the cortex into a compact space, the brain dramatically increases its surface area without expanding its size.
This extra surface area allows for far more neurons, meaning more processing power and greater complexity of thought. Our capacity for language, imagination, abstract reasoning, and creativity is deeply tied to this folded structure. Yet, for decades, scientists have wrestled with a simple but profound question: How do these folds form in the first place?
Clues from Tiny Brains
To answer this mystery, researchers at the Max Planck Institute for Biological Intelligence turned to an unlikely model—the mouse brain. Unlike humans, mice have smooth cortices, which makes them useful for studying what happens when folding begins to emerge.
Earlier work by Rüdiger Klein’s team showed that removing certain adhesion molecules—the proteins that help neurons migrate together—changed the way brain cells moved during development. Without these molecules, neurons spread out more loosely, and astonishingly, the normally smooth mouse cortex began to wrinkle, forming grooves reminiscent of the human brain.
This hinted at a deeper truth: folding may be driven not by a single mechanism, but by a delicate interplay of cell numbers, migration, and organization.
When Cells Shape the Landscape
Building on their earlier work, the researchers added another layer to the puzzle: increasing the number of progenitor cells—the early-stage cells that give rise to neurons. When they combined this boost in cell numbers with altered migration, the mouse brains developed even more pronounced folds, with strikingly complex patterns of grooves and ridges.
Through genetic tools, single-cell sequencing, and computer simulations, the team uncovered that not all progenitor cells behave the same way. For example, when intermediate progenitors were increased, sulci (grooves) formed more readily. In contrast, boosting apical progenitors favored the formation of gyri (ridges).
This finding suggests that the precise mix of cell types is as important as their numbers, shaping the architecture of the brain like sculptors working together to form a landscape.
The Power of Combination
The study’s first author, Seung Hee Chun, summarizes it best: “It’s thought that our brain’s wrinkles form through a mix of rapid cell growth and the movement of neurons as the brain develops. But how these processes work together to create the brain’s characteristic grooves and ridges was not well known. Our study suggests that cell movement, how tightly neurons migrate together, and how densely they are packed all contribute. It’s the combination of these factors—rather than any one alone—that drives things.”
In other words, folding is not the result of a single switch being flipped. It is an orchestra of biological forces—genetic, cellular, and mechanical—working together to create the very canvas of human thought.
Beyond Wrinkles: What This Means for Us
These findings reach far beyond the mouse lab. They provide critical insight into how the human brain develops, why its structure varies from person to person, and how certain developmental conditions may arise.
For example, some neurological disorders are linked to unusual patterns of cortical folding. Understanding the cellular processes that govern these wrinkles could guide future research into brain health, from developmental disorders to neurodegenerative diseases.
Moreover, these discoveries touch on profound questions of human evolution. Why do some species develop wrinkled brains while others remain smooth? How do different folding patterns relate to intelligence, behavior, or sensory abilities? And what might this reveal about the extraordinary trajectory of the human mind?
A Map of Individual Brains
Another fascinating implication of this research is its potential to explain why no two human brains are exactly alike. Even among individuals, the folds of the cortex vary, like fingerprints. These variations may influence differences in cognition, personality, or even susceptibility to mental illness.
As Rüdiger Klein notes, “Even between humans, the folding patterns of the cortex can vary greatly from person to person. Understanding what drives these differences could help us better learn how the brain develops, and how its shape relates to aspects such as function, evolution, behavior, and health.”
The brain’s wrinkles, then, are more than biological curiosities. They are signatures of individuality, shaping who we are and how we experience the world.
The Next Frontier of Brain Science
The mystery of the brain’s folds is far from solved. This study highlights the importance of cellular diversity and migration, but countless other factors—mechanical forces, genetic programs, chemical signals, even evolutionary pressures—are likely at play.
Future research will continue to unravel these mysteries, bringing us closer to understanding not only how the brain takes shape, but also why it gives rise to consciousness, creativity, and the uniquely human experience of life.
Science often progresses in small steps, but every step opens new doors. By studying the humble wrinkles of the brain, we are not just decoding anatomy—we are exploring the origins of thought itself.
