One of the greatest mysteries in neuroscience is how the brain’s physical structure gives rise to thoughts, behaviors, and emotions. At first glance, the question seems straightforward: neurons are connected in a precise way, and those connections create the patterns of activity that drive everything we do. But is anatomy alone enough to explain the mind?
A recent study of a tiny roundworm called Caenorhabditis elegans—a microscopic creature no bigger than a grain of rice—suggests the answer is more complicated. The worm’s nervous system is one of the simplest known to science, consisting of just 302 neurons compared to the roughly 86 billion in a human brain. Yet even in this miniature model, structure alone does not fully dictate function.
This discovery challenges long-held assumptions and forces us to rethink what it really means to “map the brain.”
A Worm with a Known Connectome
C. elegans has been a favorite subject of neuroscientists for decades because it provides a rare gift: a complete wiring diagram of its nervous system. Using painstaking electron microscopy, scientists mapped every single connection between its neurons, creating what is called a “connectome.”
With the connectome in hand, one might expect that predicting how the worm’s nervous system works would be straightforward. After all, if you know how every road in a city is laid out, shouldn’t you be able to predict how traffic moves?
But the new study revealed something surprising: the flow of neural signals does not always follow the neatly drawn pathways of the connectome.
Mapping Function Beyond Structure
To probe this mystery, researchers went beyond static maps. They stimulated individual neurons with light and tracked the resulting activity through calcium imaging, a technique that lets them see which neurons fire in response. This produced a second map—not of structure, but of function: a dynamic atlas of how signals actually travel through the nervous system.
When they compared this functional map to the anatomical connectome, the two did not align as neatly as expected. Some signals bypassed predicted routes. Others found shortcuts or followed pathways that looked unlikely on paper. It was as if the city map showed one story, while the real traffic patterns told another.
Interestingly, certain parts of the nervous system did maintain a close match. The pharynx, the worm’s feeding organ, showed functional flows that mirrored its structural connections. But overall, the brain’s behavior could not be explained by structure alone.
The City and Its Traffic
The analogy of city planning is useful here. A map of roads, intersections, and highways tells you what routes are possible. But it doesn’t capture rush-hour traffic jams, sudden detours, or the way people prefer certain shortcuts. The connectome is the city map; the functional flow of signals is the traffic.
In the worm, as in us, what matters is not just the roads but how information actually moves through them. And that flow is shaped by far more than static structure—it is influenced by the strength of connections, timing of signals, neuromodulators, and the overall state of the system.
Why This Matters for Humans
At first glance, it may seem odd to care so deeply about the brain of a worm. But what happens in C. elegans offers profound lessons for understanding the human brain.
Our brains are vastly more complex, with billions of neurons and trillions of connections. Mapping the human connectome is already an ambitious global project, but this study shows that even if we succeed, it won’t be enough. Just as in the worm, knowing structure is only half the story.
This has enormous implications for how we study neurological and psychiatric disorders. Conditions like Alzheimer’s disease, schizophrenia, or epilepsy are not just about missing or damaged connections—they are also about disrupted signaling patterns. If we only look at the map and not the traffic, we may miss the true nature of the problem.
A Deeper View of the Brain
What the worm teaches us is humbling: the brain cannot be reduced to wiring diagrams. It is a living, dynamic system, where structure provides the possibilities, but function reveals the reality. Signals weave through neurons in ways that are flexible, adaptive, and sometimes unpredictable.
Understanding this interplay may one day help us design better treatments for mental illness, develop more advanced brain–computer interfaces, and even shed light on the age-old mystery of consciousness itself.
Looking Beyond the Map
The study of C. elegans offers a reminder that science often progresses by challenging assumptions. We once thought that if we could map every neuron, we would hold the key to understanding the brain. But the worm whispers a different truth: structure matters, but it is not destiny.
Function emerges from complexity, from the rhythms and flows of living tissue. To truly understand the brain—whether of a worm or a human—we must learn to see not just the map, but the movement. Only then will we begin to grasp how the machinery of matter becomes the miracle of mind.
More information: Sophie Dvali et al, Diverging Network Architecture of the C. elegans Connectome and Signaling Network, PRX Life (2025). DOI: 10.1103/6wgv-b9m6
