An international team of scientists has achieved what seemed unattainable for decades: draw the first complete map of brain development, from its first cells to maturity. The project, promoted by the BRAIN initiative of the United States National Institute of Health (NIH), and published in 12 studies in Nature, not only reconstructs brain growth from embryo to adulthood, but also offers a new framework for understanding how and when neurological disorders appear.
The discovery, comparable in scope to the Human Genome Project, provides a mapping of millions of cells in different species, from mice to humans, and describes how they divide, migrate, specialize and communicate with each other. Or put another way: for the first time, we can see how the brain builds itself. It is about a map, but not only to locate the starting point of our mind, but also that of neurological diseases and disorders.
Neurodevelopmental diseases, such as autism, ADHD or schizophrenia, affect about 15% of children and adolescents in the world, according to the study authors. Understanding how brain cells are formed during pregnancy and childhood allows us to observe when the error occurs, when a cell takes a detour or a connection is poorly established.
“This body of work gives us a detailed blueprint of how different types of brain cells emerge and mature,” says Hongkui Zeng, director of Brain Sciences at the Allen Institute and leader of the study. By understanding when and where critical genes are activated during development, we can begin to unravel how disruptions in that process lead to disorders. like autism or schizophrenia.”
The Zerng team has analyzed more than 1.2 million brain cells, with sequencing and visualization technologies that allow each of them to be followed as if they were passengers in a vast neuronal transport system: they are born at a “station” in the brain, travel throughout entire regions and stop right where they should be part of the circuit.
Among the most notable works is the analysis of the GABAergic neurons, a type of cells that act as brakes on the nervous system. These neurons regulate brain excitation and allow different regions to communicate without “collapsing.”
Allen Institute scientists have reconstructed their family tree, identifying how they emerge, disperse, and transform into specialized subtypes. The most surprising finding is that some continue to develop long after birthespecially in areas of the brain linked to learning, decision-making and emotions. This suggests that the infant brain maintains a longer capacity for reconfiguration than previously believed, which could open a broader therapeutic window to treat developmental disorders.
Another study focused on the development of the visual cortex. By following more than 770,000 individual cells, the authors discovered that the brain does not finish organizing itself before birthbut continues to form new cell types even afterward, especially at key moments: when the animal opens its eyes for the first time or when it begins to process visual stimuli from the environment.
“Understanding development in these stages is crucial, because it reveals when the brain is most vulnerable,” says Tomasz Nowakowski, co-author and professor of neuroscience at the University of California, San Francisco. “These maps help us identify when errors in maturation can lead to neurodevelopmental disorders.”
The discovery reinforces a powerful idea: early experiences physically shape the brain. Seeing, hearing or interacting with others during childhood is not just learning, it is literally brain architecture.
In another study, scientists used a technique called BARseq, which allows “reading” active genes within millions of neurons in the brain. Thanks to this they discovered that Each brain area has a unique cellular signature, a combination of neuronal types that defines its functionas if each region had its own fingerprint. The most interesting thing: sensory experience directly influences this specialization. That is, the simple act of seeing or hearing alters the genetic identity of developing brain regions.
“These maps are a fundamental achievement – concludes Joshua Gordon, former director of the National Institute of Mental Health and current chair of Psychiatry at Columbia University -. “They give us the structure upon which we can build a deeper understanding of autism, schizophrenia and other disorders that originate during brain development.”
With this work, scientists have created a kind of “Google Maps” of the growing brain, in which each cell has a location, an identity and a history. If before we knew the adult brain as a political map, with its delimited regions and established functions, this project offers us the meteorological map of thought: shows how neuronal storms form, how they calm down, and at what point hurricanes of illness can break loose.
The brain, now we know, It is not built at once, but it rehearses itselfadjusting its circuits with each stimulus. And understanding that process not only brings us closer to curing autism or schizophrenia, but also to something deeper: understanding how we became who we are.