Scientists create the largest map of a mouse’s brain, revealing 84,000 neurons and 500 million synaptic connections in unprecedented detail

In a remarkable achievement, researchers have produced a map of a mouse’s brain that showcases the complexity of 84,000 neurons, offering insights into the intricate wiring of the brain’s visual cortex. This research provides the most comprehensive functional map of a brain to date, with scientists identifying how neurons are interconnected through 500 million synaptic junctions. The breakthrough was made possible by using advanced imaging techniques, including electron microscopy and artificial intelligence, to trace how neurons communicate in a 3D reconstruction of brain activity.

Led by Forrest Collman from the Allen Institute for Brain Science, the team employed a mouse engineered with glowing neurons that light up when activated. The mouse watched a series of video clips—ranging from movies to nature documentaries—while researchers recorded neuron activity in the visual cortex. This allowed them to capture real-time brain activity and map how the neurons were firing during specific visual stimuli. The result is a dataset that provides a detailed look into the functional circuits of the brain.

The research team at Baylor College of Medicine began by showing the mouse a range of video clips designed to stimulate its brain. The mouse, genetically modified to produce glowing neurons, provided a visual record of brain activity as individual neurons lit up in response to the images. This data was then sent to the Allen Institute, where it was used to analyze a small portion of the mouse's visual cortex.

In a painstaking process, the researchers sliced this tissue into 25,000 thin layers and used electron microscopes to take nearly 100 million high-resolution images of these layers. The 3D images were then reconstructed and analyzed by scientists at Princeton University, who used artificial intelligence algorithms to trace the wiring of neurons and identify connections between them. These individual connections were color-coded to make them easier to track, allowing researchers to trace how signals moved through the brain’s circuitry.

The researchers estimated that if these neural connections were stretched out, they would cover more than 3 miles (5 kilometers). This incredible level of detail allowed the scientists to connect brain structure with activity, providing insights into how the visual cortex processes information.

This unprecedented map of the mouse brain represents a significant milestone in neuroscience, providing critical data for understanding brain function. By tracing the connections between neurons, the researchers hope to uncover new insights into how the brain operates. Understanding these neural networks is vital for advancing our knowledge of brain disorders like Alzheimer’s, autism, and schizophrenia, where the brain’s wiring can become disrupted.

Clay Reid, a scientist at the Allen Institute, explained that knowing how neurons are wired together is essential for testing hypotheses about how they perform specific functions. The researchers believe this work will be a foundational step toward identifying abnormal neural patterns that contribute to brain disorders. They compare the project to the Human Genome Project, which mapped genes and led to new gene-based treatments.

Sebastian Seung, a neuroscientist and computer scientist at Princeton University, emphasized that the technologies developed in this project could eventually help scientists identify abnormal patterns of connectivity in the brain that lead to diseases. This could ultimately open the door for new treatments based on a deeper understanding of brain structure and function.

The mapping effort involved over 150 scientists from institutions around the world, organized under the Machine Intelligence from Cortical Networks (MICrONS) consortium. The research was funded by the National Institutes of Health’s BRAIN Initiative and the Intelligence Advanced Research Projects Activity (IARPA). The findings have been made publicly available, creating a valuable resource for researchers worldwide.

Harvard neuroscientists Mariela Petkova and Gregor Schuhknecht, who were not involved in the project, praised the work for its potential to uncover new insights into neural networks that underpin cognition and behavior. With the dataset open to the global scientific community, it is expected to accelerate progress in understanding the brain’s structure and function. This open-access approach ensures that the data can be used by researchers to investigate new areas of brain science, including the development of therapies for neurological disorders.

By making the data publicly accessible, the researchers hope to spark further breakthroughs in brain science and inspire a new era of discovery, similar to how the Human Genome Project revolutionized genetics. The ultimate goal is to map the entire mouse brain and eventually apply these findings to human brain research, furthering our understanding of cognition, behavior, and mental health.