In a landmark achievement for neuroscience, researchers have created the most detailed 3D map of a working brain segment ever produced. The result, unveiled by the MICrONS Project, represents the first time scientists have been able to map both the structure and activity of brain tissue at such a scale.
The project, backed by the U.S. Intelligence Advanced Research Projects Activity (IARPA) and involving more than 150 researchers from institutions including Baylor College of Medicine, Princeton University, and the Allen Institute, focused on a cubic millimetre of the mouse brain's visual cortex—roughly the size of a grain of sand.
Combining structure and function
Researchers began by recording the brain activity of a live mouse as it was exposed to visual stimuli, including short video clips. Following this, the corresponding brain tissue was extracted and sliced into over 25,000 layers, each thinner than a human hair. High-resolution electron microscopy was used to image every slice.
At Princeton, the data was processed using artificial intelligence and machine learning tools to reconstruct the entire volume in 3D. The result is a dataset containing more than 200,000 neurons, 4 kilometres of axons, and over 523 million synapses. In total, the data amounts to 1.6 petabytes—equivalent to roughly 22 years of continuous HD video.
What distinguishes this project is the inclusion of functional data. Previous efforts, such as the FlyWire project, were limited to anatomical structures. MICrONS goes further, allowing researchers to examine how neural networks operate during specific tasks.
Implications for research and medicine
The ability to view both the structure and function of such a large volume of brain tissue opens new avenues for understanding how neurons communicate and organise during activity. Early findings from the project reveal complex patterns of inhibition, where inhibitory neurons selectively target specific excitatory cells, rather than acting uniformly.
This could lead to a more refined understanding of how brain circuits operate in both health and disease. The data may help in studying neurological conditions like Alzheimer’s, Parkinson’s, and autism, all of which involve disruptions in neural communication.
A foundation for future studies
The MICrONS dataset is now publicly available for researchers through the MICrONS Explorer platform. It is expected to serve as a foundational resource for neuroscientists aiming to model brain activity or develop new tools for analysing neural function.
Described by IARPA as a “moonshot” investment, the project is already being compared to the Human Genome Project in its scope and potential impact. Researchers say it lays the groundwork for broader efforts to map the human brain in future.
