Scientists Map Mouse Brain Wiring, Revealing Galaxy-Like Structure

In a groundbreaking study, scientists have created the largest functional map of a brain to date, revealing the intricate connections of 84,000 neurons in a mouse’s brain. Using a piece of brain tissue the size of a poppy seed, researchers traced how these neurons communicate through 500 million junctions known as synapses.

Published in Nature on Wednesday, the massive dataset represents a significant step in understanding how our brains function. The 3D reconstruction, color-coded to highlight different neural circuits, is now available for scientists and curious minds alike.

“It’s awe-inspiring, much like looking at galaxies,” said Forrest Collman from the Allen Institute for Brain Science, one of the lead researchers. “We’re looking at one tiny part of a mouse’s brain and seeing its beauty and complexity in these neurons and their countless connections.”

Neurons in the brain govern everything from thinking and feeling to movement and speech, sending signals through axons and dendrites across synapses. However, little is known about how specific neural networks are wired to perform tasks, or how disruptions in these networks may contribute to disorders like Alzheimer's and autism.

“You can make a thousand hypotheses about how brain cells do their job, but you can’t test those hypotheses without knowing how they’re wired together,” explained Clay Reid of the Allen Institute.

The project, involving more than 150 researchers globally, focused on mapping neurons in the mouse brain’s visual cortex. The process began with showing a mouse video snippets of sci-fi films, sports, and nature. Scientists at Baylor College of Medicine used a mouse engineered with glowing neurons to record brain activity as the animal watched these clips.

At the Allen Institute, scientists analyzed the brain tissue by slicing it into more than 25,000 ultra-thin layers and capturing nearly 100 million high-resolution images using electron microscopes. These images revealed the complex neural wiring, which was then reconstructed in 3D. Princeton University scientists employed artificial intelligence to trace and color-code the neural connections, estimating that if the wiring were laid out, it would span over 3 miles.

The researchers believe this mapping could ultimately help uncover the neural disruptions behind brain diseases. The project is a foundational step toward the full mapping of the mouse brain, similar to the breakthroughs achieved by the Human Genome Project.

“This marks a major leap forward in understanding the neural networks that underlie cognition and behavior,” said Sebastian Seung, a lead researcher from Princeton.

The data, shared publicly, is expected to be a valuable resource for future research into brain disorders. The project was funded by the NIH’s BRAIN Initiative and IARPA’s Intelligence Advanced Research Projects Activity.