Inside a Mouse’s Mind: Discovering a Hidden Universe

Have you ever heard someone dismissively say, "They've got a mouse brain" to imply someone isn't very smart? Neuroscientists at Princeton University decided to tackle this stereotype and see if a "mouse brain" is really synonymous with emptiness.

Focusing on the tiniest fraction of a mouse's brain, a mere cubic millimeter from its visual region, they set out to see what lurks within this minuscule, sesame seed sized piece. After all, isn't a mouse just nibbling on cheese all day?

A Hidden Universe in a Grain of Brain

To their surprise, when this tiny piece was charted out digitally, it revealed an intricate network of 84,000 neurons communicating through a staggering 500 million synapses, resembling a massive web of branches. This achievement is monumental in technological terms. The computer or phone you're reading this on doesn't come close to this level of complexity in terms of connections and technological sophistication.

Neuroscientist Carl Zimmer wrote in The New York Times about the challenge of comparing mouse brains to the infinitely more sophisticated human brain: "The human brain is so complex that even scientific minds struggle to understand it. A piece of neural tissue the size of a grain of sand can be packed with hundreds of thousands of cells connected by kilometers of wires. In 1979, Nobel laureate Francis Crick determined that the anatomy and activity within just one cubic millimeter of brain material would be beyond what humanity could decipher for ages, suggesting that it's 'pointless to ask for the impossible,' as Dr. Crick wrote."

Achieving the Impossible

"However, forty-six years later, a team of over 100 scientists achieved the seemingly impossible by recording cellular activity and mapping the structure in a cubic millimeter of mouse brain, less than one percent of its full volume. In accomplishing this feat, they collected 1.6 petabytes of data, the equivalent of 22 years of continuous high definition video."

Picture this video analogy: Have you ever waited a long time to download a high definition video? How long was it? An hour? Now imagine a high definition video that plays for 22 years. That's just the data storage capacity in that grain sized piece of a mouse brain. Now, imagine what could be inside a human's brain.

From Film Critic to Digital Model

Margarita Basi, another researcher, discussed the process with Smithsonian Magazine: "We had to end the mouse's career as a film critic. Right after it watched the movie, before the brain had a chance to solidify, we extracted a cubic millimeter of brain tissue and sliced it into approximately 28,000 layers, each one 400 times thinner than a human hair. Each layer was digitally photographed, and artificial intelligence compiled these 28,000 images into a 3D diagram."

The diagram is available online, and when you view it, it feels like witnessing a grand factory far surpassing all human industries, and remember, it’s just one millimeter from a mouse’s brain.