Milo and the Invisible Map
Milo was not an ordinary mouse. He lived in a big, square arena in a quiet neuroscience lab, and although Milo had never seen a map, he carried one inside his head. A living, breathing map made of tiny, humming neurons. Each morning, when the lights clicked on, Milo would scurry out from his nest and explore. As he padded across the floor, certain neurons deep in his brain—the place cells in his hippocampus —would flicker to life. One would fire when Milo passed the north wall. Another would spark when he sniffed near the food bowl. Each place cell was like a sentry, shouting, “Here! You’re here!” at a specific location. But that wasn’t the only magic happening inside Milo’s head. Further back, in the entorhinal cortex , a different army of neurons—the grid cells —were hard at work. These cells didn't just fire at one location. No, grid cells lit up in a beautiful, repeating pattern , like the crossing points of an invisible honeycomb. As Milo moved, each step activated a prec...