A Thousand Brains: A New Theory of Intelligence

by Jeff Hawkins

In 1971, scientist John O’Keefe and his student Jonathan Dostrovsky placed a wire into a rat’s brain. The wire recorded the spiking activity of a single neuron in the hippocampus. The wire went up toward the ceiling so they could record the activity of the cell as the rat moved and explored its environment, which was typically a big box on a table. They discovered what are now called place cells: neurons that fire every time the rat is in a particular location in a particular environment. A place cell is like a “you are here” marker on a map. As the rat moves, different place cells become active in each new location. If the rat returns to a location where it was before, the same place cell becomes active again. In 2005, scientists in the lab of May-Britt Moser and Edvard Moser used a similar experimental setup, again with rats. In their experiments, they recorded signals from neurons in the entorhinal cortex, adjacent to the hippocampus. They discovered what are now called grid cells, which fire at multiple locations in an environment. The locations where a grid cell becomes active form a grid pattern. If the rat moves in a straight line, the same grid cell becomes active again and again, at equally spaced intervals.