“He discovered by chance that the strongest stimulus is a pattern of high-contrast dark and light bars.” He held up one hand and waved his fingers back and forth. “If you imagine my fingers were bars of light surrounded by complete blackness—if I move my fingers in front of your eyes, that fires up your whole visual cortex.”
To begin with, they used these moving images to train the mice.
The bars were projected onto a computer screen in front of them, and when they moved up and down, it was a cue to take a drink from a tube of water.
When they moved from side to side, they were to stop drinking.
The researchers used a sophisticated laser system to monitor brain activity through the mouse’s skull—identifying exactly which neurons were firing when it was looking at the projected images. “We can see the neurons that are encoding the visual stimulus,” Yuste explains.
