"We could create devices sensitive to any physical energy," said Prof Nicolelis, from the Duke University Medical Center in Durham, North Carolina. "It could be magnetic fields, radio waves, or ultrasound. We chose infrared initially because it didn't interfere with our electrophysiological recordings."
At first, the rats scratched at their faces, indicating that they were interpreting the lights as touch. But after a month - as shown in these videos - the animals learned to associate the signal in their brains with the infrared source.