At night, the brain doesn't switch off. Instead, it sorts through the day's events like a librarian arranging books on shelves. But where do those strange, sometimes nonsensical dream images come from? Many have assumed they're just random noise with no meaning.

A new computer model shows that randomness doesn't hinder: it helps. The brain takes random signals and turns them into useful experience. It's like a chef whipping up a new dish from whatever ingredients are on hand.

So sleep becomes a continuation of daytime learning. The brain isn't resting; it's working, just in a different way.