A baby fish watches a tasty cell swimming in front of it. Neurons fire in its brain, and it recognises a potential meal. Its eyes converge, it beats its tail, and it heads in for the kill.

Trillions of baby fishes have enacted this little tableau for half a billion years, but this individual is special. It has been altered by a team of Japanese scientists so that its neurons give off a flash of light whenever they fire. And since its head is transparent, any onlooker can see its brain activity. In doing the rather mundane task of capturing a meal, this fish is putting on a nifty real-time lightshow. It’s showing us what a thought looks like.

At the moment,