Studying the neural basis of perception is tricky, but what if the output of that neural activity were on display? That, says Sam Reiter and his team from The Max-Planck Institute for Brain research, is preciely what cuttlefish do. Cuttlefish have the ability to alter their appearance using finely controlled colour-changing cells in their skin. These cell are directly controlled by neurons extending from the brain. The team monitored changes in the state of the colour-changing cells with high resolution cameras, which allows them to track the activity of tens of thousands of neurons simultaneously, for the first time.