When he was asked, as a joke, to explain how the mind works in five words, cognitive scientist Steven Pinker didn't hesitate. "Brain cells fire in patterns", he replied. It's a good effort, but all it really does is replace one enigma with another mystery.

It’s long been known that brain cells communicate by firing electrical signals to each other, and we now have myriad technologies for recording their patterns of activity – from electrodes in the brain or on the scalp, to functional magnetic resonance scanners that can detect changes in blood oxygenation. But, having gathered these data, the meaning of these patterns is still an enduring mystery. They seem to dance to a tune we can't hear, led by rules we don't know.

Neuroscientists speak of the neural code, and have made some progress in cracking that code. They are figuring out some basic rules, such as when cells in specific parts of the brain are likely to light up depending on the task at hand. Progress has been slow, but in the last decade various research teams around the world have been pursuing a far more ambitious project. We may never be able to see the complete code book, they realised, but by trying to write our own entries, we can begin to pick apart the ways that different patterns correspond to different actions.

Albert Lee and Matthew Wilson, at the Massachusetts Institute of Technology (MIT) first helped to set out the principles in 2002. It progresses like this. First, we record from the brain of a rat – one of our closer relatives, in the grand tree of life – as it runs a maze. Studying the whole brain would be too ambitious, so we can focus our recording on an area known as the hippocampus, known to be important for navigation and memory. If you've heard of this area before it is probably because of a famous result which showed that London taxi drivers developed larger hippocampi the longer they had spent navigating the streets of England's sprawling capital.