Late one night in the summer of 2004, a Stanford PhD student named Ed Boyden flashed a pulse of blue light on to a genetically modified rat neuron. To his delight, the neuron fired in response.

“It was one in the morning and it was almost too good to be true,” recalls Boyden, who has since launched his own bioengineering lab at MIT.

His seminal experiment has revolutionised neuroscience. Being able to excite neurons – the cells that send and receive signals in the brain – with simple flashes of light has given researchers unprecedented control over the brain’s workings.

The technique – dubbed ‘optogenetics’ – is enabling scientists to tease apart how each of the 86 billion-odd neurons stuffed into our skulls makes us tick. Others have more practical applications in their sights, hoping to take optogenetics out of the lab and into the clinic to treat conditions including blindness, chronic pain and epilepsy.