Biologists are using light to explore the brain - and to alter it. Roland Pease meets some of the leading players in optogenetics, who use light-sensitive molecules to take direct control of neural systems in worms, flies, and maybe one day, humans. For some, it's a way of exploring the interplay of electricity and chemistry as neuron talks to neuron in complex brains. For others it opens the way to future therapies for conditions like motor neuron disease, in which dying nerves bring about paralysis, and epilepsy, brought about by runaway oscillations in brain waves.

(Photo: Elegans nemotodes, or round worms, undergo examination by project scientists at the Kennedy Space Center in Florida. Credit: Getty Images)