We have luminescent jellyfish to thank for one advance in neuroscience. By sticking the genetic code for the jellyfish's green fluorescent protein in cells, researchers made them glow green (a neat trick that won the 2008 Nobel Prize in chemistry). Most importantly, this could be done in living animals and tissues, allowing researchers to watch neurons in action. To sort out the tangle of brain cells, molecular chemists next searched out fluorescent proteins in other colors, and found innovative ways to make neurons glow in slightly different hues.

This "brainbow" image traces the long axons of individual neurons in a gorgeous array of colors. The image, produced in 2007, shows motor neuron axons stretching away to the muscles they control.