Orange “O”s and Purple “P”s

"For most of us, our senses stay relatively separate: that is, we hear what we hear and see what we see. People with synesthesia, however, actually see words as colors, taste a particular flavor when they hear a familiar song, or experience other strong, automatic linkages between senses. The neurological underpinnings of the condition—how the brain connects two usually distinct senses—have remained a mystery. But researchers have now found a possible cause, they reported yesterday: neurons in the area responsible for the second sensation, such as the color that goes with the word, may be unusually excitable."

http://blogs.discovermagazine.com/80beats/2011/11/18/hyperactive-visual-cortex-neurons-may-cause-orange-os-and-purple-ps/