http://www.scientificamerican.com/podcast/episode.cfm?id=adult-brain-shows-learning-changes-11-04-04

”They took four similar shades of green and blue and gave them made-up names—meaningless Mandarin monosyllables like sòng. Nineteen adults learned to match those names and shades in five sessions over three days, a total of an hour and 48 minutes. The scientists took MRI images of the subjects’ brains before and after the experiment. And they found a noticeable increase in gray matter volume in the regions known to be related to color vision and perception.”