For a special 2 percent of the population, the world seems a little more surreal.

In a condition called synesthesia, there are extra connections among parts of the brain related to individual senses. The actual experience varies, but some say that numbers, letters, sounds or even faces appear to have colors associated with them that most people don't see. For some, it's just an association; others actually do think they see those colors. Here's how color vision works, by the way.

Now, scientists have new clues about how the brains of people with synesthesia give rise to these bizarre-seeming perceptions. Synesthesia expert V.S. Ramachandran of the University of California, San Diego, presented the findings this week in a press conference at Neuroscience 2010, the Society for Neuroscience meeting.

Among the findings are that the hippocampus, a brain region essential for memory, has extra connections in people who say that certain numbers remind them of particular colors. In contrast, sensory areas of the brain show greater connectivity in those who believe that they are actually seeing these colors in the numbers. Thus, there are different neural mechanisms for these two kinds of synesthesia, finds Romke Rouw of the University of Amsterdam.

This study also found that people with synesthesia generally have more white matter, indicating increased connectivity, in the fusiform gyrus, a brain area involved in the processing color, numbers, letters and faces.

"It doesn't get any better in neuroscience, when you get a quirky, odd, crazy psychological phenomenon and actually pin it down to changes on wiring in the brain, based on genes," Ramachandran said.

Research presented by David Brang at the University of California, San Diego suggests that the synesthestic brain uses this increased connectivity to transfer information from one area to another. He and colleagues used magnetoencephalography, a method of recording neural activity. They showed that activity in the brains people with synesthesia flows from the visual areas to the visual processing areas in recognizing a number, and then to the brain's color area about five to 10 milliseconds later. This did not happen in participants who do not have the condition.

Ramachandran and colleagues have also identified a gene that appears to be involved in the condition. Although synesthesia does not necessarily make people more artistic, but it does seem to pop up among noted creative people; for example, novelist Vladimir Nabokov, physicist Richard Feynman and composer Franz Liszt. Ramachandran's theory is that, genetically, synesthesia has persisted throughout the centuries in humans because of its association with creativity.

Besides seeing colors where they wouldn't be otherwise, other reported effects of synesthesia are even more mysterious: For example, some associate numbers with "male" and "female."

Many parents of children with autism e-mail Ramachandran and Brang asking them about a link between autism and synesthesia, because their children appear to have sensory abnormalities resembling synesthesia. The link has not been scientifically proven, but Brang believes there still could be some connection.