Synesthetes experience words, colors and numbers as having sounds, tastes and colors. For example, the letter “B” could be seen as red in someone’s mind and “O” could be a white letter while the name Joyce could taste warm and savory.

Study co-author David Brang said the research team is looking at the evolutionary benefits of synesthesia that have allowed it to survive natural selection. It is a trait that is not inherently useful so it hasn’t been selected for evolution itself, but instead “tagged along” with another trait.

The researchers used a tool called the Diffusion Tensor Imaging to see the connections between different brain regions, and found that the brains of synesthetes are wired differently. Synesthetes’ brains have increased connections between the associated senses.

The visual images of these connections could help explain why some forms of synesthesia only move in one direction, such as seeing numbers evoke color but not seeing colors evoke numbers.

The images could also help scientists explore the theory that all humans have the neural mechanisms for synesthesia, but that it is suppressed in most people.

Studies have found that synesthesia is seven times more common in artistic and creative individuals, leading scientists to think that synesthetes are better at bridging different ideas.

Brang said that a person who evokes colors from sound could listen to a musical piece and then paint what she sees, and it may be able to intuitively have the same significance for people who do not have the ability to see the colors.

“Even though you and I may not have synesthesia, the association of some colors and some numbers or colors and sound may make sense to us,” Brang said. “If you were to look at a painting and see some dark purplish sphere somewhere would you feel comfortable associating that with a flute or a bassoon? Most people would think a bassoon, a deep dark color would flow with a deep dark sound versus a wavering line for a flute, maybe a yellow color for a flute.”

Currently, the researchers are trying to discover whether synesthesia is present in animals as well, or if it is present in humans only.