January 1, 2007 Cognitive neuroscientists have now documented hundreds of cases of synesthesia -- the condition in which one sense triggers the response of a different one. Using functional magnetic resonance imaging, behavioral neuroscientists are discovering the neurological basis of synesthesia by comparing patients' brains with those of healthy subjects.
What does yellow taste like? What color is the letter M? Not usual questions you hear, but some people's senses are actually joined together. It's called synesthesia. For years, synesthesia was dismissed as the product of someone's overactive imagination. But in the past decade, researchers have documented hundreds of cases of otherwise normal people ... Who have these extraordinary blended senses.
Daniel Eaton's grade school artwork is filled with bright colors. But page after page, the numbers and letters are colored consistently the same way. Fifteen years later, Eaton still sees each of his letters in very specific colors. What we see in black and white automatically "pops" off his page.
"It's kinda like trying to ignore, I don't know, someone in a really loud shirt in front of you. It just draws your attention," Eaton says.
At the synesthesia research group in Waterloo, Canada, cognitive neuroscientists study how synesthetes process the world around them. Researchers have many different theories about the cause of synesthesia, but there is a neurological basis.
"Synesthetes' brains are different, and things like functional magnetic resonance imaging can demonstrate that," Mike Dixon, a behavioral neuroscientist at University of Waterloo, tells DBIS.
In a British study, the MRIs were conducted on both synesthetes and non-synesthetes. When a researcher called out numbers, the region of the brain that recognizes color was activated in synesthetes. In non-synesthetes, the area that processes color did not respond.
Dixon says synesthesia is not in any way harmful. In fact, for some, there are clear benefits.
Jason Korzenko has what's called time-space synesthesia. Dates pop up on a 3D oval in front of him. Korzenko never forgets a birthday, anniversary ... or a class project.
"I think it's a gift," Korzenko says.
Dixon says, "Synesthetes do hold keys to how you and I experience the world." ...And unlock some of the mysteries of the human brain.
Researchers are unsure how rare synesthesia is. Some say as many as one in 2,000 experiences it, and other studies say it might occur as frequently as one in 200. Most researchers believe synesthetes are born with the joined senses and say it can run in families.
BACKGROUND: Some people can "feel" colors, not just see them; other people can taste, hear, or smell colors. This is the result of a rare neurological condition called synesthesia, in which two or more senses intertwine. Long dismissed as the product of an individual's over-active imagination, scientists in recent years have come to associate the phenomenon with a real neurological basis. The University of Waterloo is one of a small number of institutions where studies are being conducted on persons suffering from synesthesia. Anywhere between 1 in 200 and 1 in 2,000 people suffer from synesthesia of some sort.
TYPES OF SYNESTHESIA: There are many different types of synesthesia. For example, among those who associate letters and numbers with color, there are so-called "projector" synesthetes. In their perception, color can fill the printed letter or it can appear directly in front of their eyes as if projected on an invisible screen. In contrast, "associate" synesthetes see the colors in their "mind's eye" rather than outside their bodies. Another category is "perceptual" synesthetes, triggered by sensory stimuli like sights and sounds, while "conceptual" synesthetes respond to abstract concepts like time. For instance, a conceptual synesthete might describe the months of the year as a flat ribbon surrounding the body, each month being a distinct color.
WHAT'S THE CAUSE: There are several theories as the cause of synesthesia. One theory posits that irregular sprouting of new neural connections within the brain leads to a breakdown of the boundaries that normally exist between the senses. So synesthesia would be the collective "chatter" of sensory neighbors once isolated from each other. Another theory is that all infants begin life as synesthetes, born with immature brains that are highly malleable. Connections between different sensory parts of the brain exist that later become pruned or blocked as the infant matures. Still another theory states that synesthesia doesn't require extra connections, but arises when normally covert channels of communication between the senses are "unmasked" and cross into conscious awareness. None of these theories can be tested experimentally, because we do not yet have the technology to observe brain-connection changes in the living human brain, and determine how they relate to mental changes. Certain drugs, such as LSD or mescaline, can also induce synesthesia in some individuals.
Editor's Note: This article is not intended to provide medical advice, diagnosis or treatment.