Someone with the condition known as grapheme-color synesthesia might experience the number 2 in turquoise or the letter S in magenta. Now, researchers reporting their findings online in the Cell Press journal Current Biology on November 17 have shown that those individuals also show heightened activity in a brain region responsible for vision.
The findings provide a novel way of looking at synesthesia as the product of regional hyperexcitability in the brain, the researchers say. They also provide a window into our understanding of individual differences in perception.
"Most of us tend to assume that we experience the world in the same way as everyone else, but synesthesia provides a clear example of a group that perceives the world in a fundamentally different way," says Devin Blair Terhune of the University of Oxford. "The majority of people do not have conscious experiences of color when they look at numbers, letters, and words, whereas synesthetes do. Studying these people can thus shed light on the brain mechanisms underlying conscious awareness."
Earlier studies had shown that synesthetes who experience color for numbers and letters also discriminate among colors better than those with other types of synesthesia. Those findings hinted that an overactive visual cortex might be in play.
Terhune's team, which is led by Roi Cohen Kadosh, found that average people do indeed require three times greater magnetic stimulation to their visual cortex than synesthetes do in order to experience phosphenes, transient flashes of light or other visual disturbances.
"We were surprised by the magnitude of the difference," Terhune said. "The synesthetes in our study displayed considerably greater levels of cortical excitability than our participants without synesthesia. These results point to a very large effect that may reflect a fundamental difference between the brains of those with and without synesthesia."
It's not that the enhanced excitability of the visual cortex is directly responsible for the experience of synesthesia, however. Further experiments showed that reducing the excitability of visual cortex in synesthetes actually increased their experience of colors with numbers. Meanwhile, increasing excitability in that brain region made the synesthesia more intense.
Terhune says they now suspect that the enhanced excitability of synesthetes' brains might be related to the development of the condition, but it doesn't produce the phenomenon in adults.
Ultimately, the findings might allow for treatments designed to reduce or eliminate the experience of synesthesia or to make it even more vivid, he says. The work also raises new questions in other fields that examine atypical perceptions, such as hallucinations, he says. "Might it be that the same principle is applying also there?"
Cell Press: http://www.cellpress.com
This press release was posted to serve as a topic for discussion. Please comment below. We try our best to only post press releases that are associated with peer reviewed scientific literature. Critical discussions of the research are appreciated. If you need help finding a link to the original article, please contact us on twitter or via e-mail.
By dipping live specimens in a chemical concoction, scientists are able to keep them alive in the vacuum conditions normally required for field emission scanning electron microscopy.
Astra Zeneca announces a research programme to develop a generation of medicines to treat the genetic causes of many debilitating diseases.
When patients with Parkinson's disease received an injection described as an effective drug costing $1,500 per dose, their motor function improved significantly more than when they got one supposedly costing $100, scientists reported on Wednesday.
New research shows that teenagers' brains aren't fully insulated, so the signals travel slowly when they need to make decisions. Neuroscientist Frances Jensen, who wrote The Teenage Brain, explains.
Researchers would use cohort of 1 million Americans pooled from smaller studies to study disease-gene links, improve personalized medicine
Some people have non-human neighbors of the usual, inspiring kind: Bald eagles and bears, sea lions and salamanders, the sort of creatures found in nature documentaries intoned by deep-voiced narrators who plead on our planet's behalf. But I live in New York City. The star of this show, a charismatic megafauna of my own particular wilderness, is none other than the rat — and what science is teaching us may change how we think of this oft-reviled creature, and maybe even ourselves.
An Oregon company has developed a high-tech process for turning sewage into pure drinking water. Now it's asking the state for permission to give its recycled water to a group of home brewers.
Skull cap of Homo sapiens found in Israeli cave hints at time and place of cross-species mingling
Is there a conscious generosity in how ravens or bats share food, or monkeys or elephants save others, or is it simply the selfish instinct of group survival?
DNA research into early canine remains also raises clues about migration patterns of ancient humans