Brain uses decision-making region to tell blue from green

Early visual brain areas, language areas not crucial for color distinction

THE BLUES  Most people call the color on the left green and the three colors on the right blue. A brain area called the middle frontal gyrus is involved in making this distinction, a new study finds. 


C.M. Bird et al/PNAS, adapted by S. Egts

The human brain tells green from blue by relying on sophisticated decision-making areas of the brain, not those that first receive visual input. That finding, published March 3 in the Proceedings of the National Academy of Sciences, also hints that language isn’t necessary for categorizing colors.

Colors can carry important information about an environment — a red berry that’s poisonous or a baby who has turned blue because he’s dangerously ill, for instance. Because colors can be linked to survival, our brains go to great lengths to detect and distinguish them from one another, says neuroscientist Bevil Conway of Wellesley College in Massachusetts. “The immediacy of it [color] belies the fact that there’s lots and lots of computation taking place,” says Conway, who was not involved in the study. And those computations, particularly how the brain sorts the rainbow of hues into distinct color bins, are still somewhat mysterious.

“There has been a lot of debate about where color categories come from,” says study coauthor Anna Franklin of the University of Sussex in England. Some researchers believe that these color boundaries are hard-wired into the brain. Others think that these categories are a product of the environment, or a response to social influences. To find out how the brain actually handles these color distinctions, Franklin and colleagues asked participants to passively view swaths of variously hued blue or green squares while undergoing functional MRI.

On both sides of the brain, an area toward the top and front in a region called the middle frontal gyrus seems to be involved in telling blue from green, Franklin and colleagues found. These areas responded more strongly when people saw blue and green than when both colors were blue. Two different shades of blue did not spur this brain region to action. Because the middle frontal gyrus has been implicated in other sorts of categorizations, such as speech and dot patterns, the region may represent a more general assessor, Franklin says.

In the case of colors, the middle frontal gyrus is notable for what it’s not. The brain isn’t relying on the visual cortex — where information from the eye travels first before being analyzed by other brain regions — to tell colors apart. Nor is the brain relying on language centers, which some people believe to be necessary for color categorization. For those reasons, the finding is “a very important and very provocative step,” Conway says.

The brain sorts colors into bins without the need for language, the finding suggests. “We’re actually able to do that chunking even if we’re not explicitly naming the colors at the time,” Franklin says. 

The results may help scientists ultimately figure out how the brain interacts with its surroundings. “The world is one big continuum of information, yet our brain somehow has to parse that and make sense of it,” Franklin says. “And to do all that, you need to categorize.”

Laura Sanders is the neuroscience writer. She holds a Ph.D. in molecular biology from the University of Southern California.

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