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Charlotte's Web of Fear

Brain responds faster to potential threats like spiders and snakes, says study

MONDAY, Sept. 24, 2001 (HealthDayNews) -- Can't stand spiders and snakes? Even if you don't have a phobia, new research suggests that these creepy-crawlies trigger activity in your brain faster than a more cuddly object.

According to Swedish researchers, that quick response could be your brain's evolutionary way of helping you survive.

In the September issue of the Journal of Experimental Psychology: General, Arne Ohman and his colleagues at the Karolinska Institute in Stockholm looked at whether images of potentially phobic stimuli, like snakes and spiders, captured attention faster than neutral stimuli, like flowers or mushrooms.

Ohman, a professor of psychology and clinical neuroscience, showed volunteers fear-associated images of snakes and spiders in arrays of neutral pictures, and vice versa, and asked the participants to identify either the negative or neutral stimuli.

They tested these images on a group of 25 men and women, ranging in age from 21 to 41, and in a second group of 30 people between the ages of 16 and 37.

The participants, all of whom said they had no phobias, responded to the snakes and spiders approximately 100 milliseconds faster than they did to neutral images, says Ohman.

The images were also shown to a third group of 130 men and women who admitted they had phobias of snakes or spiders. Ohman found that people with phobias recognized the objects of their fears even faster than those without phobias. Those with phobias perceived the threat 100 milliseconds faster than those without phobias, and 200 milliseconds faster than they recognized neutral stimuli.

Philip Merikle, a professor of psychology at the University of Waterloo in Waterloo, Ontario, is familiar with the Swedish study.

"What we're actually aware of, at any point in time, is . . . determined by the meaning of information that's being extracted from the environment," says Merikle. "That means you are analyzing all of this information in your environment at a very high level of meaning outside of awareness."

"We're particularly sensitive to things that have negative connotations," he says. "If I'm a snake-phobic, I'm particularly sensitive to stuff related to snakes. If I'm spider-phobic, that will do it."

Both Merikle and Ohman have also found that humans respond the same way to angry faces, another example of a potentially threatening stimulus. And they agree that from an evolutionary point of view, it makes sense.

"This is probably something that goes back a long way in evolution," says Ohman. "It's something that was acquired already by the first mammals that are small and relatively vulnerable in a world ruled by great reptiles. This is about 200 million years ago, when dinosaurs ruled the world."

He speculates that reaction may be partially "hard-wired" into our brains, and that we may also create these behavior patterns at a young age.

"We may have a genetic predisposition to quickly discover and respond to this type of potentially life-threatening stimuli," says Ohman. "Also, it's probably enhanced by learning. If you have bad experiences in relation to snakes or spiders, then you're probably conditioned to this type of attention response."

Previous brain-imaging studies examining what parts of the brain respond to fearful stimuli point to a small structure in the temporal lobe called the amygdala, and Ohman suspects that it may play an important role in these phobia scenarios.

Ohman is now studying whether positive stimuli, like erotic images, trigger a similarly rapid response.

What To Do

You can check out the Whole Brain Atlas, or visit the Web site for the Society for Neuroscience to find out about fear and the amygdala.

The National Institute of Mental Health provides information on anxiety disorders and phobias.

SOURCES: Interviews with Arne Ohman, Ph.D., professor of psychology, chairman, Department of Clinical Neuroscience, Karolinska Institute, Stockholm, Sweden; Philip M. Merikle, Ph.D., professor and chairman, Department of Psychology, University of Waterloo, Waterloo, Ontario; September 2001 Journal of Experimental Psychology: General
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