November 9, 2010
Scientists Use fMRI, Tarantulas To Image Fear
British scientists have incorporated tarantulas into their study of how the human brain responds to fear based on proximity, direction and how scary people expect something to be.
Researchers from the Cognition and Brain Sciences Unit in Cambridge, England asked 20 volunteers to lie inside a functional magnetic resonance imaging (fMRI) machine. The scientists had each person view a screen showing a tarantula crawling closer...and...closer to the participant's feet.
As the arachnid got closer, MRI scans allowed researchers to see flashes of activity switch from the subject's prefrontal cortex -- a region associated with anxiety -- to a part of the midbrain known to involve intense fear.
When the tarantula retreated, the neural terror decreased, "regardless of the spider's absolute proximity," the study's authors wrote. So the study suggests, no matter how close the spider was, volunteers could relax once it moved away.
The results suggest that different components of the brain's fear network serve specific threat-response functions and could help scientists diagnose and treat patients who suffer from clinical phobias.
"We've shown that it's not just a single structure in the brain, it's a number of different parts of the fear network and they are working together to orchestrate the fear response," Dean Mobbs, leader of the study, who works at the MRC-Cognition and Brain Sciences Unit at the University of Cambridge Medical School, said in a telephone interview with Reuters.
The researchers assessed the subjects' brain activity during three sections of the study: first when the tarantula was in a segmented box near their foot and then moved to either nearer or further compartments of the box, and when the spider moved in different directions.
"It seems that when a spider is further away moves closer to you, you see a switch from the anxiety regions of the brain to the panic regions," said Mobbs.
There was more activity in the brain's panic response center when the tarantula crept closer than when it retreated, no matter how close it was in the first place, Mobbs said.
The volunteers were not actually in the fMRI unit with a tarantula, rather they watched an elaborate video of a tarantula which they believed was near their foot, since getting a spider to follow the same routine for each subject would have been impossible.
The researchers also asked the volunteers beforehand how scared they thought they would be of the tarantula, and actually found that those who said they would be most scared had a false impression afterwards of how large the spider was.
The team believe the major key in developing a phobia could be the so-called "expectation error," which is an intense and persistent fear of certain things, people, animals or situations that are typically not harmful.
"This may be one cognitive mechanism by which people acquire phobias," Mobbs told Reuters.
He said since the expectation of fear appeared to cause a person to exaggerate the size of the threat in their mind, this could trigger a "cascade effect," altering the other processes in the brain to react to a larger threat and panic yet more as it came closer.
The study, titled "Neural Activity associated with monitoring the oscillating threat value of a Tarantula," was published by the National Academy of Sciences.
When asked why the researchers used tarantulas, Mobbs replied: "The UK has one of the highest amounts of spider phobics in the world. This is despite the fact that we have no deadly spiders in the UK."
"I mainly used spiders because I have a slight fear of them," Mobbs admitted.
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