Scientists using tarantulas to unpick human fear have found that the brain responds differently to threats based on proximity, direction and how scary people expect something to be.
Researchers from the Cognition and Brain Sciences Unit in Cambridge, England used functional magnetic resonance imaging, or fMRI, to track brain activity in 20 volunteers as they watched a tarantula placed near their feet, and then moved closer.
Their 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, who led the study, said in a telephone interview.
Mobbs's team assessed the volunteers' brain activity during three sections of the study: first when the tarantula was in a segmented box near their foot and then moved either to nearer or more distant compartments of the box, and also when the spider walked 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.
He said there was more activity in the brain's panic response center when the tarantula crept closer than when it retreated, regardless of how close it was in the first place.
He explained that the volunteers were actually watching an elaborately rigged video of a tarantula which they believed was near their foot, since getting the spider to do the same thing for each volunteer would have been impossible.
The scientists also asked volunteers beforehand how scared they thought they might be of the tarantula, and found that those who thought they would be most scared had a false impression afterwards of how large the spider was.
The scientists think it may be this so-called "expectation error" that could be the key to people developing a phobia -- an irrational, intense and persistent fear of certain things, people, animals or situations.
"This may be one cognitive mechanism by which people acquire phobias," said Mobbs. He said that since the expectation of great fear appeared to make a person exaggerate the size of the threat in their mind, this could trigger a "cascade effect," distorting the other processes in the brain to react to a larger threat and panic yet more as it came closer.
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