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 07 September 2008 01:45 BST

Brain's reaction to fear mapped

Friday, 24 Aug 2007 17:25
Complex systems in the brian control our reaction to fear
How the brain responds to different levels of fear has been mapped for the first time.

Scientists at the Wellcome Trust Centre for Neuroimaging in London discovered that the brain's response changes the closer a threat gets.

The fear response was seen moving away from strategic areas of the brain towards more reactive responses.

Writing in the journal Science, the researchers say this change occurs because different defence mechanisms are needed depending on the severity of the threat.

Participants in the study played a computer game where they are pursued by an artificial predator. If caught they received a mild electric shock.

Brain activity was measured using functional magnetic resonance imaging (fMRI).

When the predator was in the distance activity was observed in lower parts of the prefrontal cortex – an area just behind the eyebrows which increases during anxiety and helps control how people respond to threats.

But as the predator moved closer, activity shifted to an area of the brain responsible for what the researchers described as "more primitive behaviour" – the periaqueductal grey.

This area is linked to quick response mechanisms including running away and fighting.

Commenting on the findings, lead author Dr Dean Mobbs said: "The most efficient survival strategy will depend on the level of threat we perceive.

"This makes sense as sometimes being merely wary of a threat is enough, but at other times we need to react quickly. The closer a threat gets, the more impulsive your response will be – in effect, the less free will you will have."

The researchers also argue that problems with the brain's 'fear system' could explain why some people suffer from anxiety disorders and panic attacks.

"When our defence mechanisms malfunction, this may result in an over-exaggeration of the threat, leading to increased anxiety and, in extreme cases, panic," Dr Mobbs added.

"Although brain-imaging studies like ours cannot directly help to cure such disorders, they do improve our understanding of how the emotional system operates. This is the first step to helping people with anxiety-related disorders."
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