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Fear In Humans Dependent On Awareness Of The Threat

How do we learn to fear danger? Neuroscientists have been studying this response for some time, using fear conditioning.

In this experimental procedure, a human or even a rat can be taught to fear a harmless stimulus by pairing it with an unpleasant one; if a rat consistently receives a mild electrical shock after hearing a tone, it will eventually develop a fear of the tone, even in the absence of the shock.

Now, researchers at University College London have analyzed the brain activity underlying learned fear in humans and have found that it is sensitive to whether the subjects are aware of the threat, and is affected by reflexive fear responses such as sweating and increased heart rate.

The results are reported in today's issue of Neuron.

A research team led by Hugo Critchley scanned the brains of individuals performing a task in which innocuous stimuli (pictures of faces) were associated with a loud unpleasant noise burst. Occasionally, the picture of a face was presented for such a short time that the subjects were not aware of it.

Critchley and colleagues observed that fear conditioning could still take place under these circumstances. They observed that when the threat was not consciously perceived, the accompanying brain activity was less in some areas than when it was perceived. However, in a region called the amygdala, long associated with processing emotions, the response was the same whether or not the subjects were aware of the threat.

Next, the researchers examined the brain activity of patients with localized brain damage whose only effect is to eliminate reflexive responses to fear, such as sweating and elevated heart rate (which are measured by lie detectors).

While these patients still learned to fear certain faces, Critchley and colleagues observed reduced brain activation compared to subjects without brain damage.

Critchley's findings suggest that the way our brains process fear is affected by our level of awareness of the threatening stimulus, and even by our reflexive, bodily responses to threats.

[Contact: Hugo D. Critchley]

14-Feb-2002

 

 

 

 

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