Study finds brain's 'fear switch'

WASHINGTON - US researchers say they have identified an "on-off" switch in the brain that controls the emotional response to fear, and said it might some day be manipulated to help patients with anxiety disorders.

The team at Columbia University Medical Centre used a simple attention test and a type of real-time brain scan called functional magnetic resonance imaging, which can catch the brain in action.

It showed an area in the rostral cingulate or rACC region of the brain was involved in turning on or off the fear response in the amygdala -- the almond-shaped brain centre where emotional responses to fear are processed.

"People are exposed to an ever-increasing amount of stimuli in our everyday lives, and so we realised that the brain must employ a processing mechanism to prioritise and refine responses -- we don't run away from every loud sound or unexpected sight," said Dr Joy Hirsch, who led the study, published in the journal Neuron.

They used a test called the Stroop test to try to activate whatever region must be involved.

The Stroop test measures mental flexibility by forcing people to choose between a word's meaning and its colour. For instance, someone may be asked to read a list of words such as "red", "yellow", or "green" in which the word "red" might be written in blue ink, "yellow" in pink ink and so on.

People usually respond more quickly if the colour and word match.

Hirsch's team adapted this test, using photographs of fearful and happy faces, with "FEAR" or "HAPPY" written across the images. They gave the test to 19 healthy volunteers and ran the brain scan at the same time.

The rostral cingulate seemed to light up just before the amygdala was activated, they reported.

For instance, the amygdala activated at first if FEAR was written across a happy face, and then the rostral cingulate would activate, apparently as the image of the smiling face registered, after which the amygdala would calm down, they said.

But the amygdala stayed activated for longer, and the rostral cingulate stayed unlit longer, if a fearful face also carried the "FEAR" label.

Hirsch said it is important to have a circuit to control the fear response.

Some patients with anxiety disorders and depression may eventually be helped by the findings, said Dr Eric Kandel, a Howard Hughes Medical Institute senior investigator and professor in brain sciences who worked on the paper.

"For example, if someone with anxiety has a disturbed functioning of part of the amygdala or a disturbed functioning of rostral cingulate control mechanism, and treatment could be based on the individual's specific problem," Kandel said.

- REUTERS