18 October 2018

Freeze or flee? Psychologists identify brain region that evokes flight response

You’re crossing the street, when suddenly a car comes rushing at you. What do you do? There are two possible reactions: either you freeze, or you get out of the way. Passive or active fear, in other words. Utrecht University experimental psychologists David Terburg and Jack van Honk, along with researchers from the universities of Cape Town and Lausanne, have discovered which area of the brain prevents the passive fear response, allowing you (hopefully in time) to dodge the oncoming car: the basolateral amygdala. Their findings have been published in the leading scientific journal Cell.

From an evolutionary perspective, passive fear is older than active fear. Terburg: ‘Passive fear, or freezing, is a primal instinct. Reptiles still do it: they often remain completely motionless when faced with danger.’ Mammals that appeared later in the evolutionary process have the basolateral amygdala which can suppress this reptilian response.

Unpleasant shock

For their study, the UU researchers used test subjects who had suffered damage to their basolateral amygdala. A healthy control group also took part. ‘Both groups sat in front of a computer. Pictures then appeared on the screen, and the participants were instructed to push a button within a certain amount of time: a sort of “flight” response, essentially. If they didn’t do this in time, they were given a small, unpleasant shock.’ In contrast to the healthy control group, the test subjects with brain damage exhibited more passive fear responses. This was observed both in their behaviour and in the activation of their brain stem. ‘Because the functioning of their basolateral amygdala is impaired, it is also harder for them to suppress their passive fear.’

This finding is relevant for people with anxiety disorders

Panic disorder

In the second part of their study, Terburg and Van Honk tried to find a solution. ‘Rats with damage to the brain region in question were similarly unable to flee from danger. But after we administered an oxytocin agonist, their flight response seemed to be restored.’
This finding is relevant for people with anxiety disorders. ‘Someone suffering from panic disorder, for instance, will start to hyperventilate when faced with stress. We aren’t quite there yet, but it’s not hard to imagine that this type of oxytocin agonist could prevent such intense anxious reactions.’

Read Terburg's article on the website of Cell.

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