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11 October 2012
Fear is a normal response to some aspects of life. It is healthy to fear middle-aged men in lederhosen. Fear is also a rational response to American evangelists who preach from horseback. It is also normal to experience mild to moderate levels of fear at the thought of Bruce Willis’ skull. In short, fear is an appropriate response to the threatening or the bizarre. Yet with time we can learn that certain things need not fill us with dread and that, for instance, Bruce Willis’ head poses no immediate danger. Yet new research shows that this capacity to make unwarranted fear disappear is exactly what teenage brains lack.
The new research comes in two parts; the first on mice and the second on humans.
In the mice portion of their research it was found that the normal brain mechanisms to eradicate fear do not operate in adolescent mice. They found that the prelimbic region in the prefrontal cortex is triggered during fear acquisition. When the fear is rationalised however, the infralimbic prefrontal cortex works to eliminate this fear. However, the studies found that neurons from the infralimbic prefrontal cortex are not active in adolescent mice whereas they are active in both younger and older mice.
This begged the question as to whether adolescent humans would also have a reduced capacity to extinguish fear.
To examine this the researchers had children, teenagers, and adults take part in a test wherein they wore earphones and had metres attached to them to measure their sweat. They then looked at computer monitors that showed a series of yellow and blue squares. Half of the time a blue square would be accompanied by an unpleasant noise. Increased sweat meant that the subjects had developed a fear of the noise and were associating seeing the blue square with the noise.
On the next day the subjects did the same test but this time the blue square was not associated with the noise.
Teenagers did not decrease their fear response as measured by sweat. By contrast, the children and adults did decrease their fear response quite quickly. So the teenagers showed a reduced capacity or fear extinction.
If teenagers have difficulty, at the neuronal level, in learning that something which once frightened them is no longer frightening this may explain, at least in part, the anxieties that accompany adolescence and offer avenues for understanding as well as possible routes for treatment.