Another patient I saw in consultation recently, a 23-year-old woman, described how she became anxious when she was younger after seeing a commercial about asthma. “It made me incredibly worried for no reason, and I had a panic attack soon after seeing it,” she said. As an older teenager, she became worried about getting too close to homeless people and would hold her breath when near them, knowing that “this was crazy and made no sense.”

B. J. Casey, a professor of psychology and the director of the Sackler Institute at Weill Cornell Medical College, has studied fear learning in a group of children, adolescents and adults. Subjects were shown a colored square at the same time that they were exposed to an aversive noise. The colored square, previously a neutral stimulus, became associated with an unpleasant sound and elicited a fear response similar to that elicited by the sound. What Dr. Casey and her colleagues found was that there were no differences between the subjects in the acquisition of fear conditioning.

But when Dr. Casey trained the subjects to essentially unlearn the association between the colored square and the noise — a process called fear extinction — something very different happened. With fear extinction, subjects are repeatedly shown the colored square in the absence of the noise. Now the square, also known as the conditioned stimulus, loses its ability to elicit a fear response. Dr. Casey discovered that adolescents had a much harder time “unlearning” the link between the colored square and the noise than children or adults did.

IN effect, adolescents had trouble learning that a cue that was previously linked to something aversive was now neutral and “safe.” If you consider that adolescence is a time of exploration when young people develop greater autonomy, an enhanced capacity for fear and a more tenacious memory for threatening situations are adaptive and would confer survival advantage. In fact, the developmental gap between the amygdala and the prefrontal cortex that is described in humans has been found across mammalian species, suggesting that this is an evolutionary advantage. This new understanding about the neurodevelopmental basis of adolescent anxiety has important implications, too, in how we should treat anxiety disorders. One of the most widely used and empirically supported treatments for anxiety disorders is cognitive behavior therapy, a form of extinction learning in which a stimulus that is experienced as frightening is repeatedly presented in a nonthreatening environment. If, for example, you had a fear of spiders, you would be gradually exposed to them in a setting where there were no dire consequences and you would slowly lose your arachnophobia. The paradox is that adolescents are at increased risk of anxiety disorders in part because of their impaired ability to successfully extinguish fear associations, yet they may be the least responsive to desensitization treatments like cognitive behavior therapy precisely because of this impairment.

This presents a huge clinical challenge since young people are generally risk takers who are more prone to exposure to trauma as a direct result of their behavior, to say nothing of those who were exposed to the horrors of the wars in Iraq and Afghanistan or the mass shootings like those in Newtown and Aurora. Many of them will go on to develop post-traumatic stress disorder, which is essentially a form of fear learning. Now we have good reason to think that exposure therapy alone may not be the best treatment for them. A recent study of children and adolescents with anxiety disorders found that only 55 to 60 percent of subjects responded to either cognitive behavior therapy or an antidepressant alone, but 81 percent responded to a combination of these treatments. And in another study, there was preliminary evidence that adolescents responded less well to cognitive behavior therapy than children or adults.

This isn’t to say that cognitive therapy is ineffective for teenagers, but that because of their relative difficulty in learning to be unafraid, it may not be the most effective treatment when used on its own.

And there is potentially something else to worry about with our anxious adolescents: the meteoric rise in their use of psychostimulants like Ritalin and Adderall. In theory, stimulants could have a negative impact on the normal developmental trajectory of anxious teenagers.