Phobias are among the most common psychiatric disorders, affecting more than 10 percent of us at some point in our lives. Fear is part of human nature—it's the emotion that keeps us safe in a dangerous world. Thanks to the survival value of fear, natural selection has given us brain circuits dedicated to detecting danger and avoiding harm—an alarm system that gets wired up early in life. But sometimes our fears uncouple from realistic threats . They can become excessive and irrational, causing us to feel terror and avoid things when we don’t really need to. When irrational fears start to interfere with our lives, they move into the realm of a phobia.
The most common phobias have to do with objects and situations that were the greatest threats to our evolutionary ancestors: animals, heights, enclosed spaces, strangers (see here for a list of the top 10 phobias). We’re probably all biologically predisposed to pick up these fears, but some of us—by virtue of our particular set of genes and experiences—are more vulnerable to develop phobias.
The good news is that phobias are perhaps the most easily treated mental disorders. In fact, they can be eliminated—that is, cured—by a type of psychotherapy known as behavior therapy. Behavior therapy for phobias involves a systematic process of exposing and desensitizing someone to their worst fear. And the cure can sometimes be achieved in a single session of treatment.
We know a good deal about the brain circuits involved in developing and overcoming phobias. Three regions of the brain’s emotional circuitry, in particular, are crucial to how we learn to fear and how we can learn not to. The amygdala is the brain’s fear hub, a sentry for detecting threats. The prefrontal cortex helps modulate fear learning in the amygdala and is a key player in overcoming or “extinguishing” fears. And the hippocampus, part of the temporal lobe, processes the context of the threat and also helps us remember the fear experience. Extinguishing fears involves learning that the thing we fear is actually not a threat—and that’s how behavior therapy works its magic.
In a new study1, researchers at Northwestern University, used fMRI to ask what happens in the brain when behavior therapy cures a phobia. They studied 12 adults with spider phobia (aka arachnophobia). Before treatment, the subjects were brain scanned while they looked at two types of pictures: spiders (the phobic stimulus) and moths (the neutral stimulus).
As we’d expect, fMRI scans showed brain regions involved in fear–including the amygdala and prefrontal cortex—had a much stronger response to the spider photos. Then they had a single session of behavior therapy that involved having them gradually approach and then touch a live tarantula.
In less than three hours, all 12 were successfully treated. When the fMRI scans were repeated at the end of treatment, the fear regions’ excessive response to spiders was gone. But another region—the dorsolateral prefrontal cortex (DLPFC)--was now more active.
(see the figure). That’s interesting because the DLPFC is thought to be important for “cognitive reappraisal”—that is, reframing things in a more rational light. When the subjects were scanned again at six months, the fear regions were still quieted, but the researchers saw something else intriguing. Activity in the visual cortex, which is responsible for processing visual images, was correlated with improvement in spider phobia. In other words, a longer-term cure of their phobia may have helped the subjects literally see spiders as less threatening.
The study has its limitations, including a relatively small sample size, but it fits with a larger body of research that is teaching us how experience, including psychotherapy, changes the brain.
1. Hauner KK, Mineka S, Voss JL, Paller KA. Exposure therapy triggers lasting reorganization of neural fear processing. Proceedings of the National Academy of Sciences of the United States of America. 2012; 109(23): 9203-8.