Limiting phobia exposure length may help brain process fears

In patients with phobias, exposure to phobic images without conscious awareness is more effective than longer, conscious exposure for reducing fear, according to researchers, who recently published their results in Human Brain Mapping.

The study was led by Bradley S. Peterson, MD, director of the Institute for the Developing Mind at Children’s Hospital Los Angeles, and Paul Siegel, PhD, associate professor of psychology at Purchase College of the State University of New York.

Investigators used fMRI to determine whether certain areas of the brain involved in fear processing were more strongly activated by unconscious exposure.

“Although we expected—and observed—activation of the neural regions that process fear, we also found activation in regions that regulate the emotional and behavioral responses to fear—reducing the conscious experience of fear,” said Dr. Peterson, who is also professor of pediatrics and psychiatry at the Keck School of Medicine of the University of Southern California.

A “phobia” is often defined as an irrational fear, but there is an evolutionary basis for many of the stimuli that produce phobic responses. For this study, investigators used spiders—a common cause of phobic responses.

Forty-two young adult women were chosen for the study—21 were arachnophobic, and 21 were not. Previous research has shown that 75% to 80% of people who experience phobias are women.

The participants were exposed to images under three conditions:

• Very brief exposure to masked images of spiders
• Clearly visible exposure to images of spiders
• Masked images of flowers (control images)

The images were backward masked, a technique in which a target image is shown very briefly and is then immediately followed by a non-target image (mask) that prevents recognition of the target.

In phobic individuals, very brief exposure to spider images strongly activated the subcortical regions of the brain involved in immediate fear processing. The participants did not experience conscious fear, possibly because the short exposure time activated brain regions that regulate fear.

Clearly visible exposure to the spider images deactivated the areas of the brain that regulate fear responses and induced the conscious experience of fear.

“Counterintuitively, our study showed that the brain is better able to process feared stimuli when [the stimuli] are presented without conscious awareness,” said Dr. Siegel. “Our findings suggest that phobic people may be better prepared to face their fears if at first they are not consciously aware that they have faced them.”

Dr. Peterson added that this technique offers the potential to treat children and adolescents with anxiety disorders. Current theories are based on directly confronting feared stimulus, which can cause significant emotional distress in some patients.