Amit Etkin, Joy Hirsch, Eric Kandel and colleagues at the Columbia University College of Physicians and Surgeons that a specific region of the amygdala shows greater activation in unconscious processing of threats for people with higher levels of basic anxiety.
The researchers said that their experimental technique not only pinpoints an important structure involved in the neural circuitry of processing fearful stimuli, but also offers a way to measure the success of therapies for anxiety disorders.
The researchers concentrated on the amygdala because the almond-shaped structure in the depths of the brain is known to encode the emotional content of memories. The amygdala's influence on such encoding determines, for example, how indelibly the memory of a trauma is imprinted on the brain.
In their studies, the researchers showed volunteer subjects images of fearful faces, while the volunteers' brains were being scanned using functional magnetic resonance imaging (fMRI). The sight of fearful faces has been shown in many studies to trigger a fearful response in people. In the commonly used brain imaging technique of fMRI, harmless magnetic fields and radio signals are used to measure blood flow in brain regions, which reflects brain activity.
In their experiments, the researchers first asked the volunteers to fill out a questionnaire that determined their basic level of anxiety. They then told the volunteers only that they were to identify the color of the faces they would see.