Researchers at Columbia University Medical Center have found that fleeting images of fearful faces – images that appear and disappear so quickly that they escape conscious awareness – produce unconscious anxiety that can be detected in the brain with the latest neuroimaging machines.
It's one of the first times that neuroimaging has captured the brain's processing of unconscious emotion.
Using a high-resolution version of functional magnetic resonance imaging (fMRI) the researchers observed a structure in the brain important for emotional processing - the amygdala - lights up with activity when people unconsciously detected the fearful faces.
Although the study was conducted in people who had no anxiety disorders, the researchers says that the findings should also apply to people with anxiety disorders.
"Psychologists have suggested that people with anxiety disorders are very sensitive to subliminal threats and are picking up stimuli the rest of us do not perceive," says Dr. Joy Hirsch, professor of neuroradiology and psychology and director of the fMRI Research Center at Columbia University Medical Center, where the study was conducted. "Our findings now demonstrate a biological basis for that unconscious emotional vigilance."
Dr. Hirsch adds that the finding makes a profound prediction: "If a treatment for anxiety works, we should see the unconscious activity in the input end of the amygdala go down. In future studies, we want to use brain imaging to test the effectiveness of psychotherapeutic and pharmacological treatments for anxiety disorders."
The study was led by Drs. Hirsch; Eric Kandel, Senior Investigator at the Howard Hughes Institute, and Director of the Kavli Institute for Brain Science at Columbia University Medical Center; Rene Hen, professor of pharmacology; and graduate students Amit Etkin and Kristen Klemenhagen. Their research appears in the Dec. 16 issue of Neuron.
About the study
In the study, the researchers presented images of fearful facial expressions, which are powerful signals of danger in all cultures, to 17 different subjects. None of the 17 volunteers had any anxiety disorders, but their underlying anxiety varied from the 6th to the 85th percentile of undergraduate norms, as measured by a well-validated questionnaire.
"These are the type of normal differences that would be apparent if these people got stuck in an elevator," Dr. Hirsch says. "Some of them would go to sleep; some would climb the walls."
While the subjects were looking at a computer, the researchers displayed an image of a fearful face onto the monitor for 33 milliseconds, immediately followed by a similar neutral face. The fearful face appeared and disappeared so quickly that the subjects had no conscious awareness of it.
But the fMRI scans clearly revealed that the brain had registered the face and reacted, even though the subjects denied seeing it. These scans show that the unconsciously perceived face activates the input end of the amygdala, along with regions in the cortex that are involved with attention and vision.
Brain activity varies with level of anxiety
The researchers also noticed that the amount of brain activity varied from person to person, depending on their scores on the anxiety quiz.
The amygdalas of anxious people was far more active than the amygdalas of less anxious people. And anxious subjects showed more activity in the attention and vision regions of the cortex, which manifested itself in faster and more accurate answers when the subjects were asked questions about the neutral face.
"What we think we've identified is a circuit in the brain that's reponsible for enhancing the processing of unconsciously detected threats in anxious people," says Amit Etkin, the study's first author. "An anxious person devotes more attention and visual processing to analyze the threat. A less anxious person uses the circuit to a lesser degree because they don't perceive the face as much as a threat."
Unconscious vs. conscious processing of fearful faces
In contrast to unconscious processing of fearful faces, the researchers found that when subjects looked at the fearful faces for 200 milliseconds, long enough for conscious recognition, a completely different brain circuit was used to process the information. And the activity in that circuit did not vary according to the subject's level of anxiety.
"Our study shows that there's a very important role for unconscious emotions in anxiety," Etkin says.
Source: Eurekalert & othersLast reviewed: By John M. Grohol, Psy.D. on 21 Feb 2009
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