People's brains react to a photograph of a frightened face, even when it is flashed on a screen too quickly to be consciously recognised.
Researchers at Columbia University in New York have found responses to subliminal images in the amygdala, the part of the brain associated with emotional responses, as
well as the attention and vision regions of the cerebral cortex.
"What we think we've identified is a circuit in the brain that's responsible for enhancing the processing of unconsciously detected threats in anxious people," said Amit Etkin, who led the study. "Our study shows that there's a very important role for unconscious emotions in anxiety."
Writing in the journal Neuron, the researchers said they used high-resolution functional magnetic resonance imaging, a way of scanning brain activity in real time, on 17 undergraduates.
While the volunteers were looking at a computer, the researchers displayed a fearful face on the monitor for 33 milliseconds, immediately followed by a neutral face.
The frightened face appeared and disappeared so quickly the volunteers could have had no conscious awareness of it.
The 17 volunteers had normal variations in anxiety.
But the more anxious a student was naturally, the more of a reaction was seen in the brain to a frightened face, the researchers found.
When the students looked at the scared faces long enough for conscious recognition, a different brain circuit was used. That activity did not vary according to the underlying level of anxiety.
"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," said Joy Hirsch, who worked on the study.
"Our findings now demonstrate a biological basis for that unconscious emotional vigilance."
She said it might be possible to use fMRI imaging to test new drugs to treat anxiety and to check a patient's response to therapy or medications.
- REUTERS
