Up to one million Australians suffer from social phobia at any one time, making it the most common anxiety disorder, and the third most common psychiatric disorder after depression and alcohol dependence.
People with generalised social phobia experience heightened anxiety during potential or perceived threatening social situations. They generally avoid eye contact and fear any interpersonal situation.
The research, to be published in the journal Biological Psychiatry, was conducted by an international team of researchers, including Associate Professor Pradeep Nathan from Monash University's Centre for Brain and Behaviour and the Department of Physiology.
The researchers found that the area of the brain called the amygdala becomes increasingly hyperactive when patients look at threatening, angry, disgusted or fearful faces. Further, they found that the increased response in the amygdala correlated with the patients' level of social phobia symptoms.
The amygdala is in the limbic part of the brain, which controls emotions and sends messages to the parts of the brain controlling breathing and heart rate.
Using functional magnetic resonance imaging, the researchers compared brain activity when people with generalized social phobia looked at threatening faces compared to happy or neutral faces.
Dr Nathan said the study showed that functional magnetic resonance imaging could be used to monitor activity in the amygdala and therefore predict the level of clinical symptoms in generalised social phobia patients.
"Our findings suggest that amygdala activation to interpersonal threat can be specifically linked to the severity of social anxiety symptoms of individual patients with generalised social phobia," he said. Thus, it may serve not only as a useful functional marker of disease severity, but also as a marker of the effectiveness of pharmacological and psychological treatments."
The study was done by Dr Nathan in conjunction with lead author Dr Luan Phan and Dr Daniel Fitzgerald from the University of Chicago and Dr Manuel Tancer from Wayne State University.