Using single-photon emission computed tomography; Dutch researchers were able to detect biochemical differences in the brains of individuals with generalized social anxiety disorder (social phobia), providing evidence of a long-suspected biological cause for the dysfunction. Reported in the Journal of Nuclear Medicine, the study compared densities of elements of the serotonin and dopamine neurotransmitter systems in the brains of 12 people diagnosed with social anxiety disorder, but who had not taken medication to treat it, and a control group of 12 healthy people.
The researchers used a radioactive compound that binds with elements of the brain's serotonin and dopamine systems. It revealed functional alterations in the thalamus, midbrain and in the striatum (known to be acted upon by dopamine). The altered uptake activity in these regions indicated a greater level of disordered function.
"Our study provides direct evidence for the involvement of the brain's dopaminergic system in social anxiety disorder in patients who had no prior exposure to medication," said Dr. van der Wee, from the Leiden University Medical Center. "It demonstrates that social anxiety has a physical, brain dependent component."
Other neuroimaging studies have shown abnormalities in glucose and oxygen consumption in the brain, according to van der Wee, who also points to causality as an additional issue. "Most of the people involved in these earlier studies were known to be already suffering from the disorder, so we do not know if the abnormalities were present before the onset of the disorder," he said.
Based on earlier studies, some researchers have suggested that social anxiety disorder is a result of the interplay between a genetic or acquired biological vulnerability and environment. More recent research has indicated that social anxiety disorder might be related to an imbalance of the neurotransmitter serotonin. This is the first time the brain's dopaminergic system was examined directly.
"Although there are no direct implications for treatment as a result of this study yet, it is another piece of evidence showing biological abnormalities, which may lead to new therapeutic approaches and insight into the origins of the disorder," said Dr. van der Wee.
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Source: Journal of Nuclear Medicine
