The finding reported by researchers at the Leiden University Medical Center results from a study wherein densities of elements of the serotonin and dopamine neurotransmitter systems were compared in the brains of 12 persons diagnosed with social anxiety disorder, and 12 healthy people in the control group.

The persons in the experimental group had never taken medication to treat the disorder, and the subjects in the two groups were matched by sex and age.

The researchers injected both groups with a radioactive compound that binds with elements of the brain's serotonin and dopamine systems.

The radiotracer revealed functional alterations in those systems by measuring the radioactive binding in the thalamus, midbrain and pons (known to be acted upon by serotonin) and in the striatum (known to be acted upon by dopamine).

In their study report, published in the Journal of Nuclear Medicine, the researchers revealed that the altered uptake activity in those 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 of the department of psychiatry and the Leiden Institute for Brain and Cognition.

"It demonstrates that social anxiety has a physical, brain dependent component," added the researcher.