London, June 18 (IANS): The researchers have found that individuals with social phobia make too much serotonin, not too little as earlier believed.

The study by researchers at Uppsala University in Sweden was published in the journal JAMA Psychiatry.

"Serotonin can increase anxiety and not decrease it as previously often assumed," said one of the researchers, Andreas Frick.

Many people feel anxious if they have to speak in front of an audience or socialise with others.

If the anxiety becomes a disability, it may mean that the person suffers from social phobia which is a psychiatric disorder.

Social phobia is commonly medicated using SSRI compounds. These change the amount of the neurotransmitter serotonin in the brain.

Based on previous studies, it was believed that individuals with social phobia had too little serotonin and that SSRIs increased the amount of available serotonin.

For the study, researchers used a so-called PET camera and a special tracer to measure chemical signal transmission by serotonin in the brain.

They found that patients with social phobia produced too much serotonin in a part of the brain's fear centre, the amygdala.

The more serotonin produced, the more anxious the patients were in social situations.

"Not only did individuals with social phobia make more serotonin than people without such a disorder, they also pump back more serotonin."