But a new study from Uppsala University researchers shows that the situation is actually the opposite.
Individuals with social phobia in fact make too much serotonin. And the more serotonin they produce, the more anxious they are in social situations.
Many people experience anxiety when 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, a psychiatric disorder.
Social phobia is commonly medicated using selective serotonin re-uptake inhibitor (SSRI) compounds. These alter the amount of the neurotransmitter serotonin available in the brain.
Too Little Serotonin
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. In a new study in the scientific journal JAMA Psychiatry, researchers from the Department of Psychology at Uppsala University show that individuals with social phobia make too much serotonin.
The team, led by professors Mats Fredrikson and Tomas Furmark, used Positron Emission Tomography 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.
A nerve cell, which sends signals using serotonin, initially releases serotonin into the space between the nerve cells.
The nerve signal arises when serotonin attaches itself to the receptor cell. The serotonin is then released from the receptor and pumped back to the original cell.
Andreas Frick, a doctoral student at Uppsala University Department of Psychology, said:
“Not only did individuals with social phobia make more serotonin than people without such a disorder, they also pump back more serotonin. We were able to show this in another group of patients using a different tracer which itself measures the pump mechanism. We believe that this is an attempt to compensate for the excess serotonin active in transmitting signals."
The discovery is a big step forward when it comes to identifying changes in the brain’s chemical messengers in people who suffer from anxiety. Earlier research has shown that nerve activity in the amygdala is higher in people with social phobia and thus that the brain’s fear centre is over-sensitive.
The new findings indicate that a surplus of serotonin is part of the underlying reason.
Frick A, Åhs F, Engman J, et al Serotonin Synthesis and Reuptake in Social Anxiety Disorder: A Positron Emission Tomography Study JAMA Psychiatry. Published online June 17, 2015. doi:10.1001/jamapsychiatry.2015.0125
Image: RCSB Protein Data Bank. Wellcome Images