Low levels of serotonin in the brain are seen as a possible cause of depression and many antidepressants act by blocking a protein that transports serotonin away from the nerve cells. A brain imaging study at Karolinska Institutet now shows that the average level of the serotonin transporter increased in a group of 17 individuals who recovered from depression after cognitive behavioral therapy. The results are published in the journal Translational Psychiatry.