A handful of studies have assessed changes in brain neurotransmission following psychotherapy, showing increases in serotonin markers after treatment in patients with MDD [88, 89], a relationship between reductions in symptoms of social phobia and changes in D2-R binding following cognitive behavioural therapy (CBT) [90] and reduced serotonin 1B receptor (5HT1B-R) binding after CBT in patients with MDD [91]. This evidence concerns the gene HTR1B and major depressive disorder.