For instance, because efferent serotoninergic neurons negatively modulate the levels of substance P, low and high levels of serotonin and substance P, respectively, in the fluid in the brain ventricles and surrounding the spinal cord of individuals with fibromyalgia indicate modifications in the central neurotransmissions, thus resulting in alterations in the central response to pain [6,7,8,9]. This evidence concerns the gene TAC1 and fibromyalgia.