HTR1A and myalgic encephalomeyelitis/chronic fatigue syndrome: The brain serotonin hyperactivity of ME/CFS patients was observed from neuroimaging PET data showing reduced levels of the serotonin transporter (a 5-HT reuptake molecule) in the anterior cingulate area [12] and the 5-HT1A receptor (a negative feedback loop) in multiple brain regions [11].