Burning mouth syndrome （BMS） is classified into chronic primary orofacial pain. Chronic primary pain syndrome is characterized by nociplastic pain in which pain arises from altered nociception despite no clear evidence of actual or threatened tissue damage causing the activation of peripheral nociceptors or evidence for disease or lesion of the somatosensory system causing the pain. Historically, these types of pain have been regarded as psychogenic pain. Recent studies have revealed that chronic primary pain syndrome including BMS shows dysfunction of the pain modulatory system, especially descending pain inhibition. This altered brain function can be monitored by neurophysiologic tests including quantitative sensory testing and conditioned pain modulation （CPM） in combination with imaging modalities. These research modalities have revealed that the brain in BMS patients shows temporal summation of activity in areas associated with pain modulation during tonic noxious hot stimulation of the lower lip and temporal suppression of activity in these areas by repeated noxious stimuli without perceptional pain habituation. Further, there are reports in the literature of facilitated pain response to heat and our experimental data have revealed the lack of CPM in BMS patients. The results of previous studies have suggested that dysfunction in the dopaminergic neural system is involved in altered pain modulating function.