Fear of injection is a significant factor for those who avoid dental treatment. Emotion is a major component in how we perceive pain. Particularly of interest to dental professionals are the emotions associated with local anesthesia injections. In anatomy, we learn the limbic system, prefrontal cortex and anterior cingulate gyrus control emotion. A 1991 study in the Journal of Neuropsychiatry, Neuropsychology and Behavior Neurology, found cancer patients with these areas of the brain removed perceived pain differently.