The revised dopamine hypothesis suggests hyperactive dopamine activity and transmission in the mesolimbic area and hypoactive activity in the prefrontal cortex of schizophrenic patients. Dopamine dysregulation is also observed in other various brain regions (amygdala and prefrontal cortex), which are valuable for processing emotions. Positron emission tomography studies have found differences in dopamine contents in those regions for patients with schizophrenia. The dopamine system in the hippocampus tends to be overactive in these patients.