The original dopamine hypothesis proposes the idea that schizophrenia is caused by hyperactive dopamine transmission. The positive symptoms of schizophrenia are caused by increased subcortical dopamine release, and the negative symptoms are caused by reduced dopamine (D1) receptor activation in different areas of the brain. The new revised dopamine hypothesis also suggests hyperactive dopamine transmission in mesolimbic areas and hypoactive dopamine transmission in the prefrontal cortex. Further examinations of the brain (positron emission tomography) show the variations of dopamine in various areas of the brain (hippocampus, prefrontal cortex, cingulate cortex, etc).