Dopamine D2 densities and the schizophrenic brain

Meta-analytic methods were used to test the D2 dopamine density hypothesis in schizophrenia. Post-mortem as well as in-vivo (i.e., PET and SPECT) neuroimaging studies that met criteria for inclusion into the meta-analysis were gathered from 1980 to 1996. The mean effect size across studies corresponds to an effect size of 1.47 (d). Although large, the effect size obtained does not meet heuristic benchmark criteria that would suggest D2 density increases to be a marker for schizophrenia. That is, roughly 30% of patients with schizophrenia could not be discriminated from normal healthy controls. Based on the findings, it is argued that D2 density receptor increases in patients with schizophrenia, although a reliable finding in many patients (i.e., approximately 70%), is not a specific or consistent marker for schizophrenia.