Excitation, inhibition, local oscillations, or large-scale loops: what causes the symptoms of schizophrenia?

What causes the positive, negative, and cognitive symptoms of schizophrenia? The importance of circuits is underscored by the finding that no single gene contributes strongly to the disease. Thus, some circuit abnormality to which many proteins can contribute is the likely cause. There are several major hypotheses regarding the circuitry involved: first, a change in the balance of excitation/inhibition in the prefrontal cortex (PFC); second, abnormal EEG oscillations in the gamma range; third, an increase in theta/delta EEG power related to changes in the thalamus (particularly midline nuclei); fourth, hyperactivity in the hippocampus and consequent dopamine hyperfunction; and fifth, deficits in corollary discharge. Evidence for these hypotheses will be reviewed.