[Neuroimaging in schizophrenia]

This overview is focused on functional neuroimaging including functional magnetic resonance imaging (fMRI), positron emission tomography (PET) and single photon emission computed tomography (SPECT). Recent evidence for the "dopamine hypothesis of schizophrenia" is summarized including alterations of presynaptic dopamine metabolism and postsynaptic receptor binding potential. Emphasis is given to dopaminergic challenge studies using amphetamine and AMPT. Several PET and SPECT studies have shown a pronounced increase of amphetamine-induced dopamine release as well as decrease of AMPT-induced dopamine depletion in drug-naive schizophrenic patients, indicating a dysregulation of dopaminergic neurotransmission. Results of studies combining amphetamine challenge and the NMDA receptor antagonist ketamine are related to glutaminergic dysfunction and neurotransmitter interactions. FMRI and PET results demonstrating alterations in task-specific functional connectivity between brain areas are discussed with a focus on the prefrontal cortex and temporal structures. Increase of serotonin-1A receptor binding potential in prefrontal and mesotemporal cortex is related to the serotonin-dopamine interaction. Genetic neuroimaging techniques, including voxel-based morphometry (VBM) and fMRI, revealing significant effects of the dopamine metabolizing enzyme COMT on functional activation in prefrontal areas are also discussed. Functional neuroimaging based on challenge-paradigms in PET as well as task-specific state- or trait-dependent alterations of activation patterns in fMRI, seems to be a promising candidate for the development of biological marker tests for schizophrenia.