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of psychosis. Furthermore, many psychiatric diseases have early asymptomatic or transitional phases that can last years. In the case of schizophrenia, many patients experience several pre-psychotic phases prior to full onset of symptoms. Novel biomarkers could potentially identify those individuals most likely to progress to the illness in order to target preventive or early treatment. In addition to prediction and early detection, longitudinal biomarker measures may be used to assess the trajectory of the disease process. Those biomarkers that are sensitive to changes in the trajectory caused by certain drugs could be used to identify potential responders to specific pharmacological interventions (personalized medicine).

Currently there are many potential biomarkers in development for diseases such as Alzheimer’s disease, depression and schizophrenia. In depression, measures of quantitative electroencephalogram (EEG) concordance are being investigated. Potential biochemical markers include measurement of amyloid plaques and other proteins or hormones in cerebrospinal fluid or plasma. A large body of research is also focused on the search for genetic markers of these diseases. Currently, these markers have been promising in identifying individuals who are at high risk for illness; however, many lack specificity to predict those who will progress to full symptoms among the vulnerable individuals.

Neuroimaging provides several non-invasive tools for the determination of potential psychiatric biomarkers. Structural imaging such as anatomic magnetic resonance imaging (MRI) can detect lesions and atrophy, as well as cerebrovascular disease, associated with a variety of psychiatric illnesses. Functional imaging such as positron emission tomography (PET) has been used to find distinctive patterns of glucose hypometabolism in dementia. Also, changes in brain function in response to specific cognitive tasks measured with functional MRI (fMRI) may be indicators of disease. White matter tract integrity can be measured with MRI diffusion tensor imaging and has been found to correlate with drug response in patients with depression and in early stages of schizophrenia. Another MRI technique, MR spectroscopy is useful in measuring biochemical levels in a single voxel or across the brain to assess integrity of specific metabolic pathways that may be altered in disease. These and other imaging biomarkers may be combined with complementary physiological and biochemical measures for the most sensitive and specific indicators of illness.

The safe and non-invasive nature of many of these imaging techniques such as MRI make them attractive for early and repeated screenings of large populations. However, while these neuroimaging biomarkers of psychiatric



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