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Psychiatry is a medical subspecialty dealing with mental and behavioral disorders. Mental illness refers to diseases of the brain, because the mind is a function of the brain, and illness is a synonym for disease. Psychiatric illnesses are generally differentiated from neurological illnesses in that neurological disorders tend to have demonstrable anatomical or physiological abnormalities associated with them. Although the biological basis of psychiatric disorders is well established, the neurochemical and neuroanatomical abnormalities associated with these disorders tend to be subtle. Recent advances in brain imaging and molecular genetics provide optimism regarding our ability to understand psychiatric illnesses on a more biological and molecular basis. However, at this time, psychiatric diagnoses remain clinical and descriptive. That is to say, they are based on observation regarding symptoms, complications, and outcome. The basis of psychiatric diagnosis continues to be the psychiatric interview and mental status examination. At this time, there are no laboratory or imaging tests to diagnose mental illnesses, though laboratory tests may be helpful in diagnosing medical conditions with psychiatric symptoms, such as thyroid disease. [ABSTRACT FROM AUTHOR]

The article provides information on the development of Positron Emission Tomography (PET) in measuring detectable changes in brain function. PET generates an image of the distribution of a radioactively-labelled tracer substance that is distributed in the brain according to its pattern of physiological activity. Its use to delineate the mechanisms of disordered cerebral function is an important contribution to the investigation of geriatric disorders.

The article discusses issues related to onset of psychiatric illness and epidemiology of early-onset and late onset of illness. Major depressive disorder, bipolar disorder and schizophrenia are some of the mental disorder that best-characterize DSM-IV. Studies on prevalence and correlates of early onset versus late-onset disorders are unreliable for methodological reasons that provoke all psychiatric and retrospective studies.

The article presents a study on the diagnostic test required to clarify the aetiology and identity of treatable cases including neuro-imaging in comparison with other test in all patients having reversible cause for dementia. The treatment for dementia has transferred the classification of productive cost from investigation to treatment.

The article provides information on the neuro-imaging techniques in the study of depression. The use of neuro-imaging techniques has provided a major advance in the elucidation of its functional neuro-anatomy, metabolic correlates and biochemistry. These techniques have also advanced our knowledge of the pathophysiology and chemical pathology of depression with the introduction of single-photon emission computed tomography, positron emission tomography, and magnetic resonance spectroscopy.