Schizophrenia is a group of heterogeneous, chronic psychotic disorders. Key symptoms include hallucinations, delusions, and abnormal experiences, such as the perception of loss of control of one's thoughts, perhaps to some outside entity. Patients lose empathy with others, become withdrawn, and demonstrate inappropriate or blunted mood. Discrimination of several subtypes of the disease represents only different patterns of symptoms with little value in relating behavior to neu-ropathology. The disorder has a strong genetic component, as demonstrated by a concordance of 40 to 50% between monozygotic twins, but no objective physiological or biochemical diagnostic tests exist.
Schizophrenic symptoms have been divided into two major categories. Positive symptoms are those that can be regarded as an abnormality or exaggeration of normal function (e.g., incoherent speech, agitation). The antipsychotic drugs are generally more effective in controlling these signs. Negative symptoms are those that indicate a loss or decrease in function, such as poverty of speech content or blunted affect. Both types of features are observable in most patients. Negative signs are considered to be more chronic and persistent and less responsive to some antipsychotic agents. Although any of these symptoms may undergo partial remission, persistent dysfunction and exacerbations are typical.
Schizophrenic patients appear to have small brains with large ventricular volumes, indicating a relative deficit of neurons. Structural and functional brain imaging studies have strongly suggested that regions of the medial temporal lobe (e.g., hippocampus) have diminished numbers of neurons and also have demonstrated the inability of individuals with schizophrenia to activate the frontal cortex and successfully execute tasks that require frontal cortical function. However, the relationship between behavioral signs, neuropathology, and a postulated functional excess of dopamine (discussed later) is unknown, and no theory of causation is conclusive.
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