Impaired cognitive function in schizophrenia, once thought to be a secondary effect of the psychosis, is now seen as an enduring and core feature. It has many manifestations, but the most disruptive element is arguably a fundamental defect in the patient's ability to manipulate available information. The magnitude of the cognitive deficit in schizophrenia is considerable and remains relatively stable despite fluctuations in other symptoms. The degree of dysfunction also has a high predictive value for long-term disability. In recent years, more attention has been directed towards cognitive dysfunction in schizophrenia as a result of which assessment scales and diagnostic systems increasingly incorporate cognitive dysfunction as an independent domain. Good cognitive function depends upon the brain's ability to prioritize tasks and to switch from parallel processing to sequential processing when the processing load is excessive. This requires working executive memory. Neuroimaging and functional analyses suggest that such cognitive function relies upon unimpaired prefrontal activity. In addition, there is increasing evidence that antipsychotic drugs with 5-hydroxytryptamine (5-HT)2A -blocking activity produce better cognitive function in patients with schizophrenia than drugs with predominantly dopamine (D)2 -blocking activity (conventional neuroleptics). The development of sophisticated, computer-delivered maze tasks has shown that newer antipsychotics, such as clozapine and risperidone, differ from conventional neuroleptics in their effects on cognitive function. The prospects, therefore, are that patients treated with drugs having 5-HTM2A -blocking activity will have better cognitive function and will be better able to function in life's roles than will patients treated with conventional neuroleptics.
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