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Pleasantness slips mind of schizophrenics

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CHICAGO — Schizophrenics react strongly to unpleasant odors but often do not appreciate pleasant ones, and their brains' response to smells may provide a clue to their paranoid thoughts, researchers said this week.

When schizophrenics in the study were exposed to an unpleasant odor emitted by a type of acid, brain scans showed an increase in blood flow to their prefrontal cortex, a region normally used to recognize pleasant stimuli.

The prefrontal cortex was apparently "hijacked" in the brains of schizophrenics to detect a potential threat and was not available to respond when they sniffed a pleasant lemon odor, according to a study by researchers at the University of Iowa Hospitals and Clinics in Iowa City.

"The use of . . . (the) prefrontal cortex for such survival tasks may also lead to an aberrant tendency to attribute threatening aspects to stimuli and in turn give rise to paranoid thinking," lead researcher Benedicto Crespo-Facorro wrote in this week's issue of the Journal of the American Medical Association.

A healthy brain used the centrally located limbic regions to react to and evaluate threats, but patients with schizophrenia had decreased blood flow to three key limbic regions in response to the unpleasant odor, the study said.

While previous research on brain activity in schizophrenics has focused on hallucinations and memory deficits, the University of Iowa study focused on their perception of pleasant and unpleasant sensory experiences.

Schizophrenics' inability to experience pleasurable emotions, a common symptom, is called anhedonia.

"Patients with schizophrenia appear to have a normal ability to experience unpleasant emotions, coupled with an impairment in the ability to experience pleasant ones, and the more psychotic they are, the greater the acuity of their ability to recognize unpleasantness," the study said.