Neural mechanisms of anhedonia in schizophrenia - A PET study of response to unpleasant and pleasant odors

Context Loss of the capacity to experience pleasure (anhedonia) is a core c linical feature of schizophrenia. Although functional imaging techniques ha ve been successful in identifying the neural basis of cognitive impairments in schizophrenia, no attempts to date have been made to investigate neural systems underlying emotional disturbances. Objective To study the neural basis of emotional processing in schizophreni a by exploring the pattern of brain responses to olfactory stimuli in patie nts and healthy volunteers. Design Positron emission tomographic study of patients with schizophrenia a nd healthy volunteers, Positron emission tomographic data were collected be tween July 21, 1995, and September 11, 1997, and data analyses were conduct ed in 1999-2001. Setting The Mental Health Clinical Research Center at the University of Iow a, Iowa City. Participants Sixteen healthy volunteers with a mean age of 29.5; years and 18 patients with schizophrenia and a mean age of 30.0 years. Main Outcome Measure Areas of relative increase or decrease in regional cer ebral blood flow, measured using positron emission tomography and the [O-15 ]water method while participants performed an emotion-induction olfactory t ask to determine response to pleasant (vanillin) and unpleasant (4-methylva leric acid) odors, compared between patients and healthy volunteers. Results Patients with schizophrenia subjectively experienced unpleasant odo rs in a manner similar to healthy volunteers but showed impairment in the e xperience of pleasant odors. The analysis of the regional cerebral blood fl ow revealed that patients failed to activate limbic/paralimbic regions (eg, insular cortex, nucleus accumbens, and parahippocampal gyrus) during the e xperience of unpleasant odors, recruiting a compensatory set of frontal cor tical regions instead. Conclusion Abnormalities in the complex functional interactions between mes olimbic and frontal regions may underlie emotional disturbances in schizoph renia.