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Abstract

Prior research has revealed that olfactory identification ability is impaired in male patients with schizophrenia. Additionally, lateralized differences have been observed in olfactory functioning in normal individuals who have intact sense of smell. The purpose of this study was to determine whether the pattern of olfactory laterality observed in male patients with schizophrenia was different from that observed in non-schizophrenic, normal, male control subjects. In addition, if patients with unirhinal olfactory identification deficits were found, did these individuals have a different profile of neuropsychological impairment relative to those patients with intact sense of smell? Methods: Forty-three male in-patients with a DSM-IV diagnosis of schizophrenia and 59 normal male control subjects were assessed unirhinally on three measures of olfactory function: olfactory acuity, identification and discrimination ability. Additionally, a battery of neuropsychological tests sensitive to brain lesions in regions critical to olfaction (left and right temporal and frontal lobes) was also administered. Results: No particular pattern of olfactory laterality was observed in either the normal control or the male patient groups on any of the olfactory measures. Using cutting scores generated from performance of the normal control subjects on the olfactory identification task, patients were classified according to nostril deficit. Three groups were compared: left microsmic (n=12), right microsmic (n=5) and normosmic schizophrenic controls (n=25). On tests of left hemisphere function, the left microsmic group was preferentially impaired while on tests of right hemisphere function, the right microsmic group was preferentially impaired. On demographic and experiential variables, the left microsmic group was impaired on a measure of premorbid IQ (reading of irregular words) and the normosmic group was significantly younger than both other groups. Discussion and implications . These data suggest that using a simple, non-invasive measure of unirhinal olfactory identification ability, male patients with schizophrenia could be categorized into subgroups with lateralized brain dysfunction. Those with left hemisphere abnormalities may be those with a neurodevelopmental form of the disorder given their poor reading capacity (an ability which is acquired early in life) despite similarities amongst subgroups on educational achievement and parental socioeconomic status.