Objective and subjective olfaction across the schizophrenia spectrum

Much research indicates that patients with schizophrenia have impaired olfaction detection ability. However, studies of individuals with psychometrically defined schizotypy reveal mixed results-some document impairments while others do not. In addition to deficits in objective accuracy in olfaction for patients with schizophrenia, there has been an interest in subjective experience of olfaction. Unfortunately, methods of assessing accuracy and subjective hedonic olfactory evaluations in prior studies may not have been sensitive enough to detect group differences in this area. This study employed a measure of olfactory functioning featuring an expanded scoring system to assess both accuracy and subjective evaluations of pleasant and unpleasant experience. Data were collected for patients with schizophrenia, young adults with psychometrically defined schizotypy, psychiatric outpatients, and healthy controls. Results of this study indicate that both the schizophrenia and outpatient psychiatric groups showed similar levels of impaired olfaction ability; however, the schizotypy group was not impaired in olfaction detection. Interestingly, with regard to subjective hedonic evaluation, it was found that patients with schizophrenia did not differ from psychiatric outpatients, whereas individuals with schizotypy tended to rate smells as significantly less pleasant than healthy control participants. This suggests that subjective olfactory assessment is abnormal in some manner in schizotypy. It also suggests that accuracy of olfaction identification may be a characteristic of severe mental illness across severe mental illness diagnoses. The results are potentially important for understanding olfaction deficits across the mental illness spectrum.