Is the odour identification deficit in schizophrenia influenced by odour hedonics?

Pleasant and unpleasant odor identification ability is associated with distinct dimensions of negative symptoms transdiagnostically in psychotic disorders

Negative symptoms are among the greatest sources of functional impairment for individuals with schizophrenia, yet their mechanisms remain poorly understood. Olfactory impairment is associated with negative symptoms. The processing of pleasant olfactory stimuli is subserved by reward-related neural circuitry while unpleasant olfactory processing is subserved by emotion-related neural circuitry, suggesting that these two odor dimensions may offer a window into differential mechanisms of negative symptoms. We examined whether pleasant and unpleasant odor identification bears differential relationships with avolition and inexpressivity dimensions of negative symptoms, whether these relationships are transdiagnostic, and whether pleasant and unpleasant odor processing also relate differently to other domains of functioning in a sample of individuals diagnosed with schizophrenia (N = 54), other psychotic disorders (N = 65), and never-psychotic adults (N = 160). Hierarchical regressions showed that pleasant odor identification was uniquely associated with avolition, while unpleasant odor identification was uniquely associated with inexpressivity. These relationships were largely transdiagnostic across groups. Additionally, pleasant and unpleasant odor identification displayed signs of specificity with other functional and cognitive measures. These results align with past work suggesting dissociable pathomechanisms of negative symptoms and provide a potential avenue for future work using valence-specific olfactory dysfunction as a semi-objective and low-cost marker for understanding and predicting the severity of specific negative symptom profiles.

Olfactory dysfunction in frontotemporal dementia and psychiatric disorders: A systematic review

Frontotemporal dementia (FTD) is a progressive neurodegenerative disease. Diagnosis of FTD, especially the behavioural variant, is challenging because of symptomatic overlap with psychiatric disorders (depression, schizophrenia, bipolar disorder). Olfactory dysfunction is common in both FTD and psychiatric disorders, and often appears years before symptom onset. This systematic review analysed 74 studies on olfactory function in FTD, depression, schizophrenia and bipolar disorder to identify differences in olfactory dysfunction profiles, focusing on the most common smell measures: odour identification and discrimination. Results revealed that FTD patients were severely impaired in odour identification but not discrimination; in contrast, patients diagnosed with schizophrenia showed impairments in both measures, while those diagnosed with depression showed no olfactory impairments. Findings in bipolar disorder were mixed. Therefore, testing odour identification and discrimination differentiates FTD from depression and schizophrenia, but not from bipolar disorder. Given the high prevalence of odour identification impairments in FTD, and that smell dysfunction predicts neurodegeneration in other diseases, olfactory testing seems a promising avenue towards improving diagnosis between FTD and psychiatric disorders.

Sex differences in hedonic judgement of odors in schizophrenia cases and healthy controls

The neurocircuitries subserving affective and olfactory processes overlap, are sexually dimorphic, and show disruptions in schizophrenia, suggesting their intersection may be a window on the core process producing psychosis. This study investigated diagnostic and sex differences in hedonic judgments of odors and smell identification in 26 schizophrenia cases and 27 healthy controls. Associations between olfaction measures and psychiatric symptoms were also examined. Cases and controls had similar identification accuracy of unpleasant odors, but cases were significantly less accurate in naming pleasant odors. In cases, greater negative symptom severity was related to abnormal hedonic judgments; specifically, higher pleasantness ratings for unpleasant odors and higher unpleasantness ratings for pleasant odors. Greater positive symptom severity was associated with lower pleasantness ratings for neutral odors. Regarding sex differences, male cases and female controls rated pleasant odors as significantly more unpleasant than male controls. Correlations between depression severity and pleasantness ratings of neutral odors were in opposite directions in male and female cases. These results suggest that a normal sexual dimorphism in the circuitry for hedonic odor judgments may interact with schizophrenia pathology, supporting the utility of olfactory hedonics as a sex-specific biomarker of this pathology.

Olfactory processing in bipolar disorder, major depression, and anxiety

OBJECTIVES

Although olfactory abnormalities are well established in schizophrenia, considerably less work has examined olfactory performance in other neuropsychiatric conditions. In the current study, we examined odor identification, odor discrimination, detection threshold, and odor hedonic processing performance in individuals with bipolar I disorder (n = 43; n = 13 with psychotic features), bipolar II disorder (n = 48), major depressive disorder (MDD) (n = 134), anxiety (n = 48), and no mental disorder (n = 72) who participated in a community-based family study.

METHODS

Best estimate DSM-IV diagnoses were based on in-depth personal interviews as well as interviews with family members. Olfactory tests were administered during an in-person clinical visit and were compared using robust linear regression adjusting for age, sex, and psychiatric medication use, as well as nicotine use when necessary.

RESULTS

Compared to controls, odor identification performance was lower among individuals with MDD (b = -1.37, 95% confidence interval [CI]: -2.50, -0.24) and bipolar I disorder (b = -1.79, 95% CI: -3.51, -0.67). Among the latter group, performance was only reduced among those with psychotic features (b = -3.49, 95% CI: -6.33, -0.65), particularly for pleasant odors (b = -1.46, 95% CI: -2.51, -0.42). Those with MDD showed lower identification accuracy for neutral odors (b = -0.63, 95% CI: -1.20, -0.06). Performances on measures of odor discrimination and detection threshold did not differ by diagnostic group.

CONCLUSIONS

Collectively, these findings indicate that odor identification difficulties may exist in mood disorders, especially when psychotic features are present. In contrast, the global olfactory dysfunction observed in schizophrenia may not be a feature of other neuropsychiatric conditions.

Deficits in the identification of pleasant odors predict the transition of an at-risk mental state to psychosis

OBJECTIVE

Existing knowledge of the relationship between olfactory identification (OI) ability and clinical risk of psychosis is inconsistent. To address this inconsistency, the aim of the present study was to identify the relationship between OI ability, with regard to the hedonic attributes of odors, and the risk of transition to psychosis in individuals with an ARMS.

METHODS

A group of 81 individuals meeting the ARMS criteria according to the Comprehensive Assessment of At Risk Mental State were at baseline administered with the University of Pennsylvania Smell Identification Test. The hedonic attributes of odorants were normatively established. Participants were followed up for transition to psychosis for a mean period of 36.1months (SD:27.5months).

RESULTS

The presence of deficits in the identification of pleasant odors was found to be a risk factor for conversion from an ARMS to schizophrenia. The hazard ratio for each point in deficit scores in the Cox regression model was 1.455 (95% CI: 1.211-1.747), p<0.0001. Significant deficits in the identification of pleasant odors were associated with a risk for conversion at both early and late time points from baseline.

CONCLUSIONS

The findings imply that the impaired identification of pleasant odorants may be a risk factor for the transition of an ARMS into a psychotic disorder, and highlights the need for further research of OI in "at-risk" cohorts, taking into account the hedonic attributes of odors.

Olfactory identification in patients with schizophrenia - the influence of β-endorphin and calcitonin gene-related peptide concentrations

BACKGROUND

The relationship between the olfactory system and emotional processing is an area of growing interest in schizophrenia research. Both the orbitofrontal cortex and amygdala are involved in the processing of olfactory information, and olfactory deficits may be also influenced by endogenous opioids and calcitonin gene-related peptide (CGRP), which is probably involved in dopaminergic transmission. However, the relationship between endorphins and dopaminergic transmission has not been fully explored.

METHODS

Odor identification performance and valence interaction was evaluated among 50 schizophrenic patients and 50 controls. Schizophrenia symptoms were assessed using the Positive and Negative Syndrome Scale (PANSS). All study participants were subjected to the University of Pennsylvania Smell Identification Test (UPSIT), blood β-endorphin (BE) and CGRP measurement.

RESULTS

Insignificantly higher BE concentrations were observed in the patient group, while significantly higher UPSIT scores were seen in controls (mean UPSIT 32.48 vs 26.82). The patients demonstrated significantly more identification errors for pleasant (P=0.000) and neutral (P=0.055) odors than for unpleasant odors. Patients with higher BE concentrations made more identification errors concerning pleasant (R_s=-0.292; P=0.04) and neutral odors (R_s=-0.331; P=0.019). Although the concentration of CGRP was significantly higher in the patient sample (P<0.001), no relationship was observed between concentration and UPSIT performance. A strong negative correlation was observed between PANSS N score and UPSIT total score (R_s=-0.646; P=0.000), between PANSS N score and identification by valence for pleasant and neutral odors (UPSIT n/16: R_s=-0.450, P=0.001; UPSIT n/15: R_s=-0.586, P=0.000), and a weak negative correlation between PANSS N score and identification of unpleasant odors (UPSIT n/9: R_s=-0.325, P=0.021).

CONCLUSIONS

Schizophrenic patients present a unique pattern of smell identification characterized by aberrant hedonic ratings for pleasant odors but not unpleasant ones. Individuals with predominant negative symptoms and higher BE concentrations are most able to identify negative odors.

The effect of odor valence on olfactory performance in schizophrenia patients, unaffected relatives and at-risk youth

Given the presence of odor identification impairment in individuals with schizophrenia and recent evidence of aberrant odor hedonic processing, the aim of this investigation was to examine the influence of valence and intensity on odor identification in schizophrenia patients, their first-degree family members, and young persons at clinical risk for psychosis. Participants completed the 16-item Sniffin' Stick Odor Identification Test. A logistic regression was conducted to assess the influence of valence and intensity on odor identification accuracy. Identification performance in the schizophrenia patients and youths at clinical risk for psychosis was significantly influenced by odor valence, but not intensity. Identification accuracy in first-degree family members was not influenced by valence or intensity. These data suggest that abnormalities in odor valence perception may represent an environmentally-mediated marker for hedonic disturbance that could have predictive utility in future conversion to psychosis. Further research examining the utility of odor valence measures as markers for psychosis risk is warranted.

Effects of adjunctive intranasal oxytocin on olfactory identification and clinical symptoms in schizophrenia: results from a randomized double blind placebo controlled pilot study

BACKGROUND

Deficits in olfactory identification have been widely reported in patients with schizophrenia (SZ) and are associated with negative symptomatology. Adjunctive oxytocin delivered intranasally has been shown to improve some aspects of social cognition as well as positive and negative symptoms in patients with schizophrenia. Given the intranasal delivery route of oxytocin to olfactory pathways and that olfactory abnormalities are a potential endophenotype in SZ, we investigated the effect of intranasal oxytocin on olfactory identification as well as positive and negative symptoms in people with schizophrenia.

METHODS

Individuals with schizophrenia or schizoaffective disorder (n=28; 16 outpatients, 12 inpatients) were randomized to receive adjunctive intranasal oxytocin 20 IU BID or placebo for 3 weeks.

RESULTS

All 28 participants completed the clinical trial. Odor identification performance significantly improved on the University of Pennsylvania Smell Identification Test (UPSIT) total score and subscore for pleasant smells. UPSIT score (F=5.20, df=1,23, p=0.032) and subscore for pleasant smells (F=4.56, df=1,23, p=0.044), in patients treated with oxytocin were compared to placebo from baseline to endpoint. Global symptomatology as well as positive and negative symptoms were not improved by intranasal oxytocin. In fact, global symptoms, not positive or negative symptoms, improved in the placebo group. Secondary analysis shows that intranasal oxytocin improved negative symptoms in the small group of inpatients. Intranasal oxytocin was well tolerated during the three week trial.

CONCLUSION

Adjunctive intranasal oxytocin may improve olfactory identification, particularly in items of positive valence. Larger studies are needed to determine the effects of oxytocin on negative symptoms in SZ. (NCT00884897; http://www.clinicaltrials.gov).