The neural basis of olfactory function and its relationship with anhedonia in individuals with schizotypy: An exploratory study

Olfactory functional covariance connectivity in Parkinson's disease: Evidence from a Chinese population

Introduction

Central anosmia is a potential marker of the prodrome and progression of Parkinson's disease (PD). Resting-state functional magnetic resonance imaging studies have shown that olfactory dysfunction is related to abnormal changes in central olfactory-related structures in patients with early PD.

Methods

This study, which was conducted at Guanyun People's Hospital, analyzed the resting-state functional magnetic resonance data using the functional covariance connection strength method to decode the functional connectivity between the white-gray matter in a Chinese population comprising 14 patients with PD and 13 controls.

Results

The following correlations were observed in patients with PD: specific gray matter areas related to smell (i.e., the brainstem, right cerebellum, right temporal fusiform cortex, bilateral superior temporal gyrus, right Insula, left frontal pole and right superior parietal lobule) had abnormal connections with white matter fiber bundles (i.e., the left posterior thalamic radiation, bilateral posterior corona radiata, bilateral superior corona radiata and right superior longitudinal fasciculus); the connection between the brainstem [region of interest (ROI) 1] and right cerebellum (ROI2) showed a strong correlation. Right posterior corona radiation (ROI11) showed a strong correlation with part 2 of the Unified Parkinson's Disease Rating Scale, and right superior longitudinal fasciculus (ROI14) showed a strong correlation with parts 1, 2, and 3 of the Unified Parkinson's Disease Rating Scale and Hoehn and Yahr Scale.

Discussion

The characteristics of olfactory-related brain networks can be potentially used as neuroimaging biomarkers for characterizing PD states. In the future, dynamic testing of olfactory function may help improve the accuracy and specificity of olfactory dysfunction in the diagnosis of neurodegenerative diseases.

Odor Identification Ability as a Mediator of Schizotypal Traits and Odor Hedonic Capacity in Non-Clinical Children and Adolescents

Background: Previous studies have investigated the relationship between schizotypal traits and odor identification ability as well as the relationship between schizotypal traits and odor hedonic capacity in adults. However, very little is known about the relationship among these three factors, especially in children and adolescents. The current study aimed to explore the relationship among these three factors in children and adolescents as well as the potential role of odor identification ability. Method: A total of 355 non-clinical children and adolescents (aged 9−16 years) were recruited in the study. They were asked to complete the Universal Sniff Test (U-Sniff), the Chemosensory Pleasure Scale for Children (CPS-C), and the Schizotypal Personality Questionnaire—Child (SPQ-C). Results: The SPQ-C scores were negatively correlated with both the odor identification scores and the odor hedonic scores (p = 0.022 and p < 0.001, respectively). Only the interpersonal−affective factor of the SPQ-C was negatively correlated with the odor identification scores (p = 0.031). The odor identification scores were significantly positively associated with the odor hedonic scores (p < 0.001). Moreover, the relationship between odor hedonic capacity and schizotypal traits, especially the interpersonal−affective factor, was mediated by odor identification ability. Conclusions: Schizotypal traits were negatively correlated with both odor identification ability and odor hedonic capacity in children and adolescents, while odor identification ability was found to mediate the relationship between odor hedonic capacity and schizotypal traits, especially the interpersonal−affective factor. Our study indicated that improving odor identification ability through olfactory training may have a positive influence on odor hedonic capacity in individuals with schizotypal traits.

Functional Covariance Connectivity of Gray and White Matter in Olfactory-Related Brain Regions in Parkinson’s Disease

Before the onset of motor symptoms, Parkinson’s disease (PD) involves dysfunction of the anterior olfactory nucleus and olfactory bulb, causing olfactory disturbance, commonly resulting in hyposmia in the early stages of PD. Accumulating evidence has shown that blood oxygen level dependent (BOLD) signals in white matter are altered by olfactory disorders and related stimuli, and the signal changes in brain white matter pathways show a certain degree of specificity, which can reflect changes of early olfactory dysfunction in Parkinson’s disease. In this study, we apply the functional covariance connectivity (FCC) method to decode FCC of gray and white matter in olfactory-related brain regions in Parkinson’s disease. Our results show that the dorsolateral prefrontal, anterior entorhinal cortex and fronto-orbital cortices in the gray matter have abnormal connectivity with the posterior corona radiata and superior corona radiata in white matter in patients with Parkinson’s hyposmia. The functional covariance connection strength (FCS) of the right dorsolateral prefrontal cortex and white matter, and the covariance connection strength of the left superior corona radiata and gray matter function have potential diagnostic value. These results demonstrate that alterations in FCC of gray and white matter in olfactory-related brain regions can reflect the change of olfactory function in the early stages of Parkinson’s disease, indicating that it could be a potential neuroimaging marker for early diagnosis.

Electrical stimulation of the trigeminal nerve improves olfaction in healthy individuals: A randomized, double-blind, sham-controlled trial

BACKGROUND

Both activated by environmental odorants, there is a clear role for the intranasal trigeminal and olfactory nerves in smell function. Unfortunately, our ability to perceive odorants decreases with age or with injury, and limited interventions are available to treat smell loss.

OBJECTIVE

We investigated whether electrical stimulation of the trigeminal nerve via trigeminal nerve stimulation (TNS) or transcranial direct current stimulation (tDCS) modulates odor sensitivity in healthy individuals.

METHODS

We recruited 20 healthy adults (12 Female, mean age = 27) to participate in this three-visit, randomized, double-blind, sham-controlled trial. Participants were randomized to receive one of three stimulation modalities (TNS, tDCS, or sham) during each of their visits. Odor detection thresholds were obtained at baseline, immediately post-intervention, and 30-min post-intervention. Furthermore, participants were asked to complete a sustained attention task and mood assessments before odor detection testing.

RESULTS

Findings reveal a timeXcondition interaction for guaiacol (GUA) odorant detection thresholds (F (3.188, 60.57) = 3.833, P = 0.0125), but not phenyl ethyl alcohol (PEA) odorant thresholds. At 30-min post-stimulation, both active TNS and active tDCS showed significantly increased sensitivity to GUA compared to sham TNS (Sham TNS = -8.30% vs. Active TNS = 9.11%, mean difference 17.43%, 95% CI 5.674 to 29.18, p = 0.0044; Sham TNS = -8.30% vs. Active tDCS = 13.58%, mean difference 21.89%, 95% CI 10.47 to 33.32, p = 0.0004).

CONCLUSION

TNS is a safe, simple, noninvasive method for boosting olfaction. Future studies should investigate the use of TNS on smell function across different stimulation parameters, odorants, and patient populations.

Odour identification impairment is a trait but not a disease-specific marker for bipolar disorders: Comparisons of bipolar disorder with different episodes, major depressive disorder and schizophrenia

OBJECTIVE

Olfactory deficits have been reported in bipolar disorder, but this finding is controversial. This study investigated whether olfactory deficit can serve as a specific marker for bipolar disorder by comparing olfactory function in different mood episodes of bipolar disorder. We also compared olfactory function in bipolar disorder and other mental disorders - namely, major depressive disorder and schizophrenia.

METHODS

The study consisted of two experiments. Experiment 1 enrolled 175 bipolar disorder patients (70 depressed subgroup, 70 manic subgroup and 35 euthymic subgroup) and 47 controls. Experiment 2 enrolled the participants from Experiment 1, along with 85 major depressive disorder and 90 schizophrenia patients. The Sniffin' Sticks test was used to evaluate odour identification ability and odour threshold (as a measure of odour sensitivity). The Hamilton Depression Rating Scale and Young Mania Rating Scale were used to assess depressive symptoms in all subjects and manic symptoms in bipolar disorder patients, respectively. We also used the Positive and Negative Syndrome Scale to assess clinical symptoms in schizophrenia patients.

RESULTS

All three bipolar disorder patient subgroups (depressed, manic and euthymic subgroup) showed reduced odour identification ability compared to controls; however, only patients in the acute phase of a mood episode (depressed, and manic subgroup) showed impaired odour sensitivity. Clinical symptoms were negatively correlated with odour sensitivity but not odour identification ability. Bipolar disorder and major depressive disorder patients showed less odour identification and sensitivity impairment than schizophrenia patients.

CONCLUSION

Odour sensitivity is a potential dopaminergic marker for distinguishing between bipolar disorder patients in acute phase vs remission, while odour identification is a trait but a nonspecific marker of bipolar disorder.

Schizotypy, childhood trauma and brain morphometry

BACKGROUND

Childhood trauma confers risk for psychosis and is associated with increased 'schizotypy' (a multi-dimensional construct reflecting risk for psychosis in the general population). Structural brain alterations are associated with both childhood trauma and schizotypy, but the potential role of trauma exposure in moderating associations between schizotypy and brain morphology has yet to be determined.

METHODS

Participants were 160 healthy individuals (mean age: 40.08 years, SD = 13.64, range 18-64; 52.5% female). Childhood trauma exposure was assessed using the Childhood Adversity Questionnaire, and schizotypy was assessed using the Schizotypal Personality Questionnaire. Univariate voxel-based morphometry and multivariate analyses of grey matter volume covariation (GMC; derived from independent component analysis) were performed to determine the main effects of schizotypy, trauma exposure and their interaction on these indices of grey matter volume. Moderation analyses were performed following significant interaction.

RESULTS

Levels of schizotypy, in particular the Cognitive-Perceptual and Interpersonal dimensions, were negatively associated with GMC in the striatum, the hippocampus/parahippocampal gyrus, thalamus and insulae. Trauma exposure was negatively associated with GMC of the middle frontal gyrus and parietal lobule, while negatively associated with GMC in the cerebellum. Levels of schizotypy (total scores, and the cognitive-perceptual dimension) were negatively associated with striatal GMC in individuals not exposed to trauma, but not in those exposed to trauma.

CONCLUSIONS

Schizotypy and childhood trauma were independently associated with changes of grey matter in brain regions critical for cognition and social cognition. In individuals not exposed to trauma, increased schizotypy was associated with decreased striatal and limbic grey matter.

Altered activation and functional connectivity in individuals with social anhedonia when envisioning positive future episodes

BACKGROUND

Anticipatory pleasure deficits are closely correlated with negative symptoms in schizophrenia, and may be found in both clinical and subclinical populations along the psychosis continuum. Prospection, which is an important component of anticipatory pleasure, is impaired in individuals with social anhedonia (SocAnh). In this study, we examined the neural correlates of envisioning positive future events in individuals with SocAnh.

METHODS

Forty-nine individuals with SocAnh and 33 matched controls were recruited to undergo functional MRI scanning, during which they were instructed to simulate positive or neutral future episodes according to cue words. Two stages of prospection were distinguished: construction and elaboration.

RESULTS

Reduced activation at the caudate and the precuneus when prospecting positive (v. neutral) future events was observed in individuals with SocAnh. Furthermore, compared with controls, increased functional connectivity between the caudate and the inferior occipital gyrus during positive (v. neutral) prospection was found in individuals with SocAnh. Both groups exhibited a similar pattern of brain activation for the construction v. elaboration contrast, regardless of the emotional context.

CONCLUSIONS

Our results provide further evidence on the neural mechanism of anticipatory pleasure deficits in subclinical individuals with SocAnh and suggest that altered cortico-striatal circuit may play a role in anticipatory pleasure deficits in these individuals.

Developmental Trajectories of Cortical Thickness in Relation to Schizotypy During Adolescence

Investigating potential gray matter differences in adolescents presenting higher levels of schizotypy personality traits could bring further insights into the development of schizophrenia spectrum disorders. Research has yet to examine the morphological correlates of schizotypy features during adolescence prospectively, and no information is available on the developmental trajectories from adolescence to adulthood. We employed mixed model regression analysis to investigate developmental trajectories of cortical thickness (CT) in relation to schizotypy dimensions in a cohort of 109 adolescents from the general population for whom MRI-scans were acquired over a 5-year period, culminating in a total of 271 scans. Structural data were processed with FreeSurfer software, statistical analyses were conducted using mixed regression models following a ROI-based approach, and schizotypy was assessed with the Schizotypal Personality Questionnaire (SPQ). Accelerated thinning was observed in the posterior cingulate cortex in relation to high levels of positive schizotypy, whereas high levels of disorganized schizotypy were associated with a similar trajectory pattern in the anterior cingulate cortex. The developmental course of CT in the prefrontal, occipital, and cingulate cortices differed between adolescents expressing higher vs lower levels of negative schizotypy. Participants reporting high scores on all schizotypy dimensions were associated with differential trajectories of CT in posterior cingulate cortex and occipital cortex. Consistently with prospective developmental studies of clinical risk conversion, the negative schizotypy dimension appears to constitute the most informative dimension for psychosis-related psychopathology, as its cerebral correlates in adolescents most closely overlap with results found in clinical high risk for psychosis studies.

The Mediating Effect of Alexithymia on the Relationship Between Schizotypal Traits and Sleep Problems Among College Students

A body of research has investigated the relationship between alexithymia and sleep problems, as well as the relationship between schizophrenia and alexithymia. However, there have been few studies on the relationships between the three. The current study explored the relationship between schizotypal traits and sleep problems among college students, and the potential role of alexithymia as a mediator of this relationship. The participants were all first-year students at a medical university in Guangdong province, China. A total of 2,626 college students participated. They were asked to complete a questionnaire that incorporated the Schizotypal Personality Questionnaire (SPQ), the Toronto Alexithymia Scale (TAS-20), and the Insomnia Severity Index (ISI). The results revealed a relatively high percentage of students with mild insomnia (74.8%) and a smaller percentage with moderate to severe insomnia (7.9%). Correlation analysis revealed that both the TAS-20 and ISI scores had significant positive correlations with the SPQ score (p < 0.01). There was also a significant positive correlation between the TAS-20 and ISI scores (p < 0.01). The ISI score was significantly influenced by the SPQ score in a direct way, and increased considerably with increases in the TAS-20 score, indicating the importance of alexithymia as a mediator. The mediation model was tested via regression analysis and the bias-corrected bootstrap method, and these results further confirmed the role of alexithymia as a mediator.

Early-Onset Schizophrenia Showed Similar but More Severe Olfactory Identification Impairment Than Adult-Onset Schizophrenia

BACKGROUND

"Early-onset schizophrenia" (EOS) is defined as disease with onset before the age of 18 years. This subset of schizophrenia exhibits worse cognitive function and carries a worse prognosis than adult-onset schizophrenia (AOS). Olfactory impairment has been found in patients with schizophrenia-spectrum disorders. However, most research has focused on olfactory impairment in patients with AOS: olfactory function in EOS is not known. The aim of this study was to investigate the olfactory identification ability in EOS, and its relationship with negative symptoms.

METHODS

We compared olfactory function between two independent samples: 40 patients with EOS and 40 age- and sex-matched healthy controls (HCs); as well as 40 patients with AOS and 40 age- and sex-matched HCs. The University of Pennsylvania Smell Identification Test was administered.

RESULTS

The EOS group and AOS group exhibited worse olfactory identification ability than HCs; impairment correlated significantly with negative symptoms. Olfactory identification was worse in patients suffering EOS compared with those suffering AOS.

CONCLUSION

Olfactory identification impairment may be a trait marker of schizophrenia.

Chemosensory Anhedonia in Patients With Schizophrenia and Individuals With Schizotypy: A Questionnaire Study

Anhedonia, the loss or decline of the ability to enjoy pleasure, is an important clinical characteristic of schizophrenia. Schizotypal traits refer to the appearance of subclinical symptoms of schizophrenia across normal people. Still, few studies have investigated chemosensory anhedonia in schizophrenia patients and schizotypy individuals. Seventy-one schizophrenia patients (SCZ), 162 schizotypy individuals (SCT) as selected by the Schizotypal Personality Questionnaire (SPQ), and 182 healthy controls (HC) participated in our study. We used the Positive and Negative Syndrome Scale (PANSS) to measure the clinical symptoms of schizophrenia patients. All participants completed the Chemosensory Pleasure Scale (CPS), which was used to assess participants' smell and taste hedonic capacities. We found that the three groups differed in chemosensory anhedonia. The SCZ group presented more severe chemosensory anhedonia than the SCT group, and the SCT group presented more severe chemosensory anhedonia than the HC group. We also found that chemosensory hedonic capacity was negatively correlated with negative schizotypal traits in the SCT group. Our results suggested that chemosensory anhedonia is an important characteristic of schizophrenia spectrum disorders.

Olfactory threshold selectively predicts positive psychometric schizotypy

Olfactory impairment might be useful as a non-invasive pre-morbid biological marker of psychosis. People with schizophrenia show consistent impairments, but an association between olfaction and schizotypy in non-clinical populations is inconclusive and has been somewhat controversial. This is important as impairment in patients may be artefacts of antipsychotic medication. Meta-analyses indicate small effect sizes in non-clinical populations, suggesting prior negative studies may have been underpowered to demonstrate them. We measured olfaction and psychometrically-defined schizotypy in a sample of 739 non-clinical volunteers [mean age 23.1]. Subsets reported whether they had a history of mental illness in the family or smoked. We used (sniffin' sticks) to measure threshold detection, discrimination and identification of odours. O-LIFE was used to measure schizotypy. Lower olfactory-threshold selectively predicted higher scores on the positive dimension, unusual experiences. This association was most evident in sub-groups reporting history of mental illness in the family and/or smoking. There was a weak trend for an association between identification and introvertive anhedonia and discrimination and cognitive disorganisation in those with a history of mental illness in the family. These data support the idea that olfaction merits further investigation as a biomarker for psychosis and that olfactory-threshold detection in particular has potential to selectively predict unusual experiences. Variability in previous studies may have been exacerbated by including different proportions of participants with history of mental illness in the family and/or smoking. We propose that non-clinical participants be stratified by these factors in future studies of olfaction and potentially any study that measures psychometric schizotypy.

Olfactory and cognitive functions in Chinese individuals at clinical high risk for psychosis

The abnormal olfactory function has been regarded as a sign in psychosis. To confirm the theory that olfactory and cognitive functions are deficient in Chinese cohort with clinical high risk state of psychosis, 19 individuals at clinical high risk for psychosis (CHRs) and 37 healthy controls (HCs) were recruited. The CHRs scored significantly lower than the HCs in the olfactory identification test and all other cognitive tests. Our findings suggest that olfactory dysfunction may be an early change of psychosis.

Olfactory identification deficit and its relationship with hedonic traits in patients with first-episode schizophrenia and individuals with schizotypy

OBJECTIVE

Olfactory identification impairments have been consistently found in schizophrenia patients. However, few previous studies have investigated this in first-episode patients. There are also inconsistent findings regarding olfactory identification ability in psychometrically-defined schizotypy individuals. In this study, we directly compared the olfactory identification ability of first-episode schizophrenia patients with schizotypy individuals. The relationship between olfactory identification impairments and hedonic traits was also examined.

METHODS

Thirty-five first-episode schizophrenia patients, 40 schizotypy individuals as defined by the Chapman's Anhedonia Scales and 40 demographically matched controls were recruited. The University of Pennsylvania Smell Identification Test was administered. Hedonic capacity was assessed using the Temporal Experience of Pleasure Scale (TEPS).

RESULTS

The results showed that both the schizophrenia and schizotypy groups showed poorer olfactory identification ability than controls, and the impairment was significantly correlated with reduced pleasure experiences.

CONCLUSION

Our findings support olfactory identification impairment as a trait marker for schizophrenia.

Motivation deficits in individuals with social anhedonia

Patients with schizophrenia have been reported to exhibit anhedonia, a reduced hedonic capacity and deficits in motivation for reward pursuit. However, it is unclear whether these deficits also exist in at-risk individuals prone to psychosis or not. The present study compared 26 individuals with social anhedonia and 28 healthy controls using a grip Effort-based Pleasure Experience Task (E-PET). The findings showed that individuals with social anhedonia did not increase their hard task choices with the elevation of reward magnitude and probability while healthy controls did. Higher reward probability and magnitude did not lead to more anticipatory pleasure in individuals with social anhedonia. The mean anticipatory pleasure experience ratings in individuals with social anhedonia were significantly lower than controls. Our results suggest that individuals with social anhedonia already exhibit motivational deficits during reward pursuit.

Olfactory function in neuropsychiatric disorders

Recent clinical studies have identified olfactory dysfunction in patients with neuropsychiatric disorders. Although these studies showed differences in olfactory function between healthy individuals and neuropsychiatric patients, no studies have compared the differences in olfactory function among neuropsychiatric disorders. The aim of the present study was to investigate olfactory function among various neuropsychiatric disorders. Three-hundred and eighteen outpatients diagnosed according to the ICD-10 code participated in the study. Olfactory function was assessed using the Open Essence test. The differences in olfactory function among disorders were compared by analyses of (co-)variance. As expected, olfactory function was significantly affected by the age and marginally affected by the gender. We investigated the differences in olfactory function among patients with different neuropsychiatric disorders (F0-F9). Olfactory function significantly differed among the diagnostic groups. Post hoc analysis showed that patients with F0 had decreased olfactory function compared to patients from the other diagnostic groups. In particular, patients with Alzheimer's disease (AD) had significantly poorer olfactory function compared to patients with other neuropsychiatric disorders. There were no differences among the other groups. These findings suggest that patients with AD had poorer olfactory function compared not only to healthy subjects but also to patients with several other neuropsychiatric disorders.

Brain fingerprints of olfaction: a novel structural method for assessing olfactory cortical networks in health and disease

Olfactory deficits are a common (often prodromal) symptom of neurodegenerative or psychiatric disorders. As such, olfaction could have great potential as an early biomarker of disease, for example using neuroimaging to investigate the breakdown of structural connectivity profile of the primary olfactory networks. We investigated the suitability for this purpose in two existing neuroimaging maps of olfactory networks. We found problems with both existing neuroimaging maps in terms of their structural connectivity to known secondary olfactory networks. Based on these findings, we were able to merge the existing maps to a new template map of olfactory networks with connections to all key secondary olfactory networks. We introduce a new method that combines diffusion tensor imaging with probabilistic tractography and pattern recognition techniques. This method can obtain comprehensive and reliable fingerprints of the structural connectivity underlying the neural processing of olfactory stimuli in normosmic adults. Combining the novel proposed method for structural fingerprinting with the template map of olfactory networks has great potential to be used for future neuroimaging investigations of olfactory function in disease. With time, the proposed method may even come to serve as structural biomarker for early detection of disease.

What does the nose know? Olfactory function predicts social network size in human

Olfaction is an important medium of social communication in humans. However, it is not known whether olfactory function is associated with social network size. This study aimed to explore the underlying neural mechanism between olfactory function and social network. Thirty-one healthy individuals participated in this study. Social network size was estimated using the Social Network Index. Olfactory function was assessed with the Sniffin' Stick Test. The results showed that there is a significant positive correlation between the size of an individual's social network and their olfactory sensitivity. We also found that amygdala functional connectivity with the orbitofrontal cortex appeared to be related to olfactory sensitivity and social network size.

Association of schizophrenia with the rs821633 polymorphism in the DISC1 gene among Han Chinese

BACKGROUND

Previous studies report that various single nucleotide polymorphisms (SNP) in the Disrupted-in Schizophrenia 1 (DISC1) gene are closely associated with schizophrenia, but there are no studies that assess the relationship of age of onset of schizophrenia with these SNPs.

OBJECTIVE

Investigate the relationship between the rs821633 SNP in the DISC1 gene and the occurrence and age of onset of schizophrenia in Han Chinese.

METHODS

We used the TaqMan genotyping technology to examine the rs821633 SNP in the DISC1 gene among 315 individuals who developed schizophrenia prior to 19 years of age ('early-onset'), 407 individuals who developed schizophrenia when 19 years of age or older ('late-onset'), and 482 healthy controls. We used survival analyses to investigate the relationship between the rs821633(C) risk allele and the age of onset of schizophrenia.

RESULTS

Compared to the prevalence in healthy controls, the prevalence of the C/C genotype of rs821633 and of the C allele in rs821633 were significantly greater in individuals with early-onset schizophrenia (X (2)=7.17, df=1, p=0.007; X (2)=7.20, df=2, p=0.032) and significantly greater in individuals with late-onset schizophrenia (X (2)=5.36, df=1, p=0.022; X (2)=6.58, df=2, p=0.041). However, there were no significant differences in the prevalence of the C/C genotype or the C allele between individuals with early-onset and late-onset schizophrenia. Kaplan-Meier survival analyses found no significant association between the rs821633(C) risk allele and age of onset in schizophrenia.

CONCLUSION

We confirm the association of polymorphism in the rs821633 SNP in the DISC1 gene with schizophrenia among Han Chinese, but we found no association between the rs821633(C) risk allele and the age of onset in individuals with schizophrenia.