Odor discrimination deficits in schizophrenia: association with eye movement dysfunction

Inflammation-related pathology in the olfactory epithelium: its impact on the olfactory system in psychotic disorders

Smell deficits and neurobiological changes in the olfactory bulb (OB) and olfactory epithelium (OE) have been observed in schizophrenia and related disorders. The OE is the most peripheral olfactory system located outside the cranium, and is connected with the brain via direct neuronal projections to the OB. Nevertheless, it is unknown whether and how a disturbance of the OE affects the OB in schizophrenia and related disorders. Addressing this gap would be the first step in studying the impact of OE pathology in the disease pathophysiology in the brain. In this cross-species study, we observed that chronic, local OE inflammation with a set of upregulated genes in an inducible olfactory inflammation (IOI) mouse model led to a volume reduction, layer structure changes, and alterations of neuron functionality in the OB. Furthermore, IOI model also displayed behavioral deficits relevant to negative symptoms (avolition) in parallel to smell deficits. In first episode psychosis (FEP) patients, we observed a significant alteration in immune/inflammation-related molecular signatures in olfactory neuronal cells (ONCs) enriched from biopsied OE and a significant reduction in the OB volume, compared with those of healthy controls (HC). The increased expression of immune/inflammation-related molecules in ONCs was significantly correlated to the OB volume reduction in FEP patients, but no correlation was found in HCs. Moreover, the increased expression of human orthologues of the IOI genes in ONCs was significantly correlated with the OB volume reduction in FEP, but not in HCs. Together, our study implies a potential mechanism of the OE-OB pathology in patients with psychotic disorders (schizophrenia and related disorders). We hope that this mechanism may have a cross-disease implication, including COVID-19-elicited mental conditions that include smell deficits.

Inflammation-related pathology in the olfactory epithelium: its impact on the olfactory system in psychotic disorders

Smell deficits and neurobiological changes in the olfactory bulb (OB) and olfactory epithelium (OE) have been observed in schizophrenia and related disorders. The OE is the most peripheral olfactory system located outside the cranium, and is connected with the brain via direct neuronal projections to the OB. Nevertheless, it is unknown whether and how a disturbance of the OE affects the OB in schizophrenia and related disorders. Addressing this gap would be the first step in studying the impact of OE pathology in the disease pathophysiology in the brain. In this cross-species study, we observed that chronic, local OE inflammation with a set of upregulated genes in an inducible olfactory inflammation (IOI) mouse model led to a volume reduction, layer structure changes, and alterations of neuron functionality in the OB. Furthermore, IOI model also displayed behavioral deficits relevant to negative symptoms (avolition) in parallel to smell deficits. In first episode psychosis (FEP) patients, we observed a significant alteration in immune/inflammation-related molecular signatures in olfactory neuronal cells (ONCs) enriched from biopsied OE and a significant reduction in the OB volume, compared with those of healthy controls (HC). The increased expression of immune/inflammation-related molecules in ONCs was significantly correlated to the OB volume reduction in FEP patients, but no correlation was found in HCs. Moreover, the increased expression of human orthologues of the IOI genes in ONCs was significantly correlated with the OB volume reduction in FEP, but not in HCs. Together, our study implies a potential mechanism of the OE-OB pathology in patients with psychotic disorders (schizophrenia and related disorders). We hope that this mechanism may have a cross-disease implication, including COVID-19-elicited mental conditions that include smell deficits.

Unraveling the Link between Olfactory Deficits and Neuropsychiatric Disorders

Smell loss has caught public attention during the recent COVID-19 pandemic. Research on olfactory function in health and disease gains new momentum. Smell deficits have long been recognized as an early clinical sign associated with neuropsychiatric disorders. Here we review research on the associations between olfactory deficits and neuropathological conditions, focusing on recent progress in four areas: (1) human clinical studies of the correlations between smell deficits and neuropsychiatric disorders; (2) development of olfactory mucosa-derived tissue and cell models for studying the molecular pathologic mechanisms; (3) recent findings in brain imaging studies of structural and functional connectivity changes in olfactory pathways in neuropsychiatric disorders; and (4) application of preclinical animal models to validate and extend the findings from human subjects. Together, these studies have provided strong evidence of the link between the olfactory system and neuropsychiatric disorders, highlighting the relevance of deepening our understanding of the role of the olfactory system in pathophysiological processes. Following the lead of studies reviewed here, future research in this field may open the door to the early detection of neuropsychiatric disorders, personalized treatment approaches, and potential therapeutic interventions through nasal administration techniques, such as nasal brush or nasal spray.

Brain regions associated with olfactory dysfunction in first episode psychosis patients

OBJECTIVES

Olfactory dysfunction is reproducibly reported in psychotic disorders, particularly in association with negative symptoms. The superior frontal gyrus (SFG) has been frequently studied in patients with psychotic disorders, in particular with their associations with negative symptoms. The relationship between olfactory functions and brain structure has been studied in healthy controls (HCs). Nevertheless, the studies with patients with psychotic disorders are limited. Here we report the olfactory-brain relationship in a first episode psychosis (FEP) cohort through both hypothesis-driven (centred on the SFG) and data-driven approaches.

METHODS

Using data from 88 HCs and 76 FEP patients, we evaluated the correlation between olfactory functions and structural/resting-state functional magnetic resonance imaging (MRI) data.

RESULTS

We found a significant correlation between the left SFG volume and odour discrimination in FEP patients, but not in HCs. We also observed a significant correlation between rs-fMRI connectivity involving the left SFG and odour discrimination in FEP patients, but not in HCs. The data-driven approach didn't observe any significant correlations, possibly due to insufficient statistical power.

CONCLUSION

The left SFG may be a promising brain region in the context of olfactory dysfunction and negative symptoms in FEP.

Olfactory Dysfunction in Schizophrenia: Evaluating Olfactory Abilities Across Species

Though understudied relative to perturbations in the auditory and visual domains, olfactory dysfunction is a common symptom of schizophrenia. Over the past two decades, the availability of standardized assessments to quantify human olfactory abilities, and enhance understanding of the neurophysiology supporting olfaction, has increased, enabling a more thorough characterization of these deficits. In contrast to other psychiatric conditions for which olfactory dysfunction has been observed (e.g., major depressive disorder, bipolar disorder, Alzheimer's disease), the impairments observed in schizophrenia are particularly global and profound. At this level, such deficits in olfactory abilities likely impact the enjoyment of food, detection of environmental hazards, and influence social relationships. More broadly, the study of olfactory phenotypes in schizophrenia presents new avenues for detection of those at-risk for the condition, identification of therapeutic targets for treatment development, and for the characterization of novel animal models relevant to schizophrenia and psychosis. This review will consider the olfactory performance of individuals with schizophrenia in domains for which standardized assessments are available (odor sensitivity, discrimination, identification, and memory). Paradigms available for assessing these abilities in rodents will also be discussed with the aim of facilitating translation. Thus, future studies will be able to include cross-species translation of mechanisms relevant to olfactory function and cognition, what has gone awry in the disease state, and test potential therapeutics.

Deficits in odor discrimination versus odor identification in patients with schizophrenia and negative correlations with GABAergic and DNA methyltransferase mRNAs in lymphocytes

Introduction

People with schizophrenia have been reported to show deficits in tests of olfactory function. DNA methylation and GABAergic input have been implicated in biochemical processes controlling odor in animal studies, but this has not been investigated in human studies.

Methods

In a study of measures of DNA methylation and GABAergic mRNAs in lymphocytes, we also measured odor identification and discrimination with the Sniffin' Sticks battery in 58 patients with chronic schizophrenia (CSZ) and 48 controls. mRNAs in lymphocytes were assessed by qPCR using TaqManTM probes. Cognition was assessed by the MATRICS battery (Measurement and Treatment Research to Improve Cognition in Schizophrenia) in CSZ and controls, and symptoms in CSZ were assessed by PANSS scale (Positive and Negative Symptom Scale). The relationships of odor deficits with mRNA, cognition, and symptoms were explored by correlation analysis. Variables which significantly differentiated CSZ from controls were explored by logistic regression.

Results

Overall, CSZ showed significantly (P≤.001) lower scores on odor discrimination compared to controls, with a moderate effect size, but no difference in odor identification. Deficits in odor discrimination, which has not been standardly assessed in many prior studies, strongly differentiated CSZ from controls. In logistic regression analysis, odor discrimination, but not odor identification, was a significant variable predicting schizophrenia versus control class membership. This is the first study to report relationship between odor deficits and DNA methylation and GABAergic mRNAs in blood cells of human subjects. There were negative correlations of odor identification with DNA methylation enzymes mRNAs and significant negative correlations with odor discrimination and GABAergic mRNAs. Lower odor scores were significantly associated with lower cognitive scores on the MATRICS battery in CSZ but not control subjects. In CSZ, lower odor scores were significantly associated with negative symptom scores, while higher odor identification scores were associated with PANNS Excitement factor.

Discussion

Odor discrimination was a more powerful variable than odor identification in discriminating CSZ from controls and should be used more regularly as an odor measure in studies of schizophrenia. The substantive meaning of the negative correlations of odor discrimination and GABAergic mRNA variables in peripheral lymphocytes of CSZ needs more investigation and comparison with results in neural tissue.

Perceptual pathways to hallucinogenesis

Recent advances in computational psychiatry have provided unique insights into the neural and cognitive underpinnings of psychotic symptoms. In particular, a host of new data has demonstrated the utility of computational frameworks for understanding how hallucinations might arise from alterations in typical perceptual processing. Of particular promise are models based in Bayesian inference that link hallucinatory perceptual experiences to latent states that may drive them. In this piece, we move beyond these findings to ask: how and why do these latent states arise, and how might we take advantage of heterogeneity in that process to develop precision approaches to the treatment of hallucinations? We leverage specific models of Bayesian inference to discuss components that might lead to the development of hallucinations. Using the unifying power of our model, we attempt to place disparate findings in the study of psychotic symptoms within a common framework. Finally, we suggest directions for future elaboration of these models in the service of a more refined psychiatric nosology based on predictable, testable, and ultimately treatable information processing derangements.

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.

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.

The influence of semantic processing on odor identification ability in schizophrenia

Despite the well-documented observation of odor identification deficits in schizophrenia, less is known about where the disruption in the process of correctly identifying an odor occurs. This study aimed to determine the potential moderating effects of semantic processing on the observed olfactory dysfunction in schizophrenia. Schizophrenia patients and healthy comparison subjects completed two versions of the University of Pennsylvania Smell Identification Test (UPSIT): an uncued free-response version and the standard multiple-choice paradigm, as well as three semantic measures: The Boston Naming Test, Animal Naming, and Pyramids and Palm Tree Test. Schizophrenia patients yielded significantly lower scores than the comparison group on the standard UPSIT and on semantic measures. No relationship was observed between olfactory and semantic task performance in patients. These data suggest that odor identification deficits may not be primarily due to semantic processing deficits in schizophrenia.

Olfaction, "olfiction," and the schizophrenia-spectrum: an updated meta-analysis on identification and acuity

Olfaction deficits in individuals with schizophrenia are well documented. A meta-analysis conducted nearly a dozen years ago on the topic revealed a deficit of a full standard deviation in magnitude compared to nonpatient controls. Recent efforts have been attempted to determine whether deficits in olfactory identification and acuity reflect a vulnerability marker of schizophrenia-spectrum pathology. To address this issue, the present study conducted a meta-analysis of 16 studies of individuals with schizotypy, defined in terms of a) "ultra-high risk" status, b) having an affected biological family member, or c) having extreme scores on a schizotypy questionnaire. We also conducted an updated meta-analysis of 40 studies of olfactory functioning in schizophrenia. Consistent with the prior meta-analysis, patients with schizophrenia showed impairments in olfaction identification on a full standard deviation in magnitude (d = -.99). Individuals with schizotypy showed much more subtle (d = -.24) differences in olfaction, though the effect sizes were higher for studies examining individuals at "ultra-high risk" (d = -.67) versus studies examining individuals with psychometrically-defined (d = -.14) schizotypy. Differences in olfactory acuity, relative to their respective control groups, were small for both the schizophrenia (d = -.45) and schizotypy (d = -.38) studies but were similar in magnitude. The present findings argue against the notion that deficits in olfaction identification are a vulnerability marker of schizophrenia. Suggestions for future research are recommended.

Olfactory acuity is associated with mood and function in a pilot study of stable bipolar disorder patients

OBJECTIVES

Olfactory dysfunction is described in several neuropsychiatric disorders but there is little research on olfactory processing in bipolar disorder.

METHODS

We assessed odor detection threshold (sensitivity) and smell identification test scores, along with symptoms, cognition, and social function in 20 DSM-IV bipolar disorder patients and 44 control subjects.

RESULTS

The patient and control groups had similar demographic measures, intelligence, and mean olfaction scores, but significantly differed in social domains, including adjustment, function, and anxiety. Odor detection sensitivity showed significantly opposite correlations for the depressive and manic mood domains in bipolar disorder (r to z = 2.83, p = 0.005). Depressive symptoms were related to increased sensitivity (the ability to detect odors at a lower concentration) and mania symptoms were related to decreased sensitivity for odor detection. Increased sensitivity for odor detection also predicted significantly better employment (r = -0.642, p = 0.024), whereas less sensitivity was associated with social avoidance (r = 0.702, p =0.024) and social fear (r = 0.610, p = 0.046).

CONCLUSIONS

Diminished odor detection sensitivity predicted mania and social avoidance, whereas more sensitive odor detection predicted more depressive symptoms but better employment functioning in bipolar disorder patients. Odor acuity may be an illness state marker of mood syndromes in bipolar disorder. Alternatively, differences in odor acuity may identify heterogeneous subgroups within the bipolar spectrum. Longitudinal assessments in a large, sex-stratified sample are needed to understand the implications of odor sensitivity in patients with bipolar disorder.

Paternal age related schizophrenia (PARS): Latent subgroups detected by k-means clustering analysis

BACKGROUND

Paternal age related schizophrenia (PARS) has been proposed as a subgroup of schizophrenia with distinct etiology, pathophysiology and symptoms. This study uses a k-means clustering analysis approach to generate hypotheses about differences between PARS and other cases of schizophrenia.

METHODS

We studied PARS (operationally defined as not having any family history of schizophrenia among first and second-degree relatives and fathers' age at birth ≥ 35 years) in a series of schizophrenia cases recruited from a research unit. Data were available on demographic variables, symptoms (Positive and Negative Syndrome Scale; PANSS), cognitive tests (Wechsler Adult Intelligence Scale-Revised; WAIS-R) and olfaction (University of Pennsylvania Smell Identification Test; UPSIT). We conducted a series of k-means clustering analyses to identify clusters of cases containing high concentrations of PARS.

RESULTS

Two analyses generated clusters with high concentrations of PARS cases. The first analysis (N=136; PARS=34) revealed a cluster containing 83% PARS cases, in which the patients showed a significant discrepancy between verbal and performance intelligence. The mean paternal and maternal ages were 41 and 33, respectively. The second analysis (N=123; PARS=30) revealed a cluster containing 71% PARS cases, of which 93% were females; the mean age of onset of psychosis, at 17.2, was significantly early.

CONCLUSIONS

These results strengthen the evidence that PARS cases differ from other patients with schizophrenia. Hypothesis-generating findings suggest that features of PARS may include a discrepancy between verbal and performance intelligence, and in females, an early age of onset. These findings provide a rationale for separating these phenotypes from others in future clinical, genetic and pathophysiologic studies of schizophrenia and in considering responses to treatment.

Olfactory discrimination varies in mice with different levels of α7-nicotinic acetylcholine receptor expression

Previous studies have shown that schizophrenics have decreased expression of α7-nicotinic acetylcholine (α7) receptors in the hippocampus and other brain regions, paranoid delusions, disorganized speech, deficits in auditory gating (i.e., inability to inhibit neuronal responses to repetitive auditory stimuli), and difficulties in odor discrimination and detection. Here we use mice with decreased α7 expression that also show a deficit in auditory gating to determine if these mice have similar deficits in olfaction. In the adult mouse olfactory bulb (OB), α7 expression localizes in the glomerular layer; however, the functional role of α7 is unknown. We show that inbred mouse strains (i.e., C3H and C57) with varying α7 expressions (e.g., α7 wild-type [α7+/+], α7 heterozygous knock-out [α7+/-] and α7 homozygous knock-out mice [α7-/-]) significantly differ in odor discrimination and detection of chemically-related odorant pairs. Using [(125)I] α-bungarotoxin (α-BGT) autoradiography, α7 expression was measured in the OB. As previously demonstrated, α-BGT binding was localized to the glomerular layer. Significantly more expression of α7 was observed in C57 α7+/+ mice compared to C3H α7+/+ mice. Furthermore, C57 α7+/+ mice were able to detect a significantly lower concentration of an odor in a mixture compared to C3H α7+/+ mice. Both C57 and C3H α7+/+ mice discriminated between chemically-related odorants sooner than α7+/- or α7-/- mice. These data suggest that α7-nicotinic-receptors contribute strongly to olfactory discrimination and detection in mice and may be one of the mechanisms producing olfactory dysfunction in schizophrenics.

Olfactory function and schizophrenia: an update

PURPOSE OF REVIEW

Olfaction is a field of growing interest in schizophrenia research. This article reviews recent studies on olfactory functions in schizophrenia.

RECENT FINDINGS

The current literature provides additional insights into olfactory deficits, abnormalities, and olfactory hedonic dysfunction in schizophrenia. Recent findings reinforce particular associations with negative symptoms and deficit syndrome schizophrenia. Studies indicate that abnormalities in patients with schizophrenia extend to more peripheral olfactory structures and functions, including olfactory receptor neuron dysfunction. Olfactory identification ability was found to relate to prodromal disorganization symptoms in young high-risk patients. Further support for the notion of a genetic contribution to olfactory dysfunction in schizophrenia derives from studies reporting physiological olfactory dysfunction (olfactory event-related potentials) in unaffected relatives, and an odor-specific hyposmia, present in both patients with schizophrenia and family members.

SUMMARY

Further research is needed to improve our understanding of olfactory dysfunction in schizophrenia. Recent encouraging findings underscore that the olfactory system is a field of research that holds promise for advancing our understanding of the pathophysiology of schizophrenia and possibly as a useful endophenotypic marker of neurodevelopmental vulnerability.

Scents and nonsense: olfactory dysfunction in schizophrenia

Among the sensory modalities, olfaction is most closely associated with the frontal and temporal brain regions that are implicated in schizophrenia and most intimately related to the affective and mnemonic functions that these regions subserve. Olfactory probes may therefore be ideal tools through which to assess the structural and functional integrity of the neural substrates that underlie disease-related cognitive and emotional disturbances. Perhaps more importantly, to the extent that early sensory afferents are also disrupted in schizophrenia, the olfactory system-owing to its strategic anatomic location-may be especially vulnerable to such disruption. Olfactory dysfunction may therefore be a sensitive indicator of schizophrenia pathology and may even serve as an "early warning" sign of disease vulnerability or onset. In this article, we review the evidence supporting a primary olfactory sensory disturbance in schizophrenia. Convergent data indicate that structural and functional abnormalities extend from the cortex to the most peripheral elements of the olfactory system. These reflect, in part, a genetically mediated neurodevelopmental etiology. Gross structural and functional anomalies are mirrored by cellular and molecular abnormalities that suggest decreased or faulty innervation and/or dysregulation of intracellular signaling. A unifying mechanistic hypothesis may be the epigenetic regulation of gene expression. With the opportunity to obtain olfactory neural tissue from live patients through nasal epithelial biopsy, the peripheral olfactory system offers a uniquely accessible window through which the pathophysiological antecedents and sequelae of schizophrenia may be observed. This could help to clarify underlying brain mechanisms and facilitate identification of clinically relevant biomarkers.

Olfaction: a potential cognitive marker of psychiatric disorders

Cognitive deficits are well documented in psychiatric disorders, particularly in schizophrenia and depression. Cognitive activity roots in perceptions. However, research on sensorial alterations in psychiatric conditions has mainly focused on visual or auditory processes and less on olfaction. Here, we examine data on olfactory deficits in psychiatric patients using a systematic review of recent publications. Schizophrenic patients are mainly characterized by no reliable change in odour sensitivity and by a deficit in odour identification, recognition and discrimination. Depressed patients principally exhibit a deficit in the hedonic aspects of this perception, even if, in some case, alterations in sensitivity or identification are also found. Changes in odour perception are also found in dementia and in some neurodegenerative disease, but in this case alterations concern all aspects of the sensorial experience (detection threshold, identification and recognition). Taken together, these data indicate that olfactory abnormalities might be a marker of psychiatric conditions, with a specific pattern for each disease.

Psychopathology and neuropsychological impairments in deficit and nondeficit schizophrenia of Chinese origin

Deficit schizophrenia is a relatively homogeneous subtype of patients which is considered helpful to explore the pathogenesis of schizophrenia. The aim of the present study was to reexamine the clinical characteristics of deficit (n=30) and nondeficit schizophrenia (n=93) in a Chinese sample and investigate the differences of neurocognitive function among the two subtypes of schizophrenia and the normal controls (n=103). Schizophrenia patients completed the Brief Psychiatric Rating Scale (BPRS), Scale for the Assessment of Negative Symptoms (SANS) and Scale for the Assessment of Positive Symptoms (SAPS). Additionally, all participants completed an abbreviated version of the Wechsler Adult Intelligence Scale (WAIS-RC) and a neuropsychological test battery examining the executive functions, visuospatial abilities and explicit memory related to the frontal, parietal, and temporal lobe functions. The deficit group received higher scores than the nondeficit group on the BPRS anergia factor and SANS affective flattening, alogia, avolition-apathy, anhedonia-asociality subscales, but not on the SAPS. Both two schizophrenia subgroups performed more poorly on the WAIS-RC and neuropsychological tests than the normal controls. Moreover, deficit patients performed worse than nondeficit patients on the prorated IQ, the Trail Making Test, Wisconsin Card Sorting test and Block Design test. The present study replicated symptom profiles in deficit vs. nondeficit schizophrenia in the Chinese sample. Furthermore, this study suggested that deficit schizophrenia is associated with frontal and parietal lobe impairment, and that temporal lobe dysfunction may be a common basis for cognitive impairment in schizophrenia as a whole.

No association between psychometrically-determined schizotypy and olfactory identification ability in first-degree relatives of patients with schizophrenia and non-psychiatric controls

OBJECTIVE

This study examined potential associations between schizotypy--including positive, negative, and disorganized domains--and olfactory identification ability. Based on a prior report (Park, S., Schoppe, S., 1997. Olfactory identification deficit in relation to schizotypy. Schizophr. Res. 26, 191-197), it was hypothesized that positive and negative schizotypy would be associated with poorer olfactory identification ability, at least among male participants.

METHOD

As part of a larger study, the Schizotypal Personality Questionnaire (SPQ) and University of Pennsylvania Smell Identification Test (UPSIT) were administered to 98 participants, including 44 healthy first-degree relatives of individuals with schizophrenia and related disorders and 54 non-psychiatric controls. Potential associations between SPQ subscales and UPSIT score were examined while considering the effects of sociodemographic variables on these measures.

RESULTS

SPQ and UPSIT scores were not significantly different in first-degree relatives and controls. There was no evidence of an association between SPQ domains and UPSIT score, even when controlling for possible confounding variables, including age and educational attainment.

CONCLUSIONS

The nascent literature on potential associations between schizotypy and olfactory identification ability has yielded mixed findings to date. The current study does not support a correlation between these two markers, and this lack of association--in addition to equal olfactory identification performance in relatives and controls--casts doubt on the utility of the UPSIT as a measure of an endophenotypic trait. Future research would benefit from larger, more diverse samples; the addition of objective, interviewer-based measures of schizotypy; and attention to potentially confounding sociodemographic variables.

Avaliação neuropsicológica dos circuitos pré-frontais relacionados à tomada de decisão na esquizofrenia: uma revisão sistemática da literatura

OBJETIVOS: Realizou-se uma revisão crítica da literatura sobre estudos avaliando déficits neuropsicológicos na tomada de decisão (TD) em pacientes esquizofrênicos. MÉTODO: Foram considerados relevantes estudos utilizando testes neuropsicológicos sensíveis à avaliação das áreas corticais associadas à TD, principalmente o córtex órbito-frontal. Aspectos metodológicos dos estudos selecionados foram comparados entre si, assim como a correlação das medidas nos testes de TD com características clínicas, cognitivas e funcionais desse transtorno. RESULTADOS: Foram selecionados oito artigos entre 1997 e 2005. Seis utilizaram como instrumento para avaliação da TD o Iowa Gambling Task; um, o Novel Decision Making Task; e outro, o Two-Choice Prediction Task. Todos os estudos compararam pacientes esquizofrênicos a controles saudáveis. Quatro artigos com o Iowa Gambling Task e os demais utilizando os testes Novel Decision Making Task e o Two Choice Prediction Task observaram desempenho alterado no grupo de pacientes esquizofrênicos. DISCUSSÃO E CONCLUSÃO: Os estudos atuais são controversos quanto ao comprometimento da TD na esquizofrenia. Características clínicas, como o subtipo diagnóstico, a sintomatologia predominante, o tipo de medicação utilizada e o funcionamento psicossocial, podem contar para os resultados encontrados. Estudos adicionais são necessários para a investigação ulterior sobre a natureza dos déficits da TD na esquizofrenia e sua expressão em termos clínicos e evolutivos.

Associations between olfactory identification and verbal memory in patients with schizophrenia, first-degree relatives, and non-psychiatric controls

OBJECTIVE

Olfactory identification deficits and verbal memory impairments may represent trait markers for schizophrenia. The aims of this study were to: (1) assess olfactory identification in patients, first-degree relatives, and non-psychiatric controls, (2) determine differences in verbal memory functioning in these three groups, and (3) study correlations between olfactory identification and three specific verbal memory domains.

METHOD

A total of 106 participants-41 patients with schizophrenia or related disorders, 27 relatives, and 38 controls-were assessed with the University of Pennsylvania Smell Identification Test (UPSIT) and the Wechsler Memory Scale-Third Edition. Linear mixed models, accounting for clustering within families and relevant covariates, were used to compare scores across groups and to examine associations between olfactory identification ability and the three verbal memory domains.

RESULTS

A group effect was apparent for all four measures, and relatives scored midway between patients and controls on all three memory domains. UPSIT scores were significantly correlated with all three forms of verbal memory. Age, verbal working memory, and auditory recognition delayed memory were independently predictive of UPSIT scores.

CONCLUSIONS

Impairments in olfactory identification and verbal memory appear to represent two correlated risk markers for schizophrenia, and frontal-temporal deficits likely account for both impairments.

Olfactory deficits, cognition and negative symptoms in early onset psychosis

BACKGROUND

Smell identification deficits (SID) are common in adult schizophrenia, where they are associated with negative symptoms and lower intelligence. However, smell identification has not been examined in adolescents with early onset psychosis, wherein diagnosis is often obscure, and there are few prognostic predictors.

METHOD

We examined smell identification, diagnosis, neuropsychological performance and symptoms in 26 well characterized adolescents with early onset psychosis, age 11-17 years.

RESULTS

SID existed in the sample and were more common in patients with schizophrenia and psychotic depression than in patients with psychosis NOS and bipolar disorder. As in adults, SID were significantly associated with greater negative symptoms and lower verbal IQ. However, the associations of verbal IQ (and other verbal tasks) to smell identification in this pediatric sample were explained by the relation of both of these types of variables to negative symptoms.

CONCLUSIONS

SID existed across this sample of youths with psychotic disorder, and were specifically related to typical characteristics of schizophrenia, such as negative symptoms and lower intelligence, but not to features of bipolar disorder, such as grandiosity. SID is a characteristic of early onset psychosis that may be useful for prognostic purposes.

Characterization of olfactory bulb glomeruli in schizophrenia

Olfactory deficits, observed in schizophrenia, may be associated with a disruption of synaptic transmission in the olfactory system. Using immunohistochemistry and optical densitometry, we assessed the integrity of the synaptic connection between olfactory receptor neurons and olfactory bulb target neurons in schizophrenia by comparing the level of eight proteins, expressed in the olfactory bulb glomeruli, among schizophrenia and control subjects. In schizophrenia, no change was observed in the levels of OMP, GAP43 and NCAM, proteins expressed by olfactory receptor neurons, suggesting an intact innervation of the olfactory bulb by these neurons. This was supported by the absence of change in calbindin level, which has been shown to decrease after the destruction of the olfactory epithelium. The level of synaptophysin, a pre-synaptic protein, was also unchanged. These findings suggested that axons of olfactory receptor neurons establish synapses with their olfactory bulb targets in schizophrenia. The absence of change in the level of poorly phosphorylated neurofilament of moderate and high molecular weight (NFM/HP) suggested no lack of dendritic innervation despite a previously seen reduction of glomerular MAP2 level in schizophrenia subjects. This and above findings were consistent with the absence of change in the level of beta-tubulin III, a protein expressed by neurons of both olfactory epithelium and bulb. Finally, we noted no significant decrease in trkB level, a neurotrophin receptor involved in the olfactory epithelium maintenance. This study showed no evidence of major structural alteration of the synapse between the olfactory epithelium and bulb in schizophrenia.

Olfactory functions and volumetric measures of orbitofrontal and limbic regions in schizophrenia

OBJECTIVE

Olfactory deficits in schizophrenia patients have been suggested to reflect medial temporal and/or prefrontal brain abnormalities. In this study, we examined the relationship between different olfactory functions and volumes of the hippocampus-amygdala complex (HAC) and the orbitofrontal brain region using magnetic resonance imaging (MRI).

METHODS

Thirty-three young men with schizophrenia (DSM-IV) and 40 healthy controls performed unirhinal olfactory assessment including the main olfactory functions (threshold, discrimination, and identification), and odor judgements (intensity, edibility, familiarity, and pleasantness). Volumes of regions in the medial temporal lobe (hippocampus and amygdala) and the prefrontal region (orbitofrontal gray and white matter) were measured on MRI scans.

RESULTS

Compared with controls, patients showed bilaterally impaired thresholds, quality discrimination and identification, as well as edibility judgements. Olfactory deficits were not attributable to smoking, premorbid intelligence, or impaired thresholds. Relative to controls, patients had bilateral reduced hippocampus and amygdala volumes. In patients, smaller hippocampus volumes were associated with poorer olfactory discrimination ability.

CONCLUSIONS

Olfactory deficits in schizophrenia appear to be associated with morphometric abnormalities in the medial temporal rather than the orbitofrontal region (OFR). These results indicate that olfactory quality discrimination deficits are related to structural hippocampus abnormalities. Future studies of genetic and behavioral high-risk samples seem warranted.

Trail making and olfaction in schizophrenia: implications for processing speed

BACKGROUND

Previous research has established a relationship between smell identification deficits (SID) and particular aspects of cognitive function among patients with schizophrenia.

OBJECTIVE

To expand the extant literature, we examined the relationship between SID and the Trail Making Test to determine if processing speed is related to SID.

METHODS

Our sample included 60 inpatients from the New York State Psychiatric Institute's Schizophrenia Research Unit. We considered age, deficit syndrome, verbal intelligence quotient, and education in our analyses due to their documented relationship to smell identification ability.

RESULTS

Trails A errors and Trails A seconds accounted for a significant amount of the variance in University of Pennsylvania Smell Identification Test scores in a regression analysis (R2=.10, P=.008 and R2=.05, P=.04).

CONCLUSION

Linking neurocognition to smell identification deficits may prove to be an essential marker for schizophrenia research.

The Smell Identification Test as a Measure of Olfactory Identification Ability in Schizophrenia and Healthy Populations: A Rasch Psychometric Study

This study examines University of Pennsylvania Smell Identification Test (UPSIT; R. L. Doty, 1995) performance in 133 controls and 54 chronic, medicated outpatients with schizophrenia (SZ) using item-response theory modeling. Results show that UPSIT items contribute to 1 factor, cover a range of 8 standard errors of measurement, and articulate 3 ability levels. Although it is not difficult enough to discriminate among persons of above-average ability, the test has diagnostic utility in detecting moderate impairment. Independent of item difficulty, 13 items differentiate patients from controls. When 45 patients and 45 controls were matched on gender and age, patient accuracy remained significantly reduced. The findings support the test's utility and demonstrate how traditional data analysis is insensitive to complexities in test performance.

A brief smell identification test discriminates between deficit and non-deficit schizophrenia

Evidence is accumulating that smell identification deficits (SID) and social dysfunction in schizophrenia may share a common pathophysiology. While most schizophrenia studies utilize the lengthy 40-item University of Pennsylvania Smell Identification Test (UPSIT) to assess smell identification ability, a brief 12-item smell identification test (B-SIT) has recently been constructed as a culturally neutral substitute for the UPSIT. By selecting the 12 items of the UPSIT from which the B-SIT was originally derived, we constructed a proxy for the B-SIT and compared the performance of 83 patients with schizophrenia to 69 normal subjects. We examined select properties of the B-SIT proxy in relation to the UPSIT to determine its efficacy for use in psychiatric populations. We considered the sensitivity of the B-SIT proxy and evaluated a cutoff score for identifying deficit syndrome schizophrenia (DS). The UPSIT and B-SIT proxy were significantly related in the patients (n=83, r=0.85, P=0.01) and in comparison subjects (n=69, r=0.83, P=0.01), and both measures similarly distinguished DS from non-deficit syndrome (non-DS) patients. The results of this study support the utility of the B-SIT for schizophrenia research and highlight the robustness of the relationship between SID and social dysfunction in schizophrenia.

Scent of a disorder: olfactory functioning in schizophrenia

The use of olfactory probes to assess frontal and temporal-limbic system functioning in patients with schizophrenia has garnered increasing interest among basic and clinical investigators. Deficits in odor identification, detection threshold sensitivity, discrimination, and memory have been reported and are thought to represent a centrally mediated deficit in the processing of this information. These impairments are seen in affected probands, first-degree family members, and those at risk for developing the illness, suggesting a genetic vulnerability or predisposition to chemosensory abnormalities. The observed deficits are not explained by gender, medication use, cognitive impairment, or smoking status, and support the hypothesis of primary dysfunction in the olfactory system. Along this same line, structural abnormalities in the peripheral and central olfactory brain regions, as well as disruptions of the basic physiology of this system, have been described. The study of olfactory processing in schizophrenia has already advanced the knowledge of the neural substrate for this disorder. Because the olfactory system continuously regenerates throughout life, it allows for a unique view of an ongoing neurodevelopmental process.

Auditory temporal processing in schizophrenia: high level rather than low level deficits?

INTRODUCTION

Patients with schizophrenia demonstrate a wide range of information processing deficits. Most recent studies argue in favour of high level deficits, including attention and context processing, whereas fewer studies have demonstrated deficits at earlier stages of processing, such as perceptual discrimination and organisation. This is the first study to investigate both high and low level processing, within a single paradigm, in the case of auditory temporal processing in schizophrenia.

METHODS

Patients with schizophrenia were compared to controls on a series of tasks involving three auditory temporal processes varying from low to higher level: (1) segregation of a complex sequence into component auditory streams; (2) detection of local temporal irregularities within a stream; (3) attentional focusing on one stream by the use of a cue preceding the complex sequence.

RESULTS

The lowest level of processing examined here--stream segregation--appeared to function equally well in patients as in controls. However, the higher level processes--irregularity detection and attentional focus--functioned in both groups, but less efficiently in patients with schizophrenia.

CONCLUSIONS

Results demonstrate abnormal auditory temporal processing in schizophrenia. Abnormal performances only in Processes 2 and 3 support and hypothesis of higher level rather than lower level processing deficits in schizophrenia.

Visual backward-masking deficits in schizophrenia: relationship to visual pathway function and symptomatology

Patients with schizophrenia have information processing deficits which can be measured using visual backward-masking (VBM) tasks. There are two types of visual pathways: transient and sustained. The former is more sensitive to low spatial frequency (LSF) and the latter to high spatial frequency (HSF) stimuli. It has been hypothesized that the VBM deficit in schizophrenia is due to an overactive transient channel response to the mask. To examine this hypothesis, patients with schizophrenia and comparison volunteers were tested on a traditional backward-masking task as well as on tasks that altered the mask to bias stimulation toward transient (LSF) or sustained (HSF) channels. Medication effects and relationship to symptomatology were also examined. Patients with schizophrenia showed a significant deficit on the traditional backward-masking task and were also significantly impaired on the LSF- and HSF-masking tasks, though a differential deficit was not found on the latter two tasks. A U-shaped function, indicative of masking by interruption, was found on the LSF- and HSF-masking tasks. Masking performance was not altered when the same patients were tested on and off medication, and performance was related to positive and negative symptoms. In conclusion, the finding of a deficit in patients with schizophrenia on tasks producing a U-shaped function suggests that an aberrant transient response to the mask is producing increased interruption of the sustained response to the target.

Odor identification, eye tracking and deficit syndrome schizophrenia

BACKGROUND

Deficit syndrome (DS) schizophrenia patients have smooth pursuit eye movement (SPEM) dysfunction. We examined if they also had smell identification deficits, since social affiliation is related to olfaction in other mammals.

METHODS

Sixty-seven patients had DS assessments: 31 patients had SPEM and 50 had Smell Identification Test (SIT) assessments, and 14 patients had both measurements.

RESULTS

DS patients had worse SPEM and SIT performance than the non-DS patients. Areas under the receiver-operator characteristic (ROC) curves for SIT and SPEM were both fairly accurate in identifying the DS. The odds ratio (OR) for the DS for impaired versus normal SPEM was 6.21 (95% confidence interval [CI]: 1.21, 32.25) and for microsmia versus normosmia was 10.4 (95% CI: 1.23, 88.18). Further analyses showed that the association of SIT with both SPEM and the DS could account for the SPEM-DS association.

CONCLUSIONS

We found a strong association between the DS and SIT scores suggesting that the neural substrates of olfaction may be related to social affiliation in humans, as they are in other mammals. These data further support the notion that the DS defines a homogeneous subgroup of schizophrenia patients and further suggest that dysfunction in the neural circuitry of olfaction may contribute to its pathophysiology.

Odor identification impairments in schizophrenia: relationship with demographic measures, clinical variables, and diagnostic subtypes

Smell identification deficits are consistently found in schizophrenia (SZ), but little is known about the nature and characterization of this deficit or its relationship to the phenomenology of the illness. This study aims to further delineate smell identification errors in SZ by examining the relationship of patient demographic differences with smell-identification performance. Our results showed that a patient's gender and education were related to odor-identification scores, with better performance seen in female patients and in those with greater educational attainment. However, there was no effect related to age, ethnicity, or socioeconomic status on odor identification. A smell identification deficit was also unrelated to clinical characteristics of the patients, including age at first hospitalization, number of psychiatric hospitalizations, and duration of illness. Odor identification also did not differ by SZ subtype, nor between SZ and schizoaffective disorder patients. These findings emphasize that odor identification deficits in SZ are unrelated to clinical illness features, cannot be explained by other confounds related to olfaction in the general population, and may be core features related to the SZ disease process.

Unilateral olfactory perception and magical ideation

We assessed olfactory detection thresholds and discrimination abilities in 40 healthy right-handers (20 women and 20 men). All subjects were also required to complete the Magical Ideation (MI) scale, a well-validated 30-item schizotypy inventory. Over both nostrils, we found elevated thresholds for subjects with high MI scores (at or above the median score of 9.0) compared with those with low scores. In men but not women, specifically left-nostril acuity was inversely correlated to MI raw scores. MI was unrelated to olfactory discrimination performance. These results suggest an association, at least in healthy men, between even moderate signs of schizotypy and deficits in odor detection. The selective impairment of left-nostril performance adds to the growing evidence for left temporal lobe functional abnormalities in people high on MI. This laterality effect is known from previous studies in patients with schizophrenia. However, as a rule, in psychiatric patients olfactory identification rather than simple detection performance was found to be impaired, indicating that the integration of odor information is affected at different levels of processing in schizotypy compared with schizophrenia. Work with completely normal subjects may reasonably complement clinical studies of olfactory perception. Among its advantages are the good subject compliance and the absence of medication effects.

Asymmetrical olfactory acuity and neuroleptic treatment in schizophrenia

Uni-rhinal olfactory acuity in schizophrenia was investigated in two experiments. The first assessed the presence of a predicted atypical asymmetry of nostril laterality and the second assessed the effect of antipsychotic treatment on the asymmetry. Although olfactory identification impairment has been well documented in schizophrenia, olfactory acuity has been neglected. This may be an oversight as cerebral structures of the mesial temporal lobe important to olfactory perception have often been implicated in the pathophysiology of schizophrenia and it is thus reasonable to postulate a primary impairment of olfactory acuity in schizophrenia. In addition, unmedicated patients with schizophrenia have exhibited asymmetrical laterality favouring the right over the left hemisphere in studies of visual, haptic, and auditory perception, and the few published prospective treatment studies have suggested a reversal of this asymmetry with first generation neuroleptic treatments. In experiment 1 a generalization of the perceptual asymmetry to olfactory acuity was examined by measurement of n-butanol olfactory thresholds with the Connecticut Chemosensory Perception Exam (CCPE) in an unmedicated sample of 17 patients with schizophrenia and 17 age, gender, and handedness matched normal controls. The patient sample showed an asymmetrical impairment of the left nostril that was not apparent in the normal control sample. In experiment 2, the CCPE was administered to a new sample of 10 patients with schizophrenia before and after neuroleptic treatment. The asymmetry observed in experiment 1 was replicated, and the relative advantage of the right nostril shifted to a relative advantage of the left nostril over the course of 8weeks of treatment. Results are discussed in relation to cerebral aspects of schizophrenia and potential implications to cognitive change from treatment.

Olfactory identification in combat-related posttraumatic stress disorder

Recent neuropsychological conceptualizations of posttraumatic stress disorder (PTSD) implicate dysfunction of the fronto-limbic system, a brain system thought to be involved in the mediation of emotion. However, few studies have examined fronto-limbic subregions, such as the orbitofrontal cortex, in PTSD. As a measure of orbitofrontal integrity, olfactory identification was assessed in 26 Vietnam War veterans with PTSD, 25 Vietnam War veterans without mental disorders, and 17 Vietnam-era, non-war-zone veterans without mental disorders. Relative to veterans without PTSD, those diagnosed with PTSD were less proficient in odor identification and verbal learning but not on other cognitive tests sensitive to dorsolateral prefrontal and mesial temporal functioning. Results bolster prior research indicating fronto-limbic dysfunction in PTSD, and suggest involvement of the orbitofrontal region.

Smooth pursuit eye movements to extra-retinal motion signals: deficits in patients with schizophrenia

In order to understand mechanisms underlying the smooth pursuit abnormality(ies) in schizophrenia, new methods, which independently evaluated predictive smooth pursuit responses to extra-retinal motion signals, were developed and tested. The study compared responses to only extra-retinal motion signals in normal volunteers (n = 25), and individuals with a chronic (n = 21) and a recent onset (n = 18) schizophrenia. Subject groups with chronic schizophrenia and recent onset schizophrenia had significantly poorer predictive pursuit than normal subjects in response to only extra-retinal motion signals. The poor predictive pursuit was evident even at low target velocity when the closed-loop pursuit gain was normal in patients with schizophrenia. Ten of the 18 recent onset patients were drug-free at the time of testing and had no or minimum previous exposure to anti-psychotic medications. Re-analyses of the data showed that on most measures of predictive pursuit, drug-free patients were not significantly different from patients who received anti-psychotic drug treatment. Both patient groups had significantly poorer predictive pursuit than normal subjects. These results suggest that a deficit in processing extra-retinal motion may underlie the abnormal smooth pursuit response in schizophrenia. At low target velocities, patients with schizophrenia were able to compensate for the low extra-retinal gain by increasing the gain of response to the retinal slip velocity. This indicates that patients were able to process retinal slip velocity and generate smooth pursuit eye movements, but experienced a specific deficit in processing and/or integrating extra-retinal motion information for the smooth pursuit response.

Olfactory identification and psychosis

BACKGROUND

Olfactory identification performance has been investigated in several psychiatric populations, with deficits most commonly reported in patients with schizophrenia. In this study, olfactory identification performance was investigated in a more homogenous group of treatment-refractory patients with schizophrenia (T-RS) and in two additional psychiatric groups who demonstrate some similarities to the patients with schizophrenia in terms of symptomotology and medication regime.

METHODS

The olfactory identification performance of 16 T-RS patients was assessed using the University of Pennsylvania Smell Identification Test (UPSIT) and compared to that of 16 normal control subjects and two other psychiatric patient groups: 19 affective disorder patients requiring maintenance antipsychotic medication and 20 affective disorder patients not receiving antipsychotic medication.

RESULTS

The olfactory identification performance of T-RS patients was significantly lower than that of normal controls but not significantly different from either affective disorder group. The olfactory identification performance of affective disorder patients receiving antipsychotic medication was significantly lower than that of affective disorder patients not receiving antipsychotic medication.

DISCUSSION

Results are discussed in the context of a possible link between psychotic symptomotology and olfactory identification performance.

Cellular and molecular neuropathology of the olfactory epithelium and central olfactory pathways in Alzheimer's disease and schizophrenia

Specific deficits in odor detection threshold, identification, and memory have been recognized in a variety of disorders including the neurodegenerative disorder, Alzheimer's disease (AD), and the psychiatric illness, schizophrenia, which is likely due to abnormalities in neurodevelopment. Neuropathological abnormalities in peripheral and central olfactory systems have been described in both disorder. In the olfactory, epithelium, dystrophic neurites that are immunoreactive for tau, neurofilaments and other polypeptides, as well as deposits of beta-amyloid have been observed, and these findings have been thought to contribute to the olfactory dysfunction of these disorders. However, similar findings also occur in the olfactory epithelium of many normal individuals and those with various other neurodegenerative diseases. In contrast, neuropathological studies have reported selective vulnerability of central olfactory pathways for the accumulation of neurofibrillary pathology in AD, and for cytoarchitectural, neuronal morphometric, and cytoskeletal protein abnormalities suggestive of abnormal neurodevelopment in schizophrenia. Thus, it is likely that the olfactory impairments associated with these diseases are due to damage within central olfactory pathways, and that they are further amplified by the less specific impairments associated with age-related sensory neuroepithelial abnormalities. Finally, both the olfactory epithelium and central olfactory pathways represent model systems in which to study the neurobiology of these disorders, which ultimately may yield clues with diagnostic and therapeutic utility.

Neuropsychological, neurological and symptom correlates of impaired olfactory identification in schizophrenia

Impaired olfactory identification has been reported in samples of schizophrenic patients. Little is known about the associations between these impairments and neuropsychological deficits, neurological deficits and olfaction-related symptoms. Forty-six subjects (37 men and 9 women) with schizophrenia were examined with the University of Pennsylvania Smell Identification Test (UPSIT), a selection of neuropsychological tests and standardised neurological and symptom evaluations. Eighty-five per cent of the subjects scored below the published norms' 10th percentile on the UPSIT. Stepwise multiple regression found that WAIS-R Information score and Wisconsin Card Sort Test Failure to Maintain Set score (WCST-FMS) were the only significant predictors of the UPSIT percentile scores, accounting for 41% of the variance. Neurological signs did not contribute to the prediction of impaired olfactory identification. Although 26% of subjects reported olfactory hallucinations, there was no association between this symptom and olfactory impairment. The results suggest that general knowledge or general intelligence may have some influence on olfactory identification in subjects with schizophrenia; however, olfactory identification deficit could not be explained by gross impairments of sustained attention, memory or conceptual ability.

SPECT imaging of odor identification in schizophrenia

Deficits in olfactory identification, despite normal odor perception, are found in some neuropsychiatric disorders, including schizophrenia. We examined if regional cerebral blood flow (rCBF) differed between schizophrenia patients and controls during odor identification, hypothesizing that these brain regions could be relevant to odor identification impairments. Eight schizophrenia and eight comparison subjects provided a baseline (picture identity matching) and activation (odor identification) SPECT scan, obtained using 99mTc-HMPAO in a low dose/high dose design. Six patients and seven controls had analyzable data. MEDX data saved in ANALYZE format for SPM 95 generated paired t-test statistical data for display in Talairach space, with rCBF changes given as Z-scores. There was no schizophrenia vs. control group difference in rCBF for the baseline picture-matching test. For odor identification, schizophrenia patients had a hypometabolic right-sided cortical region that included the frontal lobe Broca's area, superior temporal lobe, and supramarginal and angular gyri. Post hoc within-group contrasts of picture-matching vs. odor identification showed that the controls significantly increased rCBF in the right-sided inferior temporal fusiform gyrus, and bilateral hippocampi and visual association areas for the odor test. The schizophrenia group showed no rCBF differences for picture-matching compared to odor identification. Patients showed significant hypometabolism in right-sided cortical areas for odor identification. They also failed to show increased rCBF in the hippocampus and visual association area, as seen in controls for odor identification compared to picture-matching. These regions may be unique to schizophrenia or have broader implications for olfactory memory retrieval.

Operant conditioning and the orbitofrontal cortex in schizophrenic patients: unexpected evidence for intact functioning

Neuroimaging and neuropsychological studies have consistently implicated dorsolateral prefrontal cortex as abnormal in schizophrenia. However, other areas of frontal cortex have received far less attention. In particular, few studies have examined orbital frontal regions with other than olfactory tests. In the present study we wished to assess the functional capability of orbital frontal cortex using a test developed by Bechara et al. (1994) that assesses a subject's capacity to acquire a preference through reward and punishment, using a gambling task that involved gains and losses of play money. Thirty normal subjects and 12 patients with schizophrenia (three undifferentiated, eight paranoid, one schizoaffective) comprised the sample in the present study. We found that patients with schizophrenia exhibited a pattern of findings similar to that of normals and dissimilar to that of patients with known orbital frontal damage. In our study, both normal subjects and schizophrenic patients chose most frequently from decks of cards in which there were frequent rewards and infrequent penalties, as might be expected on the basis of operant conditioning literature. We also found that performance on this task was not correlated with tests of working memory or long-term memory, suggesting that the development of a preference may occur implicitly. Our findings also argue against a general deficit in schizophrenia, as performance on the gambling task appeared relatively uncompromised.

Olfactory identification deficit in relation to schizotypy

Past studies have shown that schizophrenic men tend to be impaired on the olfactory identification task. We examined individual differences in the olfactory function in relation to schizotypy. Healthy individuals who might carry latent liability for schizophrenia participated in olfactory identification and acuity tasks. Psychometrically ascertained schizotypic men showed deficits on the olfactory identification task but not on the olfactory acuity task. The olfactory identification function partly depended on the menstrual cycle in women. But further systematic research is needed to clarify the possible role of estrogen.

Sex differences in olfactory identification and Wisconsin Card Sorting performance in schizophrenia: relationship to attention and verbal ability

We investigated the hypothesis that different prefrontal brain systems (i.e., dorsal vs. ventral) and sex contribute differentially to cognitive deficit in schizophrenia. Performance was assessed among clinically stable, chronic schizophrenic outpatients and matched normal control subjects on olfactory identification [on the University of Pennsylvania Smell Identification Test (UPSIT)] and on executive functions [using the Wisconsin Card Sorting Test (WCST)]. Patients were impaired on both tests compared to controls, and male schizophrenics were impaired on the WCST compared to female schizophrenics. The pattern of results suggests that gender differences on the UPSIT are mildly accentuated in schizophrenia. The data support our previous study indicating that UPSIT performance is largely independent of the executive or attentional deficits typically associated with schizophrenia, with the exception of verbal ability. Further research with larger samples is required to test the hypothesis that there is a severely impaired subgroup of male patients with diffuse prefrontal dysfunctions.

The N-methyl-D-aspartate antagonists phencyclidine, ketamine and dizocilpine as both behavioral and anatomical models of the dementias

Phencyclidine (PCP) and ketamine can induce a model psychosis in drug addicts and exacerbate the symptoms of chronic schizophrenics. The model psychoses these drugs induce mimic a variety of schizophrenic symptoms, including flattened affect, dissociative thought disorder, depersonalization and catatonic states. These symptoms can persist for prolonged periods and chronic PCP and ketamine addicts have persisting memory deficits. Dizocilpine (MK-801) is a simpler drug than PCP or ketamine in its actions, but it shares with both the property of blocking in a non-competitive manner the N-methyl-D-aspartate (NMDA) ion-channel. Behavioral observations and drug-discrimination studies in animals indicate that PCP and dizocilpine are similar in their effects and they both have a neurotoxic effect on neurons in posterior cingulate cortex. Recent studies have indicated that both of these drugs, when given continuously for several days, further induce neuronal degeneration in other limbic structures. These include brain regions of rats related to olfaction, associated limbic structures such as piriform cortex and posterior regions of entorhinal cortex and in it's projections, through the perforant pathway, to dentate gyrus and other cells in ventral hippocampus. These degenerative consequences may be excitatory neurotoxic effects, for these compounds also induce an elevation in glucose metabolism maximal in just those structures where degeneration is observed and the degeneration involves entire cells, with all of their processes. It has been suggested these non-competitive NMDA antagonists induce an increase in firing rate in a limbic circuit which includes the perforant pathway. At least some competitive NMDA antagonists induce the same pattern of degeneration and altered glucose utilization. There is anatomical and functional evidence that alterations in these same limbic structures are present in the dementia syndrome manifested by some schizophrenics and most Alzheimer's patients. This suggests that these non-competitive NMDA antagonists may provide a more complete model of psychoses and memory disturbances than previously recognized, in that they can mimic both persisting symptomatology and neuroanatomical abnormalities. While the neurochemical underpinnings of this effect remain elusive, it appears to be both age and sex dependent. Further studies of the mechanisms by which NMDA antagonists induce increased glucose utilization and neurotoxicity in these limbic structures may clarify these alterations in this simplified Papez-like circuit.