Olfactory identification and discrimination in obsessive-compulsive disorder

Associations between olfactory dysfunction and cognition: a scoping review

INTRODUCTION

Strong evidence suggests that olfactory dysfunction (OD) can predict additional neurocognitive decline in neurodegenerative conditions such as Alzheimer's and Parkinson's diseases. However, research exploring olfaction and cognition in younger populations is limited. The aim of this review is to evaluate cognitive changes among non-elderly adults with non-COVID-19-related OD.

METHODS

We performed a structured comprehensive literature search of PubMed, Ovid Embase, Web of Science, and Cochrane Library in developing this scoping review. The primary outcome of interest was the association between OD and cognitive functioning in adults less than 60 years of age.

RESULTS

We identified 2878 studies for title and abstract review, with 167 undergoing full text review, and 54 selected for data extraction. Of these, 34 studies reported on populations of individuals restricted to the ages of 18-60, whereas the remaining 20 studies included a more heterogeneous population with the majority of individuals in this target age range in addition to some above the age of 60. The etiologies for smell loss among the included studies were neuropsychiatric disorders (37%), idiopathic cause (25%), type 2 diabetes (7%), trauma (5%), infection (4%), intellectual disability (4%), and other (18%). Some studies reported numerous associations and at times mixed, resulting in a total number of associations greater than the included number of 54 studies. Overall, 21/54 studies demonstrated a positive association between olfaction and cognition, 7/54 demonstrated no association, 25/54 reported mixed results, and only 1/54 demonstrated a negative association.

CONCLUSION

Most studies demonstrate a positive correlation between OD and cognition, but the data are mixed with associations less robust in this young adult population compared to elderly adults. Despite the heterogeneity in study populations and outcomes, this scoping review serves as a starting point for further investigation on this topic. Notably, as many studies in this review involved disorders that may have confounding effects on both olfaction and cognition, future research should control for these confounders and incorporate non-elderly individuals with non-psychiatric causes of smell loss.

Evaluation of Nasal Mucociliary Clearance as an Indicator of Nasal Function in Obsessive-Compulsive Patients: A Cross-Sectional Study

This clinical study aimed to compare the mucociliary clearance time in patients with OCD, a disease associated with neural olfactory disorders, with a healthy control group. The mucociliary clearance time of fifty-one patients with OCD and fifty-two healthy patients (control group) was compared. The saccharin nasal mucociliary clearance test (NMCT) was applied and recorded the sociodemographic data of all participants. The NMCT was longer in OCD patients than healthy controls. There was no statistically significant difference in sociodemographic data between the groups. Our results show that olfactory transmission pathways may be affected in OCD patients.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12070-023-03972-2.

Olfaction and Executive Cognitive Performance: A Systematic Review

Objective tests of olfaction are widely available to aid in the assessment of olfaction. Their clearest role is in the characterization of olfactory changes, either reported by or suspected in a patient. There is a rapidly growing literature concerned with the association of olfactory changes with certain neuropsychiatric conditions and the use of olfactory testing to supplement conventional assessments in clinical and research practice is evolving. Neural pathways important for olfactory processing overlap extensively with pathways important for cognitive functioning, and especially those important for executive functioning, many of which are concentrated in the frontal lobes. Previous work has identified associations between performance on certain olfactory tests (most frequently olfactory identification) and executive functioning and behavioral measures (e.g. of impulsivity). More recently, similar associations have also been identified in non-clinical samples, raising new questions as to the utility of olfactory test scores as proxy measures for non-olfactory phenomena. In this systemic review, we sought to identify studies, both clinical and non-clinical, that investigated the associations of olfaction with performance on tasks sensitive to frontal lobe functioning. Our search criteria led to the identification of 70 studies published in English. We examined in detail and tabulated the data from these studies, highlighted each study's key findings, and critically evaluated these studies. We use the results of this review to reflect on some of the current and future challenges concerning the use of olfactory testing in clinical neuropsychiatric practice and research and speculate on the potential benefits of administering phonemic fluency in combination with olfactory testing to enhance its predictive value.

Olfactory capacity in anorexia nervosa: correlations with set-shifting ability

PURPOSE

The purpose of this study is to examine olfactory capacity in adults with anorexia nervosa (AN), in terms of odor identification and odor threshold and search for possible correlations between odor identification and cognitive flexibility in this population.

METHODS

Thirty-nine patients diagnosed with AN and 60 healthy participants, participated. Odor identification was assessed using the University Pennsylvania Smell Identification Test and a two alternative forced choice, ascending method with n-butanol was used to assess odor threshold. Cognitive flexibility was determined using the Intra/Extra-Dimensional Set-Shift test (IED), a subtest of the Cambridge Neuropsychological Test Automated Battery (CANTAB).

RESULTS

Patients with AN presented a poorer performance in odor identification compared with controls (p = 0.001). No differences were found in odor threshold, between the two groups. Patients with AN exhibited poor cognitive flexibility compared with controls (p = 0.003). A significant correlation between odor identification and cognitive flexibility was documented in AN (p = 0.01), but not in controls.

CONCLUSION

Our findings suggest that olfactory capacity is altered in AN: Qualitative characteristics of olfaction were affected in patients with AN (lower odor identification), while there was no difference in quantitative characteristics (odor threshold) compared with controls. Furthermore, odor identification in AN was correlated to cognitive flexibility.

LEVEL OF EVIDENCE

Level III: case-control analytic study.

Olfactory identification impairment in early-and late-onset obsessive-compulsive disorder

BACKGROUND

Early-onset obsessive-compulsive disorder (EOCD) is a comparatively severe subtype of obsessive-compulsive disorder (OCD). Olfactory dysfunction is a common symptom of OCD, but all previous studies have focused on late-onset OCD (LOCD).

METHODS

The current study compared olfactory identification ability in EOCD patients and age-matched and sex-matched LOCD patients and healthy controls. Thirty patients with EOCD, 30 patients with LOCD and 30 healthy controls were included in the study. Olfactory function was measured using the University of Pennsylvania Smell Identification Test. The Logical Memory and Visual Reproduction components of the Revised Wechsler Memory Scale were used to evaluate verbal and visual memory.

RESULTS

There were significant differences in olfactory identification ability between the three groups. EOCD patients were comparable to LOCD patients, while both patients' group showing worse olfactory identification ability than controls. Olfactory identification ability was not significantly correlated with verbal and visual memory or clinical symptoms in the EOCD group or the LOCD group.

CONCLUSIONS

The results of the present study suggest that olfactory identification ability may be a relatively stable indicator of OCD, independent of age, duration of illness, verbal and visual memory, and severity of clinical symptoms.

The Savage Organizational Scoring System for the Rey-Osterrieth Complex Figure Test: Norms and New Data From Veterans in a Traumatic Brain Injury Clinic

The Rey-Osterrieth Complex Figure Test (RCFT) permits quantifying diverse cognitive abilities, including executive function (EF). We evaluated the psychometric properties of a scoring procedure for the RCFT, the Savage Organizational Scoring System (SOSS), that awards points for drawing the largest structural elements of the figures as continuous wholes. This was a two-phase study: first, we conducted a systematic literature search for studies using the SOSS, and aggregated previously published data for healthy controls to create a normative database; second, we observed performances from veterans evaluated for traumatic brain injury (TBI), examining the reliability of their SOSS scores, the SOSS correlations with two EF measures and the participants' self-reported cognitive functioning, and then compared their mean scores to normative expectations. Across our literature-derived normative database, the aggregated mean SOSS score was 4.12 (SD = 1.72), which was marginally higher than that of our veteran participants evaluated for TBI, 3.72 (SD = 1.79). The SOSS had modest internal consistency (α = .59). Unlike the criterion EF measures, the SOSS was not significantly related to self-reported cognitive functioning. The SOSS shared a small, significant correlation with Trails B and Shipley Abstraction; but RCFT Copy scores were more strongly related to these tests, and the SOSS added no significant incremental predictive value beyond the RCFT Copy score. However, SOSS scores did predict RCFT Recall beyond RCFT Copy scores. We conclude that the SOSS has modest reliability and is predictive of RCFT Recall scores, but it is not strongly correlated with other EF measures, and it is only minimally affected by mild TBI.

Association Between Anxious Symptom Severity and Olfactory Impairment in Young Adults with Generalized Anxiety Disorder: A Case-Control Study

OBJECTIVE

The findings of olfaction are inconsistent in anxiety disorders, and few studies have reported on the olfactory performance in generalized anxiety disorder (GAD). Therefore, we aim to investigate the olfactory function of patients with GAD and the association between olfactory function and anxiety symptoms.

METHODS

We conducted a case-control study by selecting 107 patients with GAD and 107 healthy controls matched for sex and age, to investigate olfaction deficits in GAD and the association between anxiety severity and olfaction. All patients were treatment-naïve prior to the inclusion. Anxiety severity and olfaction were assessed by the Hamilton anxiety rating scale (HAM-A) and the Sniffin' Sticks test (SST), respectively. Partial correlations were used to analyze the relationship between olfaction and anxiety severity. False discovery rate (FDR) correction was used in multi-correlation analyses.

RESULTS

Compared with healthy controls, patients in the GAD group demonstrated odor threshold, discrimination and identification deficits. In the moderate/severe anxiety subgroup, discrimination score was significantly and inversely correlated with the somatic anxiety score (γ=-0.44, q = 0.03), and identification score was significantly and inversely correlated with the HAM-A total score (γ=-0.42, q= 0.04). The TDI score (the sum of threshold, discrimination and identification scores) was significantly and inversely correlated with the somatic (γ=-0.44, q = 0.04) and psychic (γ=-0.45, q = 0.04) anxiety scores in the moderate/severe anxiety subgroup.

CONCLUSION

This study demonstrated the olfactory impairment in patients with GAD and that poorer odor discrimination was correlated with greater severity of somatic anxiety.

Olfactory Impairment in Children and Adolescents With Obsessive-Compulsive Disorder

In this study, we aimed to examine the olfactory function of adolescents with obsessive-compulsive disorder (OCD). We investigated olfactory function of 50 adolescents with OCD and 50 healthy controls (min-max, 12-17 years) by the "Sniffin' Sticks" extended test. OCD and depression symptomatology were assessed with the Maudsley Obsessive-Compulsive Inventory (MOCI) and the Children's Depression Inventory (CDI). Adolescents with OCD had lower olfactory performance than healthy controls. The patients who responded positively to the treatment exhibited performance superior to the patients with partial response and those untreated. All olfactory measurements were significantly inversely correlated with MOCI and CDI total scores and OCD duration. Our results show that OCD has a significant impact on all olfactory tests, and olfactory impairment is related to symptom severity, duration, and course of OCD. The decrease in olfactory function may be a noninvasive state marker for OCD. Further investigations in longitudinal studies are required to confirm our results.

Anatomic alterations across amygdala subnuclei in medication-free patients with obsessive-compulsive disorder

BACKGROUND

The amygdala has been implicated in obsessive-compulsive disorder (OCD), a common, disabling illness. However, the regional distribution of anatomic alterations in this structure and their association with the symptoms of OCD remains to be established.

METHODS

We collected high-resolution 3D T1-weighted images from 81 untreated patients with OCD and no lifetime history of comorbid psychotic, affective or anxiety disorders, and from 95 age- and sex-matched healthy controls. We extracted the volume of the central nucleus of the amygdala (CeA) and the basolateral complex of the amygdala (BLA) and compared them across groups using FreeSurfer 6.0. In exploratory analyses, we evaluated other subnuclei, including the cortical medial nuclei, the anterior amygdaloid area, and the corticoamygdaloid transition area.

RESULTS

Patients with OCD had reduced amygdala volume bilaterally compared with healthy controls (left, p = 0.034; right, p = 0.002). Volume reductions were greater in the CeA (left: -11.9%, p = 0.002; right: -13.3%, p < 0.001) than in the BLA (left lateral nucleus: -3.3%, p = 0.029; right lateral nucleus: -3.9%, p = 0.018; right basal nucleus: -4.1%, p = 0.017; left accessory basal nucleus: -6.5%, p = 0.001; right accessory basal nucleus: -9.3%, p < 0.001). Volume reductions in the CeA were associated with illness duration. Exploratory analysis revealed smaller medial (left: -15.4%, p < 0.001, η2 = 0.101) and cortical (left: -9.1%, p = 0.001, η2 = 0.058; right: -15.4%, p < 0.001, η2 = 0.175) nuclei in patients with OCD compared with healthy controls.

LIMITATIONS

Although the strict exclusion criteria used in the study helped us to identify OCD-specific alterations, they may have limited generalizability to the broader OCD population.

CONCLUSION

Our results provide a comprehensive anatomic profile of alterations in the amygdala subnuclei in untreated patients with OCD and highlight a distinctive pattern of volume reductions across subnuclei in OCD. Based on the functional properties of the amygdala subnuclei established from preclinical research, CeA impairment may contribute to behavioural inflexibility, and BLA disruption may be responsible for altered fear conditioning and the affective components of OCD.

Review: Exteroceptive Sensory Abnormalities in Childhood and Adolescent Anxiety and Obsessive-Compulsive Disorder: A Critical Review

OBJECTIVE

Childhood anxiety and obsessive-compulsive disorder (OCD) are defined by fear, worry, and uncertainty, but there is also evidence that affected children possess exteroceptive sensory abnormalities. These sensory features may often instigate symptoms and cause significant distress and functional impairment. In addition, a purported class of conditions known as "sensory processing disorders" may significantly overlap with childhood anxiety and OCD, which provides further support for a connection between abnormal sensation and fear-based psychopathology.

METHOD

The current review was conducted to synthesize and to critically evaluate the existing research on exteroceptive sensory abnormalities in childhood anxiety and OCD. Because of the paucity of research in this area, studies with adult populations were also briefly reviewed.

RESULTS

The review found significant support for the notion that sensory abnormalities are common in children with anxiety disorders and OCD, but there are significant limitations to research in this area that prevent firm conclusions.

CONCLUSION

Potential avenues for future research on sensory features of pediatric anxiety and OCD are discussed.

Odor sensitivity impairment: a behavioral marker of psychological distress?

OBJECTIVE

Enhanced odor sensitivity, particularly toward threat-related cues, may be adaptive during periods of danger. Research also suggests that chronic psychological distress may lead to functional changes in the olfactory system that cause heightened sensitivity to odors. Yet, the association between self-reported odor sensitivity, objective odor detection, and affective psychopathology is currently unclear, and research suggests that persons with affective problems may only be sensitive to specific, threat-related odors.

METHODS

The current study compared adults with self-reported odor sensitivity that was described as functionally impairing (OSI; n = 32) to those who reported odor sensitivity that was non-impairing (OS; n = 17) on affective variables as well as quantitative odor detection.

RESULTS

Increased anxiety sensitivity, trait anxiety, depression, and life stress, even while controlling for comorbid anxiety and depressive disorders, was found for OSI compared to OS. While OSI, compared to OS, demonstrated only a trend increase in objective odor detection of a smoke-like, but not rose-like, odor, further analysis revealed that increased detection of that smoke-like odor was positively correlated with anxiety sensitivity.

CONCLUSION

These findings suggest that persons with various forms of psychological distress may find themselves significantly impaired by an intolerance of odors, but that self-reported odor sensitivity does not necessarily relate to enhanced odor detection ability. However, increased sensitivity to a smoke-like odor appears to be associated with sensitivity to aversive anxiogenic stimuli. Implications for the pathophysiology of fear- and anxiety-related disorders are discussed.

Preliminary evidence for differential olfactory and trigeminal processing in combat veterans with and without PTSD

Structural and functional changes in the olfactory system are increasingly implicated in the expression of PTSD. Still, very little is known about the neurobiological networks of trauma-related odor sensitivity or how they relate to other objective and subjective measures of olfaction and PTSD. The purpose of this study was to replicate prior findings and further characterize olfactory function in trauma-exposed combat veterans with and without PTSD. We also sought to extend this area of research by exploring the effects of time since the combat-related index trauma (TST) on post-trauma olfactory function, as well as by correlating odor-elicited brain activity to general olfactory ability and odor-elicited PTSD symptoms. Participants included combat veterans with PTSD (CV+PTSD; n = 21) or without any psychiatric disorder (CV-PTSD; n = 27). TST was coded as greater (n = 24) or less (n = 24) than 5 years. There were main effects and/or interaction for PTSD-status and TST across several parameters of olfactory function: odor detection, odor identification, ratings for trauma-related odor intensity and triggered PTSD symptoms, and trauma odor-elicited brain activation. Overall, results suggest olfactory impairment in chronic PTSD, but not necessarily in the earlier stages of the disorder, although some early-stage olfactory findings may be predictive of later olfactory impairment. Results also suggest that trauma-exposed individuals who never develop PTSD may demonstrate olfactory resiliency. Finally, results highlight a potentially unique role of trigeminal odor properties in the olfactory-PTSD relationship.

Altered olfactory processing and increased insula activity in patients with obsessive-compulsive disorder: An fMRI study

Obsessive-compulsive disorder (OCD) patients show increased insula activation to disgust-inducing images compared to healthy controls (HC). We explored whether this disgust reactivity was also present in the olfactory domain by conducting the first fMRI study of olfaction in OCD. Neural activation in response to pleasant and unpleasant odors (vs. unscented air) was investigated in 15 OCD and 15 HC participants using fMRI. OCD participants (vs. HC) had increased left anterior insula activation to unpleasant odors (vs. unscented air), which positively correlated with their disgust sensitivity and ratings of the unpleasantness and intensity of those odors. OCD participants (vs. HC) showed increased activation of caudate nucleus and left anterior and posterior insula to pleasant odors (vs. unscented air), which positively correlated with their OCD symptom severity, trait anxiety, frequency of feeling disgust, and odor intensity ratings. OCD participants had increased anterior insula activation to both pleasant and unpleasant odors, which correlated with their OCD symptoms, anxiety, disgust sensitivity, and frequency of feeling disgust. OCD patients might have a negative cognitive bias and experience all stimuli, regardless of valence, as being more unpleasant than healthy people. These findings further elucidate the neural underpinnings of OCD and may contribute to more effective treatments.

Olfaction in eating disorders and abnormal eating behavior: a systematic review

The study provides a systematic review that explores the current literature on olfactory capacity in abnormal eating behavior. The objective is to present a basis for discussion on whether research in olfaction in eating disorders may offer additional insight with regard to the complex etiopathology of eating disorders (ED) and abnormal eating behaviors. Electronic databases (Medline, PsycINFO, PubMed, Science Direct, and Web of Science) were searched using the components in relation to olfaction and combining them with the components related to abnormal eating behavior. Out of 1352 articles, titles were first excluded by title (n = 64) and then by abstract and fulltext resulting in a final selection of 14 articles (820 patients and 385 control participants) for this review. The highest number of existing literature on olfaction in ED were carried out with AN patients (78.6%) followed by BN patients (35.7%) and obese individuals (14.3%). Most studies were only conducted on females. The general findings support that olfaction is altered in AN and in obesity and indicates toward there being little to no difference in olfactory capacity between BN patients and the general population. Due to the limited number of studies and heterogeneity this review stresses on the importance of more research on olfaction and abnormal eating behavior.

Possible relation between olfaction and anxiety in healthy subjects

AIMS

While olfaction is a sense closely associated with the limbic system and emotions, the relation between emotional status and olfactory functioning has not been well documented. This study aimed to examine the possible effect of anxiety on olfaction in healthy subjects.

METHODS

We investigated the effect of state and trait anxiety on the detection and recognition thresholds for five different odors in 124 healthy subjects (62 men and 62 women, mean age = 27.2 years) using a T&T olfactometer.

RESULTS

While the influences of age, socioeconomic status, IQ, and smoking history on olfaction were not significant, women had a lower recognition threshold for the odor of sweet fruit and a higher detection threshold for that of rotten food as compared with men. Both state and trait anxiety ratings were significantly associated with reduced olfactory ability, especially for identification of rose odor.

CONCLUSIONS

These findings suggest that emotional status affects olfactory functioning in healthy subjects. Our findings may also partly explain the mild olfactory impairment reported in clinical conditions, such as anxiety disorders.

Olfactory functioning in panic disorder

BACKGROUND

The olfactory function in panic disorder (PD) has been scarcely approached in the literature. The purpose of this paper is to study this question by focusing on the olfactory sensitivity (i.e. detection threshold), the reactivity to odors, and the odor awareness in patients suffering from PD.

METHODS

41 patients with PD and 41 healthy controls performed Sniffin׳ Sticks Test (threshold subtest) and completed the Affective Impact of Odors scale (AIO), the Relational Scale of Olfaction (EROL) and the Odor Awareness Scale (OAS). Clinical symptoms rating scales were concurrently obtained.

RESULTS

PD patients showed lower olfactory detection thresholds (i.e. higher sensitivity) along with an enhanced reactivity to odors as well as a greater olfactory awareness compared to the healthy controls. The severity of PD was significantly associated with the olfactory questionnaires ratings, but not with the detection ability. Olfactory measures were intercorrelated in most cases.

LIMITATIONS

i) The results of the olfactory sensitivity are limited to one odorant (phenyl ethyl alcohol) and thus may not be generalizable to other odorants. ii) As comorbid Axis II disorders were not screened, it is not possible to exclude the influence of personality traits in our results. iii) The involvement of the medications in some olfactory outcomes cannot be ruled out.

CONCLUSION

The current findings highlight the importance of the olfactory function in PD as patients appeared to be highly sensitive, reactive and aware of odors. These results are discussed in the light of the common neural substrates involved in the olfactory processing and in the pathophysiology of PD, and also related to the clinical features of this disorder.

Brain structural imaging correlates of olfactory dysfunction in obsessive-compulsive disorder

Olfactory dysfunction has been described in obsessive-compulsive disorder (OCD). Brain regions involved in smell processing partially overlap with structures included in the neurobiological models of OCD, although no previous studies have analyzed the neuroanatomical correlates of olfactory dysfunction in this disorder. The aim of our study was to examine the association between regional gray matter volume, as assessed by a voxel-based morphometry analysis of magnetic resonance images (MRI), and olfactory function, as assessed by the Sniffin' Sticks test (SST). Olfactory function was assessed in 19 OCD patients and 19 healthy volunteers. All participants were also scanned in a 1.5-T magnet to obtain T1-weighted anatomical MRIs, which were pre-processed and analyzed with SPM8. Three different correlation models were used to study the association between regional gray matter volumes and olfactory function in the domains assessed by the SST: detection threshold, discrimination, and identification. OCD patients showed a significant impairment in all the domains assessed by the SST. Voxel-based mapping revealed a positive association in healthy controls between detection threshold and the gray matter content of a left anterior cingulate cortex cluster. In OCD patients, a positive correlation was observed between identification errors and the gray matter volume of the left medial orbital gyrus. In a post hoc analysis, these two gray matter regions were shown to be enlarged in OCD patients. Our findings support the idea that olfactory dysfunction in OCD is associated with volumetric changes in brain areas typically implicated in the neurobiology of the disorder.

A quantitative analysis of facial emotion recognition in obsessive-compulsive disorder

Obsessive-Compulsive Disorder (OCD) is characterized by persistent and unwanted obsessions generally accompanied by ritualistic behaviors or compulsions. Previous research proposed specific disgust facial emotion recognition deficits in patients with OCD. This research however, remains largely inconsistent. Therefore, the results of 10 studies contrasting facial emotion recognition accuracy in patients with OCD (n=221) and non-psychiatric controls (n=224) were quantitatively reviewed and synthesized using meta-analytic techniques. Patients with OCD were less accurate than controls in recognizing emotional facial expressions. Patients were also less accurate in recognizing negative emotions as a whole; however, this was largely due to significant differences in disgust and anger recognition specifically. The results of this study suggest that patients with OCD have difficulty recognizing specific negative emotions in faces and may misclassify emotional expressions due to symptom characteristics within the disorder. The contribution of state-related emotion perception biases to these findings requires further clarification.

Smell and autoimmunity: a comprehensive review

The sense of smell is an ancient sensory modality vital for sampling and perceiving the chemical composition of surrounding environments. Olfaction involves a pathway of biochemical and electrophysiological processes, which allows the conversion of molecular information into sensations. Disturbances in the olfactory function have been investigated mainly in neurological/neurodegenerative disorders such as Alzheimer's and Parkinson's diseases; impaired sense of smell has been associated with depressed mood. Only recently, smell capability was tested in other diseases, particularly autoimmune diseases. Shoenfeld and colleagues opened this chapter showing that patients affected with systemic lupus erythematosus (SLE) have disturbances in their olfactory functions and revealed its association with neuropsychiatric manifestations of the disease. This evidence was confirmed in experimental models and replicated in other SLE populations. The connection between autoimmunity and the sense of smell was lately emphasized by studies on patients with Sjögren's syndrome and in patients with other autoimmune/immune-mediated diseases, such as polydermatomyositis, recurrent spontaneous abortion, and hereditary angioedema. Genetic susceptibility and hormonal and environmental factors may play a role in these conditions. Olfactory receptor gene clusters are located in proximity to key locus of susceptibility for autoimmune diseases such as the major histocompatibility complex, suggesting not only a physic linkage, but a functional association. Nonetheless, gender- and hormone-mediated effects are fundamental in the development of autoimmune diseases. The different connections between smell and autoimmunity, genes and hormones may suggest that this is another tessera of a mosaic which is waiting the answer of Oedipus.

Olfaction in alcohol-dependence: a neglected yet promising research field

Olfaction research deeply renewed the knowledge of the pathophysiological mechanisms involved in various psychopathological states and showed that olfactory deficits might constitute an onset or trait marker in psychiatry. However, while alcohol-dependence is the most wide spread psychiatric disorder and while olfaction might be involved in its development and maintenance, olfactory abilities have been little explored in this population. The central aim of this paper is thus to underline the usefulness of olfaction research in alcohol-dependence. After reviewing the few olfaction studies available, a research agenda will be proposed, identifying the major challenges for future research, and particularly: (1) the identification of the origin, extent and cerebral correlates of olfaction deficits; (2) the links between olfaction and emotional-cognitive deficits, and the use of olfaction to understand the pathomechanisms of alcohol-dependence; (3) the interactions between olfaction and other sensory modalities; (4) the use of olfaction to predict the appearance and intensity of cognitive impairments; (5) the impact of olfaction deficits on everyday life in alcohol-dependence.

Olfactory identification deficits and associated response inhibition in obsessive-compulsive disorder: on the scent of the orbitofronto-striatal model

Olfactory identification ability implicates the integrity of the orbitofrontal cortex (OFC). The fronto-striatal circuits including the OFC have been involved in the neuropathology of Obsessive Compulsive Disorder (OCD). However, only a few studies have examined olfactory function in patients with OCD. The Brief Smell Identification Test (B-SIT) and tests from the Cambridge Neuropsychological Automated Battery (CANTAB) were administered to 25 patients with OCD and to 21 healthy matched controls. OCD patients showed a significant impairment in olfactory identification ability as well as widely distributed cognitive deficits in visual memory, executive functions, attention, and response inhibition. The degree of behavioural impairment on motor impulsivity (prolonged response inhibition Stop-Signal Reaction Time) strongly correlated with the B-SIT score. Our study is the first to indicate a shared OFC pathological neural substrate underlying olfactory identification impairment, impulsivity, and OCD. Deficits in visual memory, executive functions and attention further indicate that regions outside of the orbitofronto-striatal loop may be involved in this disorder. Such results may help delineate the clinical complexity of OCD and support more targeted investigations and interventions. In this regard, research on the potential diagnostic utility of olfactory identification deficits in the assessment of OCD would certainly be useful.

Sensory and motor secondary symptoms as indicators of brain vulnerability

In addition to the primary symptoms that distinguish one disorder from the next, clinicians have identified, yet largely overlooked, another set of symptoms that appear across many disorders, termed secondary symptoms. In the emerging era of systems neuroscience, which highlights that many disorders share common deficits in global network features, the nonspecific nature of secondary symptoms should attract attention. Herein we provide a scholarly review of the literature on a subset of secondary symptoms––sensory and motor. We demonstrate that their pattern of appearance––across a wide range of psychopathologies, much before the full-blown disorder appears, and in healthy individuals who display a variety of negative symptoms––resembles the pattern of appearance of network abnormalities. We propose that sensory and motor secondary symptoms can be important indicators of underlying network aberrations and thus of vulnerable brain states putting individuals at risk for psychopathology following extreme circumstances.