Olfactory dysfunction and its measurement in the clinic and workplace

Reduced Salivary Gustin and Statherin in Long-COVID Cohort with Impaired Bitter Taste

Background/Objectives: Taste dysfunction is a frequent symptom of acute coronavirus disease (COVID)-19 caused by the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). While the majority of those affected reported recovery over time, emerging data suggest that 20-25% of individuals experience persistent taste dysfunction, constituting a common symptom of long COVID. Gustation is mediated by continuously renewing taste bud cells. A balance between the counteracting processes of cell generation and cell death maintains the homeostatic turnover. Sonic hedgehog (SHH) is a morphogenic protein that promotes taste cell proliferation and differentiation. Enzymatic proteins such as gustin modulate the environment around the taste receptors and influence taste perception. Hence, we hypothesized that increased taste cell turnover and reduced taste-related salivary proteins contribute to the taste dysfunction in long COVID. Methods: Unstimulated whole saliva (UWS) was collected from individuals with long COVID experiencing taste dysfunction after obtaining informed consent. The normal control included archived saliva samples catalogued prior to 2019. Taste perception was objectively determined by the waterless empirical taste test. The SHH, gustin, and inflammatory cytokines in UWS were determined with ELISA. The expressions of epithelial and taste-cell-specific markers in cellular saliva were assessed by immunoflurorescence. Results: Impaired bitter taste was the most common dysfunction in the long-COVID cohort. Salivary gustin was significantly lower in those with long COVID and correlated with lower bitter taste score. Cellular saliva showed keratin-10- and small-proline-rich protein-positive epithelial cells as well as SHH-, occluding- and KCNQ1-positive taste cells. Conclusions: Salivary gustin could be a marker for impaired bitter taste in long COVID.

The Impact of Ambient and Wildfire Air Pollution on Rhinosinusitis and Olfactory Dysfunction

PURPOSE OF REVIEW

With increasing industrialization, exposure to ambient and wildfire air pollution is projected to increase, necessitating further research to elucidate the complex relationship between exposure and sinonasal disease. This review aims to summarize the role of ambient and wildfire air pollution in chronic rhinosinusitis (CRS) and olfactory dysfunction and provide a perspective on gaps in the literature.

RECENT FINDINGS

Based on an emerging body of evidence, exposure to ambient air pollutants is correlated with the development of chronic rhinosinusitis in healthy individuals and increased symptom severity in CRS patients. Studies have also found a robust relationship between long-term exposure to ambient air pollutants and olfactory dysfunction. Ambient air pollution exposure is increasingly recognized to impact the development and sequelae of sinonasal pathophysiology. Given the rising number of wildfire events and worsening impacts of climate change, further study of the impact of wildfire-related air pollution is a crucial emerging field.

Olfactory Dysfunction Following Moderate to Severe Traumatic Brain Injury: A Systematic Review and Meta-Analysis

OBJECTIVE

Reports of smell loss following traumatic brain injury (TBI) are a well-documented but understudied phenomenon. Given the broad consequences of olfactory loss, we characterized psychophysical olfactory dysfunction in individuals with moderate to severe TBI using systematic review and meta-analytic methods.

METHODS

Following Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) protocol, five databases (PubMed, EMBASE, Cochrane Library, Web of Science, Scopus) were reviewed for studies investigating olfactory dysfunction in persons with moderate to severe TBI. Of the 5,223 studies reviewed, 19 met our inclusion criteria for the systematic review and 11 met inclusion criteria for meta-analysis. We calculated effect sizes (Hedges' g) to characterize the degree of olfactory dysfunction between patients with moderate to severe TBI and controls.

RESULTS

A total of 951 moderate-severe TBI patients from 19 studies were included in the systematic review, which largely demonstrated poorer olfactory psychophysical performances in this patient population. Meta-analysis demonstrated a large effect size for olfactory dysfunction in moderate-severe TBI relative to healthy controls (g=-2.43, 95%CI: -3.16 < δ<-1.69). The magnitude of the effect was moderated by age and patient sex, with larger effect sizes associated with older age (following exclusion of a pediatric population) and larger compositions of women in the patient group.

CONCLUSION

Moderate to severe TBI is associated with prominent olfactory dysfunction. Significant research gaps remain regarding the mechanism, recovery and natural history of olfactory dysfunction following moderate to severe TBI, which has significant clinical implications for the identification and treatment for those with post-traumatic olfactory dysfunction.

Platelet-rich Plasma in Management of Anosmia (Single Versus Double Injections)

Background

Anosmia is a common problem with a significant impact on quality of life and increased mortality. People with anosmia may not be able to fully taste foods and may lose interest in eating. This can lead to weight loss or malnutrition. Anosmia can also lead to depression because it may impair one's ability to smell or taste pleasurable foods. Platelet-rich plasma (PRP) is an autologous biologic product with anti-inflammatory and neuroprotective effects. This prospective study evaluated the role of PRP on olfactory neuroregeneration in patients with anosmia and compare the results of single and double injections.

Methods

54 patients were included in the study who had olfactory loss greater than 6 months in duration, no evidence of sinonasal inflammatory disease, and no improvement with olfactory training and topical steroids. 27 patients received a single intranasal injection of PRP into the mucosa of the olfactory cleft and 27 patients received a double injections with 3 weeks interval between them. The Q-Sticks Test was administered at the beginning of the study and at 1 and 3 months.

Results

All patients reported a subjective improvement of their smell shortly after injection but then stabilized. At 3-month post-treatment, 16 patients improved significantly after single injection and 19 patients improved significantly after double injections. There were no adverse outcomes from intranasal PRP injections.

Conclusion

PRP appears safe for use in the treatment of olfactory loss, and preliminary data suggest possible efficacy, especially for those with persistent loss. Further studies will help determine optimal frequency and duration of use.

Chemosensory Dysfunction Induced by Environmental Pollutants and Its Potential As a Novel Neurotoxicological Indicator: A Review

Air pollution composed of the complex interactions among particular matter, chemicals, and pathogens is an emerging and global environmental issue that closely correlates with a variety of diseases and adverse health effects, especially increasing incidences of neurodegenerative diseases. However, as one of the prevalent health outcomes of air pollution, chemosensory dysfunction has not attracted enough concern until recently. During the COVID-19 pandemic, multiple scientific studies emphasized the plausibly essential roles of the chemosensory system in the airborne transmission airway of viruses into the human body, which can also be utilized by pollutants. In this Review, in addition to summarizing current progress regarding the contributions of traditional air pollutants to chemosensory dysfunction, we highlight the roles of emerging contaminants. We not only sum up clarified mechanisms, such as inflammation and apoptosis but also discuss some not yet completely identified mechanisms, e.g., disruption of olfactory signal transduction. Although the existing evidence is not overwhelming, the chemosensory system is expected to be a useful indicator in neurotoxicology and neural diseases based on accumulating studies that continually excavate the deep link between chemosensory dysfunction and neurodegenerative diseases. Finally, we argue the importance of studies concerning chemosensory dysfunction in understanding the health effects of air pollution and provide comments for some future directions of relevant research.

Olfactory shifts linked to postpartum depression

Postpartum Depression (PPD) is the most common non-obstetric complications associated with childbearing, but currently has poor diagnostic regimes. Sensory symptoms of PPD are understudied, particularly with regard to the sense of olfaction. The present study addresses this research gap by assessing differences in olfactory abilities between 39 depressed mothers, who were within the perinatal period (i.e., during pregnancy and up to 1-year post pregnancy) and assessed with Edinburgh Postnatal Depression Scale, and their case-matched healthy volunteers. The assessments include two olfactory testing sessions conducted 4-weeks apart, each comprising a standard odour detection threshold test (i.e., Snap & Sniff Olfactory Test System), and intensity and valence ratings for 3 “pleasant” and 3 “unpleasant” odorants. The results revealed no difference between patients (M = 5.6; SE = 0.3) and control group (M = 5.7; SE = 0.4) in terms of olfactory detection threshold. However, the patients group perceived the 3 “unpleasant” odours as significantly less pleasant (p < 0.05), and 2 odorants (1 “pleasant” and 1 “unpleasant”) as less intense. Additionally, these results did not appear to be significantly interacted with the individual’s perinatal stage. The present study is the first to evaluate associations between olfactory function and PPD. Findings from the study suggest that, while PPD has little effect on the early stages of olfactory processing, these conditions may have stronger influence on higher-order olfactory perception, including both hedonic and intensity perception. These novel findings add knowledge to sensory symptoms of PPD.

Clinical Implications of Psychophysical Olfactory Testing: Assessment, Diagnosis, and Treatment Outcome

Purpose of Review

Olfactory dysfunction dramatically impairs quality of life with a prevalence of 20% in the general adult population. Psychophysical olfactory testing has been widely used to evaluate the ability to smell due to its validated utility and feasibility in clinic. This review summarizes the current literature regarding psychophysical olfactory testing and the clinical relevance of the olfactory testing with different components. Furthermore, the review highlights the diagnosis and treatment value of olfactory subtests in patients with olfactory dysfunction.

Recent Findings

With the accumulation of studies of psychophysical olfactory testing in olfactory disorders, the clinical relevance of olfactory testing with different components is expanding. Different olfactory domains present with distinct olfactory processing and cortical activity. Psychophysical assessment of olfaction with three domains reveals different levels of olfactory processing and might assist with analyzing the pathophysiologic mechanism of the various olfactory disorders. Furthermore, olfactory thresholds provided the largest amount of non-redundant information to the olfactory diagnosis. Sinonasal olfactory dysfunction and non-sinonasal-related olfactory dysfunction are emerging classifications of smell disorders with certain characteristics of olfactory impairment and different responses to the therapy including steroids, sinus surgery, and olfactory training.

Summary

These recent advancements should promote the understanding of psychophysical olfactory testing, the association between individual subcomponents and neurophysiological processes, and pave the way for precision assessment and treatment of the olfactory dysfunction.

Olfactory Performance among Hospital Residents

Introduction  Smell plays an important role in the maintenance of health and quality of life of the general population. Health workers with olfactory impairment may not be able to help diagnose certain diseases, and subsequently increase the risk of hazardous events and mortality among those affected. ‘Odor learning’ requires repeated experiences with different smells to develop a discriminatory ability, and this is a process that takes years. Because of that, physicians of certain medical specialities have better odor detection than others.

Objective  To study the olfactory performance and associated factors of otorhinolaryngology residents compared with residents of different medical specialities in a representative sample of a tertiary hospital.

Methods  The University of Pennsylvania Smell Identification Test (UPSIT) was used to compare olfactory performance. Clinical and epidemiological data were collected among 42 hospital residents.

Results  Otorhinolaryngology residents presented an average UPSIT score of 35.0, and the other residents, a score of 32.8 ( p  = 0.02) Of all the residents, 40.5% showed some grade of olfactory impairment. Half of the females students in the first year of residency showed olfactory dysfunction. The multivariate analyses found age ( p  = 0.03; 95% confidence interval for β = 0.33) to be an independent predictor of the UPSIT score.

Conclusion  The present study demonstrated that otorhinolaryngology residents have greater olfactory capacity compared with other residents. Future studies should explore the relevant factors of olfactory impairment and its impact on quality of life in this population.

Impact of the smell loss on the quality of life and adopted coping strategies in COVID-19 patients

Purpose

To study the impact of smell loss on quality of life in patients with Coronavirus Disease 2019 (COVID-19), and assess the importance of olfaction before and after the loss of smell. In addition, to assess the impact of smell loss on psychological well-being and distress, and to assess coping strategies used by COVID-19 patients with smell loss.

Methods

This study was a cross-sectional study. A total of 487 COVID-19 positive patients with anosmia were recruited. All participants filled in the validated Multi-Clinic Smell and Taste Questionnaire, and the validated General Well-being Schedule.

Results

Negative impacts of smell loss, associated risks, interference with daily activities, and deterioration in well-being were common. The importance of the sense of smell was evaluated (In relation to other senses) as higher in the period after the loss than before the loss (p < 0.001). All aspects of health-related QOL are statistically significant (p < 0.001), with the exception of financial security and friendship, which are not statistically significant (p = 0.129, p = 0.334), respectively. Psychological well-being was negatively affected, and the use of both problem- and emotion-focused strategies was common.

Conclusion

COVID-19 Patients with loss of smell have significant reductions in health-related QOL. Their loss of smell directly affects daily activities related to the olfactory function. Therefore, priority should be given to diagnose and treat the loss of smell. Patients who have recently developed smell loss may be offered a combination of the problem- and emotion-focused strategies to cope with their condition.

Clinical assessment of olfactory function

Approximately 5% of the general population is affected by functional anosmia with approximately additional 15% exhibiting decreased olfactory function. Many of these individuals ask for help. Because the subjective rating of olfactory function is biased, assessment of olfactory function is important. Olfactory measurements are needed for patient counseling and the tracking of changes in the sense of smell over time. The present review provides an overview of frequently used psychophysical tests for olfactory function, discusses differences between threshold and suprathreshold aspects of olfactory function, and gives examples on how to apply psychophysical tests.

Objective evaluation of odor loss in COVID-19 and other suspected cases

Introduction

COVID-19 is a pandemic disease known with one of the symptoms is sudden onset anosmia. This symptom sometimes may be the only sign of the disease, therefore it must be research widely.

Objective

We aim to evaluate odor dysfunction in COVID-19 patients objectively and safely without any risk of transmitting the disease.

Methods

The odor threshold test was performed on 105 patients hospitalized at the XXXX Training and Research Hospital on the COVID-19 pandemic service before any treatment began. Odor threshold was tested using a modification of the Connecticut Chemosensory Clinical Research Center olfactory function test. COVID-19 signs and symptoms, PCR test results, thorax computed tomography (CT) findings, and length of hospital stay were recorded. Odor tests were scored between 0–8, 0–1 anosmia, 2–3 severely hyposmia, 4 moderate hyposmia, 5 mild hyposmia, 6 and above normosmia.

Results

Forty-one (39%) of the 105 patients were diagnosed with COVID-19 after the PCR results. Patients with an odor threshold score < 5 were classified as “Smell-Impaired Group”, patients with an odor threshold score ≥ 5 were placed in “Smell Intact Group”. The incidence of female patients in smell-impaired group was significantly higher (p ˂ 0.05). The proportion of patients who were PCR-positive for COVID-19 in smell-impaired group was significantly higher (p ˂ 0.05) than in smell intact group. Among patients with an odor threshold score from 0 to 1 (anosmic; n = 15), 12 (80%) demonstrated PCR positivity (p < 0.0001).

Conclusion

Anosmia can be predictive for coronavirus disease. Odor threshold test can be helpful for diagnosis.

Altered Olfactory Function in Patients with Systemic Lupus Erythematosus

Background

The objective of this study was to detect the level of olfactory function in patients with systemic lupus erythematosus (SLE) and to explore the relationship between impaired olfactory function and anti-ribosomal P protein antibody (ARPA), disease duration, and age.

Material/Methods

The level of olfactory function in 65 patients with SLE and 50 healthy participants was detected using the Connecticut Chemosensory Clinical Research Center (CCCRC) method; serum ARPA levels in SLE patients and the healthy control group were detected by enzyme-linked immunosorbent assay (ELISA).

Results

CCCRC scores in the active SLE group was lower than that in the inactive SLE and healthy control groups (P<0.01). In SLE patients, the CCCRC scores of ARPA-positive patients were lower than those of ARPA-negative patients (P<0.01). A negative correlation was discovered between CCCRC scores and ARPA serum levels in SLE patients. Multiple linear regression analyses showed a correlation among the CCCRC score, age, and ARPA.

Conclusions

Olfactory dysfunction was found in patients with active SLE; which correlated with SLE disease activity and ARPA levels.

Fast Screening of Olfactory Function Using the Q-Sticks Test

OBJECTIVES

Classical, longer olfactory tests are associated with difficulties in everyday practice. The aim of this study was to investigate the clinical utility of the Q-Sticks test within the context of a multicenter study.

METHODS

A total of 333 subjects, aged between 12 and 88 years, completed a 3-item Q-Sticks test and a longer Sniffin' Sticks identification test. We analyzed the sensitivity and specificity of the test results for different cutoffs for anosmia and hyposmia.

RESULTS

Our study showed that the test can be used on subjects aged 12 years and older, regardless of their sex. The data indicated a test sensitivity and specificity of 91.8 and 92%, respectively, with a score of 2 taken as a cutoff for olfactory dysfunction. Conversely, normal olfactory function can be declared with high probability with a score of 3 in the Q-Sticks test.

CONCLUSION

We reconfirmed that the Q-Sticks test is a good screening tool for everyday medical practice and in laboratory settings, although it has to be kept in mind that the test can produce false-negative results at a score of 3. The test was relatively sensitive to anosmia and differences between normosmic and hyposmic/anosmic patients.

Neural Dynamics of Olfactory Perception: Low- and High-Frequency Modulations of Local Field Potential Spectra in Mice Revealed by an Oddball Stimulus

Recent brain connectome studies have evidenced distinct and overlapping brain regions involved in processing olfactory perception. However, neural correlates of hypo- or anosmia in olfactory disorder patients are poorly known. Furthermore, the bottom-up and top-down processing of olfactory perception have not been well-documented, resulting in difficulty in locating the disease foci of olfactory disorder patients. The primary aim of this study is to characterize the bottom-up process of the neural dynamics across peripheral and central brain regions in anesthetized mice. We particularly focused on the neural oscillations of local field potential (LFP) in olfactory epithelium (OE), olfactory blub (OB), prefrontal cortex (PFC), and hippocampus (HC) during an olfactory oddball paradigm in urethane anesthetized mice. Odorant presentations evoked neural oscillations across slow and fast frequency bands including delta (1-4 Hz), theta (6-10 Hz), beta (15-30 Hz), low gamma (30-50 Hz), and high gamma (70-100 Hz) in both peripheral and central nervous systems, and the increases were more prominent in the infrequently presented odorant. During 5 s odorant exposures, the oscillatory responses in power were persistent in OE, OB, and PFC, whereas neural oscillations of HC increased only for short time at stimulus onset. These oscillatory responses in power were insignificant in both peripheral and central regions of the ZnSO4-treated anosmia model. These results suggest that olfactory stimulation induce LFP oscillations both in the peripheral and central nervous systems and suggest the possibility of linkage of LFP oscillations in the brain to the oscillations in the peripheral olfactory system.

Microglial involvement in the development of olfactory dysfunction

Olfactory impairment is the most common clinical manifestation among the elderly, and its prevalence increases sharply with age. Notably, growing evidence has shown that olfactory dysfunction is the first sign of neurodegeneration, indicating the importance of olfactory assessment as an early marker in the diagnosis of neurological disorders. In this review, we describe the nature of olfactory dysfunction and the advantage of using animal models in olfaction study, and we include a brief introduction to olfactory behavior tests widely used in this field. The contribution of microglia in the neurodegenerative processes including olfactory impairment is then discussed to provide a comprehensive description of the physiopathological role of interactions between neurons and microglia within the olfactory system.

Severe Urban Outdoor Air Pollution and Children's Structural and Functional Brain Development, From Evidence to Precautionary Strategic Action

According to the latest estimates, about 2 billion children around the world are exposed to severe urban outdoor air pollution. Transdisciplinary, multi-method findings from epidemiology, developmental neuroscience, psychology, and pediatrics, show detrimental outcomes associated with pre- and postnatal exposure are found at all ages. Affected brain-related functions include perceptual and sensory information processing, intellectual and cognitive development, memory and executive functions, emotion and self-regulation, and academic achievement. Correspondingly, with the breakdown of natural barriers against entry and translocation of toxic particles in the brain, the most common structural changes are responses promoting neuroinflammation and indicating early neurodegenerative processes. In spite of the gaps in current scientific knowledge and the challenges posed by non-scientific issues that influence policy, the evidence invites the conclusion that urban outdoor air pollution is a serious threat to healthy brain development which may set the conditions for neurodegenerative diseases. Such evidence supports the perspective that urgent strategic precautionary actions, minimizing exposure and attenuating its effects, are needed to protect children and their brain development.

Gross Olfaction Before and After Laparoscopic Gastric Bypass

BACKGROUND

Obesity leads to olfaction alterations, and this can further impact food choices, appetite, and nutritional status. Bariatric procedures induce weight loss and change in taste and smell perception, but more information is needed, especially using objective olfaction tests.

METHODS

A prospective study was conducted during 6 months, with candidates to laparoscopic gastric bypass at a single institution. A preoperative nasofibroscopy and gross smell identification test (The Pocket Smell Test ®) were performed in those meeting the inclusion criteria. After 6 months, a new test was performed, and the primary objective was to determine if there was an improvement in the olfaction score. Weight loss and comorbidities improvement were also analyzed.

RESULTS

From the 30 patients with morbid obesity enrolled, 21 met the inclusion criteria and ENT evaluation. At baseline, 42.8% of patients scored 3 points, 53.3% scored 2 points, and 4.7% scored 1 point. After 6 months, there was a -81.1% of change. Seventeen patients scored 3 points (p = 0.002 vs initial) and two scored 2 points (p = 0.006 vs initial). There were no patients with less than 2 points. Weight and comorbidities had a significant improvement as well.

CONCLUSION

Laparoscopic gastric bypass improves the olfaction scores of the Pocket Smell Test in morbidly obese patients 6 months after their procedure. More complex tests can be used in candidates to bariatric surgery if low scores are detected initially. Other causes of olfaction dysfunctions should be determined if there is no improvement after weight loss.

A Pilot Study of the Snap & Sniff Threshold Test

OBJECTIVES

The Snap & Sniff^® Threshold Test (S&S) has been recently developed to determine the olfactory threshold. The aim of this study was to further evaluate the validity and test-retest reliability of the S&S.

METHODS

The olfactory thresholds of 120 participants were determined using both the Smell Threshold Test (STT) and the S&S. The participants included 30 normosmic volunteers and 90 patients (60 hyposmic, 30 anosmic). The normosmic participants were retested using the STT and S&S at an intertest interval of at least 1 day.

RESULTS

The mean olfactory threshold determined with the S&S was -6.76 for the normosmic participants, -3.79 for the hyposmic patients, and -2 for the anosmic patients. The olfactory thresholds were significantly different across the 3 groups ( P < .001). Snap & Sniff-based and STT-based olfactory thresholds were correlated weakly in the normosmic group (correlation coefficient = 0.162, P = .391) but more strongly correlated in the patient groups (hyposmic: correlation coefficient = 0.376, P = .003; anosmic: correlation coefficient = 1.0). The test-retest correlation for the S&S-based olfactory thresholds was 0.384 ( P = .036).

CONCLUSION

Based on validity and test-retest reliability, we concluded that the S&S is a proper test for olfactory thresholds.

Olfactory function in systemic lupus erythematosus and systemic sclerosis. A longitudinal study and review of the literature

BACKGROUND/PURPOSE

To evaluate olfactory function in systemic lupus erythematosus (SLE), systemic sclerosis (SSc) and healthy controls over a 2-year period, and to determine the association of olfactory dysfunction with age, disease activity, disease damage, treatment, anxiety and depression symptoms and limbic structures volumes.

METHODS

Consecutive SLE and SSc patients were enrolled in this study. Clinical, laboratory disease activity and damage were assessed according to diseases specific guidelines. Olfactory functions were evaluated using the Sniffin' Sticks test (TDI). Volumetric magnetic resonance imaging (MRI) was obtained in a 3T Phillips scanner. Amygdalae and hippocampi volumes were analyzed using FreeSurfer® software.

RESULTS

We included 143 SLE, 57 SSc and 166 healthy volunteers. Olfactory dysfunction was observed in 78 (54.5%) SLE, 35 (59.3%) SSc patients and in 24 (14.45%) controls (p<0.001) at study entry. SLE and SSc patients had significantly lower mean in all three phases (TDI) of the olfactory assessment when compared with healthy volunteers. In SLE, the presence of olfactory dysfunction was associated with older age, disease activity, higher anxiety and depression symptoms score, smaller left hippocampus volume, smaller left and right amygdalae volume and the presence of anti-ribosomal P (anti-P) antibodies. In SSc the presence of olfactory impairment was associated with older age, disease activity, smaller left and right hippocampi volumes and smaller right amygdala volume. Olfactory function was repeated after a 2-year period in 90 SLE, 35 SSc and 62 controls and was stable in all three groups.

CONCLUSION

Both SLE and SSc patients with longstanding disease had significant reduction in all stages of TDI that maintained stable over a 2-year period. Olfactory dysfunction was associated with age, inflammation and hippocampi and amygdalae volumes. In SLE, additional association with anti-P, anxiety and depression symptoms was observed.

Association of 2,4-dichlorophenol urinary concentrations and olfactory dysfunction in a national sample of middle-aged and older U.S. adults

Olfaction is a key sensory mechanism in humans. Deficits in this chemosensory function have wide-ranging impacts on overall health and quality of life. This study examines the role of environmental phenols as risk factors for olfactory dysfunction among a random sample of 839 middle-aged and older U.S. adults. Olfactory function assessment was carried out using a short 8-item test, scores on which were used to classify subjects into normal or impaired olfactory function groups. Logistic regression models were used to test for associations between olfactory impairment and creatinine-adjusted urinary levels of 8 common environmental phenols, adjusting for potentially confounding covariates. A statistically significant association between 2,4-dichlorophenol levels and olfactory impairment (OR = 1.02 [95 % CI: (1.003, 1.04)]; p = 0.02) was found. 2,4-dichlorophenol is a hazardous pollutant with widespread exposure via industrial and indoor air pollution, diet, and the use of pesticides and herbicides. This study is the first to reveal its role in olfactory impairment.

Correlation between the availability of dopamine transporter and olfactory function in healthy subjects

OBJECTIVES

Olfactory dysfunction in Parkinson's disease is usually prodromal to other symptoms. In this study, we aimed to explore the association of olfactory function with the availabilities of striatal dopamine transporter (DAT) in healthy subjects.

METHODS

Data used in the preparation of this article were obtained from Parkinson's Progression Markers Initiative database ( www.ppmi-info.org/data ). The study population consisted of healthy controls with screening ¹²³I-FP-CIT single photon emission tomography (SPECT). University of Pennsylvania Smell Identification Test (UPSIT) was assessed to evaluate the olfactory function.

RESULTS

Totally, 181 healthy subjects (117 male, 64 female) with ¹²³I-FP-CIT SPECT data were included in this study. Specific binding ratios (SBRs) of the caudate nucleus (rho = -0.4217, p < 0.0001), putamen (rho = -0.2292, p = 0.0019), and striatum (rho=-0.3425, p < 0.0001) showed a reduction with ageing. SBRs of the caudate nucleus, putamen, and striatum were positively correlated with UPSIT (rho = 0.3716, p < 0.0001; rho = 0.3655, p < 0.0001; rho = 0.3880, p < 0.0001). After controlling for age by partial correlation, SBRs of the caudate nucleus, putamen, and striatum showed an influence on UPSIT (rho = 0.3288, p < 0.0001; rho = 0.3374, p < 0.0001; rho = 0.3511, p < 0.0001).

CONCLUSION

Olfactory function is associated with the availability of striatal DAT independent of age in healthy subjects.

KEY POINTS

• Olfactory dysfunction in Parkinson's disease is prodromal to other symptoms. • The availability of dopamine transporter showed a reduction with ageing. • Olfactory function is associated with the availability of dopamine transporter.

SMELL-S and SMELL-R: Olfactory tests not influenced by odor-specific insensitivity or prior olfactory experience

Smell dysfunction is a common and underdiagnosed medical condition that can have serious consequences. It is also an early biomarker of neurodegenerative diseases, including Alzheimer's disease, where olfactory deficits precede detectable memory loss. Clinical tests that evaluate the sense of smell face two major challenges. First, human sensitivity to individual odorants varies significantly, so test results may be unreliable in people with low sensitivity to a test odorant but an otherwise normal sense of smell. Second, prior familiarity with odor stimuli can bias smell test performance. We have developed nonsemantic tests for olfactory sensitivity (SMELL-S) and olfactory resolution (SMELL-R) that use mixtures of odorants that have unfamiliar smells. The tests can be self-administered by healthy individuals with minimal training and show high test-retest reliability. Because SMELL-S uses odor mixtures rather than a single molecule, odor-specific insensitivity is averaged out, and the test accurately distinguished people with normal and dysfunctional smell. SMELL-R is a discrimination test in which the difference between two stimulus mixtures can be altered stepwise. This is an advance over current discrimination tests, which ask subjects to discriminate monomolecular odorants whose difference in odor cannot be quantified. SMELL-R showed significantly less bias in scores between North American and Taiwanese subjects than conventional semantically based smell tests that need to be adapted to different languages and cultures. Based on these proof-of-principle results in healthy individuals, we predict that SMELL-S and SMELL-R will be broadly effective in diagnosing smell dysfunction.

Smoking and olfactory dysfunction: A systematic literature review and meta-analysis

OBJECTIVES/HYPOTHESIS

A systematic review and meta-analysis of the literature was undertaken, examining the association between tobacco smoking and olfactory function in humans, utilizing PubMed and Web of Science (1970-2015) as data sources.

STUDY DESIGN

Systematic literature review and meta-analysis.

METHODS

This database review of studies of smoking and olfaction, with a focus on identifying high-quality studies (based on modified versions of the Newcastle-Ottawa Scale), used validated olfactory tests among the generally healthy population.

RESULTS

We identified 11 studies meeting inclusion criteria. Of 10 cross-sectional studies, two were excluded from meta-analysis because the cohorts they studied were included in another article in the review. In meta-analysis, current smokers had substantially higher odds of olfactory dysfunction compared to never smokers (odds ratio [OR] = 1.59, 95% confidence interval [CI] = 1.37-1.85). In contrast, former smokers were found to have no difference in risk of impaired olfaction compared to never smokers (OR = 1.05, 95% CI = 0.91-1.21). The single longitudinal study reviewed found a trend toward increased risk of olfactory decline over time in ever smokers; this trend was stronger in current as compared to former smokers.

CONCLUSIONS

Current smoking, but not former smoking, is associated with significantly increased risk of olfactory dysfunction, suggesting that the effects of smoking on olfaction may be reversible. Future studies that prospectively evaluate the impact of smoking cessation on improvement in olfactory function are warranted.

LEVEL OF EVIDENCE

N/A. Laryngoscope, 127:1753-1761, 2017.

Fine particulate matter exposure and olfactory dysfunction among urban-dwelling older US adults

OBJECTIVES

The olfactory nerve is anatomically susceptible to injury from pollution in inspired air, but there are no large-scale epidemiologic studies investigating this relationship.

METHODS

Cross-sectional study using data from the National Social Life, Health, and Aging Project, a representative sample of home-dwelling US adults age 57-85 years. Olfactory function was tested using a validated 5-item odor identification test (Sniffin' Sticks). Exposure to fine particulate matter (PM_2.5) at each respondent's home was estimated as 1-12 month moving averages prior to olfactory assessment using validated spatio-temporal models.

RESULTS

Olfactory dysfunction was significantly associated with PM_2.5 exposures averaged over 3-12 months in urban-dwelling respondents. The strongest effect was for 6 month average exposure (per 1-IQR increase in PM_2.5: OR 1.28, 95% CI 1.05, 1.55) adjusting for age, gender, race/ethnicity, education, cognition, comorbidity, smoking, and the season. Interestingly, the most deleterious effects were observed among the youngest respondents, 57-64 years old, and those living in the northeast and south.

CONCLUSIONS

We show for the first time that air pollution exposure is associated with poor olfaction among urban-living, older US adults.

Effects of Ambient Air Pollution Exposure on Olfaction: A Review

BACKGROUND

Olfactory dysfunction affects millions of people worldwide. This sensory impairment is associated with neurodegenerative disease and significantly decreased quality of life. Exposure to airborne pollutants has been implicated in olfactory decline, likely due to the anatomic susceptibility of the olfactory nerve to the environment. Historically, studies have focused on occupational exposures, but more recent studies have considered effects from exposure to ambient air pollutants.

OBJECTIVES

To examine all relevant human data evaluating a link between ambient pollution exposure and olfaction and to review supporting animal data in order to examine potential mechanisms for pollution-associated olfactory loss.

METHODS

We identified and reviewed relevant articles from 1950 to 2015 using PubMed and Web of Science and focusing on human epidemiologic and pathophysiologic studies. Animal studies were included only to support pertinent data on humans. We reviewed findings from these studies evaluating a relationship between environmental pollutant exposure and olfactory function.

RESULTS

We identified and reviewed 17 articles, with 1 additional article added from a bibliography search, for a total of 18 human studies. There is evidence in human epidemiologic and pathologic studies that increased exposure to ambient air pollutants is associated with olfactory dysfunction. However, most studies have used proxies for pollution exposure in small samples of convenience. Human pathologic studies, with supporting animal work, have also shown that air pollution can contact the olfactory epithelium, translocate to the olfactory bulb, and migrate to the olfactory cortex. Pollutants can deposit at each location, causing direct damage and disruption of tissue morphology or inducing local inflammation and cellular stress responses.

CONCLUSIONS

Ambient air pollution may impact human olfactory function. Additional studies are needed to examine air pollution-related olfactory impacts on the general population using measured pollution exposures and to link pollution exposure with olfactory dysfunction and related pathology. Citation: Ajmani GS, Suh HH, Pinto JM. 2016. Effects of ambient air pollution exposure on olfaction: a review. Environ Health Perspect 124:1683-1693; http://dx.doi.org/10.1289/EHP136.

Cross-Culturally Modified University of Pennsylvania Smell Identification Test for a Turkish Population

Background

The University of Pennsylvania Smell Identification Test (UPSIT) is a well-developed and popular olfactory test, which has been validated in various populations. However, there was only one study in a Turkish population, and this study indicated that the North American version of the UPSIT was not enough to evaluate the olfactory functions of Turkish population. So, we developed a cross-cultural adaptation of the UPSIT, the UPSIT-Turkish (UPSIT-T). Thus, the goal of this study was to investigate the applicability of the UPSIT-T in healthy Turkish subjects.

Material and Methods

The study included 51 healthy individuals who reported having normal olfactory function. The participants were administered the North American version of the UPSIT firstly, and then, after a day UPSIT-T was applied to the participants. The results of two smell tests were compared, and the applicability of UPSIT-T was evaluated.

Results

The mean (standard deviation) value for correctly identified odors was 27.2 ± 5.7 (range, 14–38) with the UPSIT application, whereas the mean (standard deviation) value for correctly identified odors was 35.9 ± 3.1 for UPSIT-T. There was a statistically significant increase in the scores of the participants when UPSIT-T was performed (p < 0.001). The identification rates of 10 test odorants were <80% for our study group, and 2 of 10 were <70% for the UPSIT-T.

Conclusion

The UPSIT-T modification is an adequate olfactory test for clinical use in a Turkish population.

A Pilot Study of the Self-Administered Computerized Olfactory Testing System

Background

The Self-Administered Computerized Olfactory Testing System (SCOTS) was developed recently to perform the olfactory threshold test under computer control. The aim of this study was to evaluate the validity and test-retest reliability of the SCOTS.

Methodology

A total of 180 subjects were tested for olfactory thresholds using an odor detection threshold test and the SCOTS. There were 60 normosmic volunteers, 60 hyposmic patients, and 60 anosmic patients. Among them, 30 normosmic subjects were retested with the SCOTS at least 1 day after the first test occasion. The olfactory threshold test and retest results from the SCOTS were compared.

Results

The mean olfactory threshold attained from the SCOTS was -5.48 for normosmic subjects, -3.18 for hyposmic patients, and -2 for anosmic patients. The olfactory thresholds among the normosmic, hyposmic, and anosmic patients were significantly different (p < .001). The correlation coefficient between the olfactory thresholds of an odor detection threshold test and the SCOTS was 0.809 (p < .001). The test-retest correlation for the SCOTS-based olfactory thresholds was strong (r = 0.671; p < .001).

Conclusion

Our results show that on the basis of its validity and test-retest reliability, the SCOTS was appropriate for self-administered tests of the olfactory threshold.

Olfactory loss after uvulopalatopharyngoplasty: a report of two cases with review of the literature

Uvulopalatopharyngoplasty (UPPP) has been a popular surgical method for treating obstructive sleep apnea syndrome since it was introduced in the early 1980s. Olfactory loss has been reported as a rare side effect in several cases. However, the olfactory test results and the prognosis were not mentioned in these cases. We present two patients who complained of loss of olfactory function after UPPP. Their olfactory function was evaluated by the phenyl ethyl alcohol odor detection threshold test and the University of Pennsylvania Smell Identification Test. After treatment with steroid and zinc salt, their olfactory function was improved but not recovered completely.

Quantitative measurement of odor detection thresholds using an air dilution olfactometer, and association with genetic variants in a sample of diverse ancestry

Genetic association studies require a quantitative and reliable method for odor threshold assessment in order to examine the contribution of genetic variants to complex olfactory phenotypes. Our main goal was to assess the feasibility of a portable Scentroid air dilution olfactometer for use in such studies. Using the Scentroid SM110C and the SK5 n-butanol Sensitivity Kit (IDES Canada Inc.), n-butanol odor thresholds were determined for 182 individuals of diverse ancestry (mean age: 20.4 ± 2.5 years; n = 128 female; n = 54 male). Threshold scores from repeat participants were used to calculate a test–retest reliability coefficient, which was statistically significant (r = 0.754, p < 0.001, n = 29), indicating that the Scentroid provides reliable estimates of odor thresholds. In addition, we performed a preliminary genetic analysis evaluating the potential association of n-butanol odor thresholds to six single-nucleotide polymorphisms (SNPs) putatively involved in general olfactory sensitivity (GOS). The results of multiple linear regression analysis revealed no significant association between the SNPs tested and threshold scores. However, our sample size was relatively small, and our study was only powered to identify genetic markers with strong effects on olfactory sensitivity. Overall, we find that the Scentroid provides reliable quantitative measures of odor detection threshold and is well suited for genetic studies of olfactory sensitivity.

Sadness might isolate you in a non-smelling world: olfactory perception and depression

Major depressive disorder (MDD) occurs with a high prevalence among mental illnesses. MDD patients experience sadness and hopelessness, with blunted affective reactivity. However, such depressive episodes are also key symptoms in other depressive disorders, like Bipolar Disorder (BPD) or Seasonal Affective Disorder (SAD). Moreover, depressive symptoms can also be found in healthy individuals, but are experienced as less severe or for a shorter duration than in patients. Here, it is aimed to summarize studies investigating odor perception in depression, including depressive states in healthy individuals and patient populations. Odor perception in depression has been assessed with psychophysical methods (olfactory sensitivity, odor identification, and discrimination), and odor ratings (intensity, emotional valence, familiarity). In addition, some studies investigated affective reactions to odors, and physiological and anatomical correlates of odor perception in depression. The summary reveals that MDD is associated with reduced olfactory sensitivity. However, odor identification and discrimination scores seem to be unaffected by depression. The reduced olfactory sensitivity might be associated with a reduced ability to encode olfactory information and a reduced volume of the olfactory bulb. While similar processes seem to occur in healthy individuals experiencing depressive states, they have not been observed in BPD or SAD patients. However, in order to conclude that the reduced olfactory sensitivity is directly linked to depression, it is suggested that studies should implement control measures of cognitive performances or perceptual abilities in other stimulus modalities. It is concluded that the reduced olfactory performance in MDD patients seems to be disorder-, modality-, and test-specific, and that the application of an appropriate olfactory and cognitive test-battery might be highly useful in the differential diagnosis of MDD.

Connecticut (CCCRC) Olfactory Test: Normative Values in 426 Healthy Volunteers

Application of Connecticut Chemosensory Clinical Research Center (CCCRC) olfactory test to healthy Turkish volunteers, obtain normative data set and analyse the role of age, sex and smoking on olfactory scores. The present study was conducted at Bezmialem Vakif University, Department of Otorhinolaryngology. Total of 426 healthy volunteers were subjected to CCCRC olfactory test which consists of n-butanol smell threshold test and smell identification test. Olfactory function score was assessed (0: worst score; 7: best score) and mean scores were calculated. Mean age was (36.7 ± 11.1; range, 17-68). 46.2 % of the subjects were male and 53.8 % were female; 37.1 % were smokers and 62.9 % were non-smokers. Mean n-butanol threshold score was 6.36 out of 7, mean identification score was 6.34 and mean total score was 6.35. According to CCCRC score: there were no anosmic individuals, 0.5 % were severely hyposmic, 2.6 % were moderately hyposmic,15.3 % were mildly hyposmic and 81.6 % were normosmic. CCCRC olfactory test is cost-effective, simple and practical. It can be easily applied in clinical settings. The CCCRC olfactory test is appropriate for assessment of olfactory function: Turkish population is familiar in terms of the odors used in CCCRC test. The power of this study is that it provides a normative data set against which many factors can be compared.

Anosmia after exposure to a pyrethrin-based insecticide: a case report

We present the case of a subject developing anosmia, preceded by nasal transient irritation and short lasting phantosmia and torqosmia, upon re-entrance into a room treated with a pyrethrin-based insecticide. The concentration of the insecticide in the room is unknown, but relatively high levels are predicted basing upon the modality of exposure and by the irritation symptoms in the subject. Despite corticosteroids therapy, anosmia has persisted unmodified for more than three years; according to, and based on evidence in the literature on olfactory disturbance prognosis, anosmia in this patient is likely to be permanent. The significance of this case report is related to the current wide use of insecticides containing pyrethrin and pyrethroids and highlights the need for more adequate attention to lowering airborne concentrations of pyrethrins and pyrethroids prior to re-entering the treated rooms. In particular, in a closed space sprayed with pyrethrins and pyrethroids insecticide, any irritant symptoms and/or dysosmia should be immediately considered relevant warning signs, and must be avoided.

A Novel Test to Differentiate Anosmic Malingerers from Actually Anosmic Patients

Background

The available olfactory evaluation tests are mainly subjective methods requiring patients’ collaboration. If, for any reason, the patients refuse to honestly report what they perceive, the test reliability will be questionable; this condition is potentially observable in malingering patients because of their financial or psychosocial incentives. In an olfactory discrimination test context, this study was aimed to design a test capable of distinguishing malingerer from actually anosmic or severely hyposmic patients.

Methods

The pilot experiment of our methodology study determined five substances (coffee, lemon, rosewater, thyme, and garlic) as qualified odors of a 20-item odor discrimination test and set its normal reference value at 15. Through two simulations, 70 normosmic participants emulated actual anosmia and also malingering. The outcome results were used to measure test reliability factors.

Results

During the malingering simulation, only seven participants were capable of keeping their scores at the test chance level with enough randomness in their sequences of answers while the actual anosmia simulation revealed that 39 had scores at the test chance level. Accordingly, the Tehran University Odor Discrimination Test (TUODT) was measured to have 90% sensitivity, 55.71% specificity, 67.02% positive predictive value, and 84.78%negative predictive value.

Conclusion

The TUODT is a relatively efficient method to identify anosmia malingerers.

Amount of airflow required for olfactory perception in laryngectomees: a prospective interventional study

OBJECTIVES

To determine minimum airflow rate required for olfactory stimulation in successfully rehabilitated laryngectomised patients after learning the polite yawning technique (PYT) and to confirm the hypothesis that sense of smell is rehabilitated once the nasal airflow is re-established.

DESIGN

Prospective open interventional trial.

SETTING

Tertiary academic hospital.

PARTICIPANTS

The study population comprised 100 laryngectomised patients. The control group consisted of 100 non-laryngectomised patients of similar age and sex. Rhinomanometry was used to measure air flow in the right and left nostrils, respectively, while the Smell Diskettes Olfaction test (SDOT) was used to test each individual's sense of smell.

MAIN OUTCOME MEASURES

The primary endpoint was increasing the airflow, while the secondary endpoint was improvement in the Smell Diskettes Olfaction test score after learning the polite yawning technique.

RESULTS

The difference in the Smell Diskettes Olfaction test results before and after introducing the polite yawning technique was statistically significant (F = 53.077; P < 0.001). The number of accurately identified odours increased with each measurement. There was a significant difference among rhinomanometric measurements of airflow through the right (F = 65.002; P < 0.001) and left nostrils (F = 75.465; P < 0.001). Nasal airflow improved with each measurement. The minimum airflow required for olfactory stimulation in successfully rehabilitated patients was approximately 60 cm(3) /s. The control group had considerably better airflow in both nostrils than the laryngectomised group. The difference between the total number of rehabilitated (normosmic) patients (48%) in the laringectomised group and normosmic participants (56%) in the control group (z = 1.132; P = 0.129) was not statistically significant.

CONCLUSION

The number of odours identified by laryngectomised patients increased with the volume of nasal airflow. The number of patients with rehabilitated olfactory function approximated the percentage of normosmic individuals in the non-laryngectomised population. These findings confirm the hypothesis that sense of smell is rehabilitated once the nasal airflow is re-established.

Olfactory identification testing as a predictor of the development of Alzheimer's dementia: a systematic review

OBJECTIVES/HYPOTHESIS

To evaluate the utility of olfactory identification tests as prognostic instruments for Alzheimer's dementia (AD).

STUDY DESIGN

Systematic review.

METHODS

In accordance with PRISMA guidelines, PubMed and Ovid MEDLINE, EMBASE, ISI Web of Science, PsycINFO, the Cochrane Database of Systematic Reviews, and the Cochrane Central Register of Controlled Trials were searched to determine the quality and quantity of longitudinal and cross-sectional research on this topic.

RESULTS

Two prospective longitudinal cohort studies and 30 cross-sectional studies met inclusion criteria. The prospective longitudinal studies evaluated subjects with or without mild cognitive impairment (MCI) while also using olfactory identification testing as part of a neurocognitive evaluation. The first study reported an increased risk of later onset of AD in subjects with baseline hyposmia, whereas the second study suggested a possible relationship between decreased olfaction in participants with MCI and conversion to AD but was inconclusive due to low follow-up rates. Wide variability in the type of olfactory identification test used and the reporting of results precluded meta-analysis. The cross-sectional studies demonstrated a positive association between poorer performance on olfactory identification testing and AD.

CONCLUSIONS

Although there is evidence suggesting an association between decreased olfaction and AD, rigorously designed longitudinal cohort studies are necessary to clarify the value of olfactory identification testing in predicting the onset of AD.

Odor thresholds and breathing changes of human volunteers as consequences of sulphur dioxide exposure considering individual factors

Objectives

Though sulfur dioxide (SO₂) is used widely at workplaces, itseffects on humans are not known. Thresholds are reported without reference to gender or age and occupational exposure limits are basedon effects on lung functioning,although localized effects in the upper airways can be expected.This study's aim is to determine thresholds with respect to age and gender and suggests a new approach to risk assessment using breathing reflexes presumably triggered by trigeminal receptors in the upper airways.

Methods

Odor thresholds were determined by the ascending method of limits in groups stratified by age and gender.Subjects rated intensities of different olfactory and trigeminal perceptions at different concentrations of SO₂. During the presentation of the concentrations, breathing movements were measured by respiratory inductive plethysmography.

Results

Neither age nor gender effects were observed for odor threshold. Only ratings of nasal irritation were influenced bygender. A benchmark dose analysis on relative respiratory depth revealed a 10%-deviation from baseline at about 25.27 mg/m³.

Conclusion

The proposed new approach to risk assessment appearsto be sustainable. We discuss whether a 10%-deviation of breathingdepth is relevant.

Human olfaction: from genomic variation to phenotypic diversity

The sense of smell is a complex molecular device, encompassing several hundred olfactory receptor proteins (ORs). These receptors, encoded by the largest human gene superfamily, integrate odorant signals into an accurate 'odor image' in the brain. Widespread phenotypic diversity in human olfaction is, in part, attributable to prevalent genetic variation in OR genes, owing to copy number variation, deletion alleles and deleterious single nucleotide polymorphisms. The development of new genomic tools, including next generation sequencing and CNV assays, provides opportunities to characterize the genetic variations of this system. The advent of large-scale functional screens of expressed ORs, combined with genetic association studies, has the potential to link variations in ORs to human chemosensory phenotypes. This promises to provide a genome-wide view of human olfaction, resulting in a deeper understanding of personalized odor coding, with the potential to decipher flavor and fragrance preferences.

Characterizing psychophysical measures of discrimination thresholds and the effects of concentration on discrimination learning in the moth Manduca sexta

What is the spatial and temporal nature of odor representations within primary olfactory networks at the threshold of an animal's ability to discriminate? Although this question is of central importance to olfactory neuroscience, it can only be answered in model systems where neural representations can be measured and discrimination thresholds between odors can be characterized. Here, we establish these thresholds for a panel of odors using a Pavlovian paradigm in the moth Manduca sexta. Moths were differentially conditioned to respond to one odor (CS+) but not another (CS-) using undiluted odorants to minimize salience-dependent learning effects. At 24 and 48 h postconditioning, moths were tested for the presence of a conditioned response (CR) with a blank, then the CS+ and CS- (pseudorandomly) across a 5-log step series of increasing concentration. Results identified discrimination thresholds and established that differential CRs to the CS+ and CS- increased with stimulus concentration. Next, 3 separate groups of moths were differentially conditioned at either one-log step below, at, or one log step above the identified discrimination threshold. At 24 and 48 h postconditioning, moths were tested sequentially with a blank, the concentration used for conditioning, and then undiluted odor. Conditioning at one log step below the discrimination threshold established a CR, indicating both stimulus detection and learning, but was insufficient to establish evidence of discrimination. Moths conditioned at the discrimination threshold were able to discriminate but only when stimulated with undiluted odors, indicating learning, but discrimination measures were hampered. When conditioned above the discrimination threshold, moths had no difficulty in discriminating. These results establish methods for psychophysical characterization of discrimination and indicate that differential conditioning at lowered concentrations biases threshold measures.

Methods for building an olfactometer with known concentration outcomes

We provide detailed instructions and part selections for construction of a five-channel air dilution olfactometer capable of generating neat odorants and binary mixtures at a range of known concentrations. At the heart of the olfactometer is an odorant canister that is (1) cheap and readily available, (2) safe and durable, (3) has minimal odor adherence, (4) is easily incorporated into any olfactometer, and critically (5) produces a highly consistent stimulus. By flowing a given carrier gas at a given flowrate through a given odorant in this canister, the same end-vapor is achieved. Flow/concentration outcomes are provided for several odorants routinely used in olfactometry. This tool will enable researchers to generate known concentrations without expensive analytical machinery.