Olfactory Ability Research Articles

Newly developed method for mouse olfactory behavior tests using an automatic video tracking system

ObjectiveThe mouse is the most popular animal model in olfactory research. Behavior tests with odorants are essential for determining olfactory phenotype. To the best of our knowledge, the mouse olfactory behavior test has not been standardized, making the results vulnerable to inter-observer variation. We sought to develop a new mouse olfactory behavior test assessed by an automatic video tracking system with minimal inter-observer variation. MethodsA video-tracking system was used to automatically track mouse behavior in standard breeding cages with C57BL/6N mice. We tested two odorants (peanut butter for the preference test, 2MB acid for the avoidance test) and distilled water (for a control). Mouse behavior was recorded for 3min and analyzed. For the preference test, investigation time was measured. For the avoidance test, time spent in sectors away from the odorant zone was measured. To confirm our experimental settings, we also evaluated an anosmia mouse model prepared with intranasal administration of ZnSO4. ResultsAll strains of mice showed reproducible behavior patterns of preference or avoidance for the odorants. The anosmia mouse model, as expected, failed to show an olfactory ability for preference or avoidance, and this was well-matched by histologic changes caused by the ZnSO4 treatment. The automatic video tracking system successfully tracked and automatically calculated mouse behavior with good reproducibility. ConclusionOur olfactory behavior test offers a simple and accurate method to evaluate olfactory function in mice. This test can be utilized as a possible standard method to search for features of olfactory phenotypes in mice.

Olfactory function and the social lives of older adults: a matter of sex

Social factors play a critical role in a panoply of health processes, including, as recently demonstrated, olfaction. Here, we investigated sex-dependent differences in the relationship between social lives and ability to identify odors in a large sample of nationally representative older US adults (n = 3005, National Social Life and Aging Project (NSHAP)). Social life was measured by the number of friends and close relatives as well as frequency of socializing. We here confirm the association between social lives and olfactory function and extend the notion by showing specifically that olfactory identification ability is modulated by sex in older adults. The connection between olfactory performance and social lives could reflect social modulation of aging as has been reported for health in general. Future studies are necessary to elucidate the precise mechanisms underlying this association and sex difference.

Awake, long-term intranasal insulin treatment does not affect object memory, odor discrimination, or reversal learning in mice

Intranasal insulin delivery is currently being used in clinical trials to test for improvement in human memory and cognition, and in particular, for lessening memory loss attributed to neurodegenerative diseases. Studies have reported the effects of short-term intranasal insulin treatment on various behaviors, but less have examined long-term effects. The olfactory bulb contains the highest density of insulin receptors in conjunction with the highest level of insulin transport within the brain. Previous research from our laboratory has demonstrated that acute insulin intranasal delivery (IND) enhanced both short- and long-term memory as well as increased two-odor discrimination in a two-choice paradigm. Herein, we investigated the behavioral and physiological effects of chronic insulin IND. Adult, male C57BL6/J mice were intranasally treated with 5μg/μl of insulin twice daily for 30 and 60days. Metabolic assessment indicated no change in body weight, caloric intake, or energy expenditure following chronic insulin IND, but an increase in the frequency of meal bouts selectively in the dark cycle. Unlike acute insulin IND, which has been shown to cause enhanced performance in odor habituation/dishabituation and two-odor discrimination tasks in mice, chronic insulin IND did not enhance olfactometry-based odorant discrimination or olfactory reversal learning. In an object memory recognition task, insulin IND-treated mice did not perform differently than controls, regardless of task duration. Biochemical analyses of the olfactory bulb revealed a modest 1.3 fold increase in IR kinase phosphorylation but no significant increase in Kv1.3 phosphorylation. Substrate phosphorylation of IR kinase downstream effectors (MAPK/ERK and Akt signaling) proved to be highly variable. These data indicate that chronic administration of insulin IND in mice fails to enhance olfactory ability, object memory recognition, or a majority of systems physiology metabolic factors – as reported to elicit a modulatory effect with acute administration. This leads to two alternative interpretations regarding long-term insulin IND in mice: 1) It causes an initial stage of insulin resistance to dampen the behaviors that would normally be modulated under acute insulin IND, but ability to clear a glucose challenge is still retained, or 2) There is a lack of behavioral modulation at high concentration of insulin attributed to the twice daily intervals of hyperinsulinemia caused by insulin IND administration without any insulin resistance, per se.

Effects of olfactory training: a meta-analysis.

The neural plasticity of the olfactory system offers possibilities of treatment in terms of stimulation of the sense of smell, and different studies have suggested effectiveness of smell training, i.e., daily exposition to certain odors. To obtain reliable and precise estimates of overall treatment benefit on the olfactory function, we meta-analyzed the effects of smell training reported in 13 previous studies. We analyzed the smell training effectiveness across three different olfactory abilities, smell identification, discrimination and threshold for odor detection. We found a significant, positive effect of olfactory training for all olfactory abilities, with large effects of training on identification, discrimination and TDI-score and small-to-moderate effect in the case of threshold for odor detection. Interestingly, the pattern of results differed across Sniffin Sticks subtests depending on the origin of participants smell disorder, and the smell training duration influenced its effectiveness in the case of identification and the TDI score. Although the exact mechanism of olfactory recovery following the smell training still requires further investigation, our meta-analysis showed that such training should be considered an addition or alternative to existing smell treatment methods.

Recognition of prey odor in wild meerkats

Although mongooses are well-known to use odor cues in social communication, whether they also use olfaction in foraging is unknown. In this study, I investigated the olfactory ability of wild meerkats to recognize prey items that vary in frequency in their diet. Meerkats aged from 28 days to 2 years were presented with cotton-buds scented with common prey (larvae), less-common prey (scorpions, crickets), non-prey (dung beetles) or a control (no scent). Biting behavior and time spent sniffing the cotton-bud were recorded. Meerkats bit cotton-buds that smelled of larvae more often than cotton-buds that smelled of non-prey or control. They bit cotton-buds that smelled of crickets or scorpions at an intermediate rate. Meerkats’ age and sex did not affect the response. Hence, meerkats can discriminate the odor of their prey from the odor of non-prey items, and tend to show preference for frequent prey over less-common prey. Furthermore, meerkats may use olfactory cues for short-distance detection of prey, but experiments are needed to determine the specific phases of the foraging process where olfaction is involved.

Interaction between age and perceptual similarity in olfactory discrimination learning in F344 rats: relationships with spatial learning

Emerging evidence suggests that aging is associated with a reduced ability to distinguish perceptually similar stimuli in one's environment. As the ability to accurately perceive and encode sensory information is foundational for explicit memory, understanding the neurobiological underpinnings of discrimination impairments that emerge with advancing age could help elucidate the mechanisms of mnemonic decline. To this end, there is a need for preclinical approaches that robustly and reliably model age-associated perceptual discrimination deficits. Taking advantage of rodents' exceptional olfactory abilities, the present study applied rigorous psychophysical techniques to the evaluation of discrimination learning in young and aged F344 rats. Aging did not influence odor detection thresholds or the ability to discriminate between perceptually distinct odorants. In contrast, aged rats were disproportionately impaired relative to young on problems that required discriminations between perceptually similar olfactory stimuli. Importantly, these disproportionate impairments in discrimination learning did not simply reflect a global learning impairment in aged rats, as they performed other types of difficult discriminations on par with young rats. Among aged rats, discrimination deficits were strongly associated with spatial learning deficits. These findings reveal a new, sensitive behavioral approach for elucidating the neural mechanisms of cognitive decline associated with normal aging.

The evidence for olfactory training in treating patients with olfactory loss.

The purpose of this review is to go over the only therapy for olfactory loss supported by level 1a evidence that is currently available, which is olfactory training. This therapy is widely underutilized and has the potential to help many patients with olfactory dysfunction who are otherwise offered no management options. We will review the rationale, clinical studies, and quality of the evidence regarding olfactory training, specifically the olfactory system's inherent ability to regenerate, the plasticity of the system, and the multiple protocols and modifications of protocols present in the literature. Olfactory training is an effective therapy for some patients suffering from olfactory loss, and, while we do not yet know the optimal duration or number of odorants or exact patient population it may be most beneficial for, as an extremely easy, self-driven therapy with no significant side-effects, it should be consistently offered to this patient population.

Seed Detection and Discrimination by Ground Beetles (Coleoptera: Carabidae) Are Associated with Olfactory Cues.

Olfactory ability is an element of fitness in many animals, guiding choices among alternatives such as mating partners or food. Ground beetles (Coleoptera; Carabidae), exhibit preferences for prey, and some species are well-known weed seed predators. We used olfactometer-based bioassays to determine if olfactory stimuli are associated with detection of Brassica napus L., Sinapis arvensis L., and Thlaspi arvense L. seeds by ground beetles characteristic of agroecosystems, and whether behavioural responses to seed odors depended on seed physiological state (imbibed or unimbibed). Imbibed B.napus seeds were preferred over other weed species by two of the three carabid species tested. Only A. littoralis responded significantly to unimbibed seeds of B. napus. Sensitivity to olfactory cues appeared to be highly specific as all carabid species discriminated between the olfactory cues of imbibed brassicaceous weed seeds, but did not discriminate between weed seeds that were unimbibed. Overall, our data suggest that depending on seed physiological state, odours can play an important role in the ability of carabids to find and recognize seeds of particular weed species.

What Makes a Better Smeller?

Olfaction is often viewed as difficult, yet the empirical evidence suggests a different picture. A closer look shows people around the world differ in their ability to detect, discriminate, and name odors. This gives rise to the question of what influences our ability to smell. Instead of focusing on olfactory deficiencies, this review presents a positive perspective by focusing on factors that make someone a better smeller. We consider three driving forces in improving olfactory ability: one's biological makeup, one's experience, and the environment. For each factor, we consider aspects proposed to improve odor perception and critically examine the evidence; as well as introducing lesser discussed areas. In terms of biology, there are cases of neurodiversity, such as olfactory synesthesia, that serve to enhance olfactory ability. Our lifetime experience, be it typical development or unique training experience, can also modify the trajectory of olfaction. Finally, our odor environment, in terms of ambient odor or culinary traditions, can influence odor perception too. Rather than highlighting the weaknesses of olfaction, we emphasize routes to harnessing our olfactory potential.

Making the Most of Mealtimes (M3): protocol of a multi-centre cross-sectional study of food intake and its determinants in older adults living in long term care homes

BackgroundOlder adults living in long term care (LTC) homes are nutritionally vulnerable, often consuming insufficient energy, macro- and micronutrients to sustain their health and function. Multiple factors are proposed to influence food intake, yet our understanding of these diverse factors and their interactions are limited. The purpose of this paper is to fully describe the protocol used to examine determinants of food and fluid intake among older adults participating in the Making the Most of Mealtimes (M3) study.MethodsA conceptual framework that considers multi-level influences on mealtime experience, meal quality and meal access was used to design this multi-site cross-sectional study. Data were collected from 639 participants residing in 32 LTC homes in four Canadian provinces by trained researchers. Food intake was assessed with three-days of weighed food intake (main plate items), as well as estimations of side dishes, beverages and snacks and compared to the Dietary Reference Intake. Resident-level measures included: nutritional status, nutritional risk; disease conditions, medication, and diet prescriptions; oral health exam, signs of swallowing difficulty and olfactory ability; observed eating behaviours, type and number of staff assisting with eating; and food and foodservice satisfaction. Function, cognition, depression and pain were assessed using interRAI LTCF with selected items completed by researchers with care staff. Care staff completed a standardized person-directed care questionnaire. Researchers assessed dining rooms for physical and psychosocial aspects that could influence food intake. Management from each site completed a questionnaire that described the home, menu development, food production, out-sourcing of food, staffing levels, and staff training. Hierarchical regression models, accounting for clustering within province, home and dining room will be used to determine factors independently associated with energy and protein intake, as proxies for intake. Proportions of residents at risk of inadequate diets will also be determined.DiscussionThis rigorous and comprehensive data collection in a large and diverse sample will provide, for the first time, the opportunity to consider important modifiable factors associated with poor food intake of residents in LTC. Identification of factors that are independently associated with food intake will help to develop effective interventions that support food intake.Trial RegistrationClinicalTrials.gov ID: NCT02800291, retrospectively registered June 7, 2016.

Chemical complexity of odors increases reliability of olfactory threshold testing

Assessment of odor thresholds is a widely recognized method of measuring olfactory abilities in humans. To date no attempts have been made to assess whether chemical complexity of odors used can produce more reliable results. To this end, we performed two studies of repeated measures design with 121 healthy volunteers (age 19–62 years). In Study 1, we compared thresholds obtained from tests based on one odor presented in a pen-like odor dispensing device with three odors and six odors mixtures presented in glass containers. In study 2 we compared stimuli of one and three odors, both presented in glass containers. In both studies measurements were performed twice, separated by at least three days. Results indicate that the multiple odor mixtures produced more reliable threshold scores, as compared to thresholds based on a single substance.

Odor Familiarity and Identification Abilities in Adolescents.

Olfactory identification abilities in adolescents have been reported inferior compared with adults. Though this seems to be the case when comparing identification abilities using tests validated on-and for-adults, odor familiarity has been hypothesized to affect identification abilities in younger participants. However, this has never been thoroughly tested. The aims of this study were to investigate patterns in odor familiarity differences between adolescents and adults, and to investigate if an adolescent familiarity-based modification of an identification test could lead to similar identification scores in adolescents and adults. In total, 411 adolescent participants and 320 adult participants were included in the study. Odor familiarity ratings were obtained for 125 odors. A modified version of the "Sniffin' Sticks" identification test was created and validated on 72 adolescents based on adolescent familiarity scores. This test was applied to 82 normosmic adults and 167 normosmic adolescents. Results show a lower familiarity for spices and environmental odors, and a higher familiarity for candy odors in adolescents. The identification abilities in adults and adolescents were equal after familiarity-based modification. We conclude that changes in odor familiarity from adolescence to adulthood do not develop evenly for all odors, but are dependent on odor-object category.

Olfactory Functions in Adults With Autism Spectrum Disorders.

Autism spectrum disorders (ASD) are often characterized by atypical sensory behavior (hyper- or hyporeactivity) although evidence is scarce regarding olfactory abilities in ASD; 16 adults with high-functioning ASD (mean age: 38.2, SD: 9.7) and 14 healthy control subjects (mean age: 42.0 years, SD: 12.5) were assessed in odor threshold, free and cued odor identification, and perceived pleasantness, intensity, and edibility of everyday odors. Although results showed no differences between groups, the Bayes Factors (close to 1) suggested that the evidence for no group differences on the threshold and identification tests was inconclusive. In contrast, there was some evidence for no group differences on perceived edibility (BF01 = 2.69) and perceived intensity (BF01 = 2.80). These results do not provide conclusive evidence for or against differences between ASD and healthy controls on olfactory abilities. However, they suggest that there are no apparent group differences in subjective ratings of odors.

Overlapping Risky Decision-Making and Olfactory Processing Ability in HIV-Infected Individuals.

Given neuroimaging evidences of overlap in the circuitries for decision-making and olfactory processing, we examined the hypothesis that impairment in psychophysical tasks of olfaction would independently predict poor performances on Iowa Gambling Task (IGT), a laboratory task that closely mimics real-life decision-making, in a US cohort of HIV-infected (HIV+) individuals. IGT and psychophysical tasks of olfaction were administered to a Washington DC-based cohort of largely African American HIV+ subjects (N=100), and to a small number of demographically-matched non-HIV healthy controls (N=43) from a different study. Constructs of olfactory ability and decision-making were examined through confirmatory factor analysis (CFA). Structural equation models (SEMs) were used to evaluate the validity of the path relationship between these two constructs. The 100 HIV+ participants (56% female; 96% African Americans; median age = 48 years) had median CD4 count of 576 cells/μl and median HIV RNA viral load <48 copies per milliliter. Majority of HIV+ participants performed randomly throughout the course of IGT tasks, and failed to demonstrate a learning curve. Confirmatory factor analysis provided support for a unidimensional factor underlying poor performances on IGT. Nomological validity for correlations between olfactory ability and IGT performance was confirmed through SEM. Finally, factor scores of olfactory ability and IGT performance strongly predicted 6 months history of drug use, while olfaction additionally predicted hallucinogen use. This study suggests that combination of simple, office-based tasks of olfaction and decision-making may identify those HIV+ individuals who are more prone to risky decision-making. This finding may have significant clinical, public health value if joint impairments in olfaction and IGT task correlates with more decreased activity in brain regions relevant to decision-making.

On the nose: Olfactory disturbances in patients with transient epileptic amnesia.

While olfactory hallucinations are relatively rare in epilepsy, a high prevalence (up to 42%) has been reported in one form - Transient Epileptic Amnesia (TEA). TEA is characterized by recurring amnestic seizures and is commonly associated with persistent interictal memory deficits. Despite reports of changes in smell, olfactory ability has not been objectively assessed in this group. The aim of this study was to measure olfactory ability in patients with TEA and explore whether olfactory symptoms relate to other clinical variables. Fifty-five participants with TEA were recruited from The Impairment of Memory in Epilepsy project database. The presence of olfactory symptoms was obtained via case notes and clinical interview. Participants completed questionnaires to evaluate their olfaction and memory function subjectively. Olfactory ability was measured using the University of Pennsylvania Smell Identification Test (UPSIT). TEA participants' performance was compared to 50 matched healthy control participants. A subset of TEA participants (n=26) also completed a battery of memory tests including standard neuropsychological measures, and assessment of accelerated long-term forgetting and autobiographical memory. Olfactory hallucinations were reported in 55% of patients with TEA. A significant reduction in smell identification (UPSIT) was found between patients with TEA and healthy controls (p<0.001). Epilepsy variables, including history of olfactory hallucinations, were not predictive of olfactory ability. Patients reported ongoing memory difficulties and performed below normative values on objective tests. While no correlation was found between objective measures of memory and olfactory performance, subjective complaints of route finding difficulty was associated with UPSIT score. Impairments in odor identification are common in patients with TEA and exceed changes that occur in normal aging. Olfactory hallucinations occurs in approximately half of patients with TEA, but do not always coincide with reduced sense of smell. Olfactory impairment and interictal memory problems both occur frequently in TEA but are not closely associated.

The smell of terroir! Olfactory discrimination between wines of different grape variety and different terroir

The French term ‘terroir’ refers to the relationship between a particular wine and the specific place where it is produced. To date, no investigation has directly tested in an experimentally-controlled setting whether participants can detect different terroirs in wines, and if their level of expertise can modulate such performance. We investigated wine olfactory discrimination ability by using a computer-controlled olfactometer. Participants’ ability to discriminate two wines only based on the olfactory features of their terroir (zone and vineyard), their variety (e.g., cabernet vs. merlot) or both was tested. Olfactory discrimination performance of both novices and wine-professionals reflected whether two wines differed by terroir, variety or both. Performance peaked when wines differed in both terroir and variety, with terroir being more easily discriminated than variety. These results, obtained by controlling for the first time the precision of the olfactory stimulation, provide insightful clues in understanding the wine appreciation process, specifically with respect to the perceptual aspects of terroir.

Assessment of Olfactory Memory in Olfactory Dysfunction.

To assess all clinically relevant components of olfactory perception, examinations for olfactory sensitivity, discrimination, and identification are performed. Besides the standard perceptual test battery, episodic olfactory memory might offer additional information about olfactory abilities relative to these standard clinical tests. As both olfactory deficits and memory deficits are early symptoms in neurodegenerative disorders, olfactory memory may be of particular interest. However, to date little is known about episodic olfactory memory performance in patients with decreased olfactory function. This study includes the investigation of olfactory memory performance in 14 hyposmic patients (8 female, mean age 52.6 years) completing two episodic odor memory tests (Sniffin' Test of Odor Memory and Odor Memory Test). To control for a general impairment in memory function, a verbal and a figural memory test were carried out. A regression model with multiple predictors was calculated for both odor memory tests separately. Odor identification was identified as the only significant predictor for both odor memory tasks. From our results, we conclude that currently available olfactory memory tests are highly influenced by odor identification abilities, implying the need for the development and validation of additional tests in this field which could serve as additional olfactory perception variables for clinical assessment.

Neonicotinoid-induced impairment of odour coding in the honeybee.

Exposure to neonicotinoid pesticides is considered one of the possible causes of honeybee (Apis mellifera) population decline. At sublethal doses, these chemicals have been shown to negatively affect a number of behaviours, including performance of olfactory learning and memory, due to their interference with acetylcholine signalling in the mushroom bodies. Here we provide evidence that neonicotinoids can affect odour coding upstream of the mushroom bodies, in the first odour processing centres of the honeybee brain, i.e. the antennal lobes (ALs). In particular, we investigated the effects of imidacloprid, the most common neonicotinoid, in the AL glomeruli via in vivo two-photon calcium imaging combined with pulsed odour stimulation. Following acute imidacloprid treatment, odour-evoked calcium response amplitude in single glomeruli decreases, and at the network level the representations of different odours are no longer separated. This demonstrates that, under neonicotinoid influence, olfactory information might reach the mushroom bodies in a form that is already incorrect. Thus, some of the impairments in olfactory learning and memory caused by neonicotinoids could, in fact, arise from the disruption in odor coding and olfactory discrimination ability of the honey bees.

Olfactory ability in normal pressure hydrocephalus as compared to Alzheimer's disease and healthy controls

ObjectivesNormal pressure hydrocephalus (NPH) is a treatable neurological disorder that appears in older adults, lacks specific diagnostic criteria, and resembles symptoms seen in Alzheimer's disease (AD). Presently, differentiating NPH from AD in the early stages of symptom presentation remains difficult. This study established whether olfactory testing may be useful in this regard. In addition, we determined whether olfactory function of NPH patients differed before and after extended lumbar drainage (ELD), as well as six months after surgical implantation of a ventriculoperitoneal (VP) shunt. Patients and methodsTwenty-two NPH patients (mean age=77.6yrs), 14 age- and gender-matched healthy controls (mean age=79.9yrs), and 7 AD patients (mean age=75.5yrs) were administered the 40-item University of Pennsylvania Smell Identification Test (UPSIT). Eighteen of the 22 NPH patients were also tested following ELD and 8 patients were tested six months following implantation of VP shunt. ResultsPrior to ELD, patients with NPH scored significantly higher on the UPSIT than those with AD [respective means (SDs)=26.9 (7.1) & 14.1 (4.7)]. While the mean NPH score was significantly below that of the matched controls [control mean (SD)=32.7 (6.7)], their test scores were nonetheless within the general normal range, as determined from published normative data (48th percentile). The UPSIT scores did not differ significantly among the three longitudinal time points in the NPH patients. ConclusionOlfactory testing may be useful in differentiating between patients with NPH and patients with AD. Odor identification test scores of NPH patients are not influenced by the release of intracranial pressure via ELD or six months following implantation of a VP shunt.

The genetics of canine olfaction

Dogs have a great sense of olfaction, but unlike many other mammals, which also show superior olfactory performance, many dog breeds have been created for hunting purposes for which olfactory performance is particularly important. In this article, we review the dog genetic characteristics that could make dogs so gifted with respect to olfactory ability. We also present some preliminary results on RNA profiling analyses of dog olfactory epithelium and show that the level of olfactory receptor expression per olfactory neuron might be higher in dogs than in rats.