General Olfactory Function Research Articles

The efficacy of olfactory training in improving olfactory function: a meta-analysis

PurposeStudy the efficacy of olfactory training in smell recovery.MethodsAn extensive search was performed through different databases in order to find articles analyzing the efficacy of olfactory training as a treatment for olfactory dysfunction. Methodological quality of primary studies within the final sample was assessed following PRISMA guidelines. Standardized mean differences in pre–post olfactory training groups, and also in experimental-control and pre-follow up if possible, were computed by Hedges’ g effect size statistic. Each effect size was weighted by its inverse variance.ResultsFinal sample was composed of 36 articles (45 pre–post effect sizes). Contrasts were performed separately for odor identification, odor discrimination, odor threshold and general olfactory function. Moderate to large and heterogeneous effect was obtained for olfactory function (g = 0.755, k = 45, SE = 0.093, CI 95% = [0.572, 0.937]), different moderators had a significant effects, such as, training duration, age and anosmia diagnosis.ConclusionOlfactory training was found to have a positive and significant effect on rehabilitating the olfactory function.

Androstadienone sensitivity is associated with attention to emotions, social interactions, and sexual behavior in older U.S. adults.

Δ 4,16-androstadien-3-one (androstadienone) is a putative human pheromone often linked to sexual attraction in young adults, although specific associations with sexual behavior are not yet established. Androstadienone also serves a broader social-emotional function beyond the sexual domain, specifically tuning the brain to efficiently process emotional information. Whether these effects persist throughout the lifespan into post-reproductive life is unknown. In a laboratory study of older adults, those with greater androstadienone odor sensitivity paid greater attention to subliminal emotional information, specifically, angry faces (p = 0.05), with a similar relationship to happy faces. In contrast, the physical odor n-butanol (a control) did not affect emotional attention (p = 0.49). We then extended this laboratory research and determined whether sensitivity to androstadienone affects the everyday lives of older adults by measuring their social and sexual behavior. In this second study, we surveyed in a nationally representative sample of US older adults living in their homes (National Social Life and Aging Project, 62-90 years; n = 2,086), along with their sensitivity to androstadienone, general olfactory function, health and demographics. Greater sensitivity to androstadienone was associated with richer social lives: having more friends, increased communication with close friends and family, and more participation in organized social events and volunteer activities (all p's ≤ 0.05, generalized linear models, adjusted for age and gender). It was also associated with more recent sexual activity, more frequent sexual thoughts, and viewing sex as an important part of life (all p's ≤ 0.05). General olfactory function did not explain these associations, supporting a specialized function for this pheromone during everyday life, and expanding its role to social life as well as sexual behavior, likely mediated by enhanced attention to emotional information.

Anosmia Testing as Early Detection of SARS-CoV-2 Positivity; A Prospective Study under Screening Conditions.

Sudden onset of anosmia is a phenomenon often associated with developing COVID-19 disease and has even been described as an initial isolated symptom in individual cases. In this case-control study, we investigated the feasibility of this condition as a suitable screening test in a population at risk. We performed a prospective study with a total of 313 subjects with suspected SARS-CoV-2 infection. In parallel to routine PCR analysis, a modified commercial scent test was performed to objectify the presence of potential anosmia as a predictor of SARS-CoV-2 positivity. Furthermore, a structured interview assessment of the participants was conducted. A total of 12.1% of the study participants had molecular genetic detection of SARS-CoV-2 infection in the nasopharyngeal swab. It could be demonstrated that these subjects had a significantly weaker olfactory identification performance of the scents. Further analysis of the collected data from the scent test and medical history via random forest (Boruta) algorithm showed that no improvement of the prediction power was achieved by this design. The assay investigated in this study may be suitable for screening general olfactory function. For the screening of COVID-19, it seems to be affected by too many external and internal biases and requires too elaborate and selective pre-test screening.

The relationship between individual significance of olfaction and measured olfactory function

• The Threshold-Detection-Identification (TDI) test measures olfactory function. • The Importance of Olfaction Questionnaire (IO-Q) measures subjective importance. • TDI and IO-Q are only weakly correlated. • Olfactory function and subjective importance of olfaction are distinct. The subjective importance of olfaction varies greatly across individuals, yet the cause of this variation – such as its relationship to general olfactory function – remains poorly understood. The purpose of this descriptive correlational study was to examine if any relationship exists between subjectively reported significance of olfactory experience and more objective, psychophysical olfactory testing. Specifically, we related the Importance of Olfaction questionnaire (IO-Q), the threshold-discrimination-identification test (TDI) and both their subscales in Bayesian correlation analyses using R and JASP in a sample of 227 neurotypical, young participants from Denmark. The mean age was 27.71 (∼57% females). 176 participants fully completed all tests. We found that the total IO-Q score was weakly positively correlated to the total TDI score ( r = 0.141, 95% CI = [-0.007;0.281]). The total TDI score was also weakly positively correlated to the aggravation subscale of the IO-Q ( r = 0.117, 95% CI = [0.021; 0.210]), but less so to other subscales. This indicates that greater subjective olfactory importance is only weakly associated with greater measured olfactory function. As such, olfactory test scores may not provide the full picture of olfactory function.

Impact of anterior skull base fracture on lateralized olfactory function.

Data on the impact of anterior skull base fractures (aSBF) on lateralized olfactory function are missing. The goal of the study was to investigate olfactory function in patients with traumatic brain injury (TBI) due to aSBF separately for each side and assess the frequency of lateralized smell impairment. Retrospective, single center study of olfactory function in 93 patients with aSBF. Olfactory function was assessed by means of the Sniffin' Sticks test battery for each side of the nose, separately. TBI severity was graded according to the Glasgow Coma Scale. Average time interval between olfactory test and trauma was 6.5 years. General olfactory function was defined as the best side out of both nostrils. A total of 50 patients had unilateral and 43 patients bilateral aSBF. The grade of TBI was inversely correlated with olfactory function. General olfactory function was significantly worse in patients with bilateral aSBF compared to patients with unilateral aSBF. Clinically significant side by side differences in olfactory function were found in 18 and 30% respectively for unilateral and bilateral aSBF. Grade of TBI had no significant impact on side differences. Among patients with unilateral aSBF olfactory function was not significantly different between the fractured and the non-fractured side. The severity of TBI and bilateral more than unilateral aSBF results in more impaired olfactory function. Lateralized olfactory deficits were not more frequent in any group, regardless of the fracture type and side.

Smell training improves olfactory function and alters brain structure

Training and repeated exposure to odorants leads to enhanced olfactory sensitivity. So far, the efficacy of intensive olfactory training on olfactory function in a healthy population and its underlying neurobiological basis remain poorly known. This study investigated the effects of a 6-week intensive and well-controlled olfactory training on olfactory function and brain structure/neuroplasticity. Thirty-six healthy young individuals were recruited and randomly distributed in three groups: (1) 12 participants underwent daily intensive olfactory training of at least 20 min that included an (a) odor intensity classification task, an (b) odor quality classification task and an (c) target odor detection task, (2) 12 participants underwent an equivalent visual control training, and (3) 12 control individuals did not participate in any training. Before and after the training period, all participants performed a series of olfactory tests and those from groups 1 and 2 underwent structural magnetic resonance (MR) imaging, from which we obtained measures such as cortical thickness and tissue density.Participants improved in the respectively trained tasks throughout the 6-weeks training period. Those who underwent olfactory training improved general olfactory function compared to control participants, especially in odor identification, thus showing intramodal transfer. Further, MR imaging analysis revealed that olfactory training led to increased cortical thickness in the right inferior frontal gyrus, the bilateral fusiform gyrus and the right entorhinal cortex.This research shows that intensive olfactory training can generally improve olfactory function and that this improvement is associated with changes in the structure of olfactory processing areas of the brain.

Mother-child bonding is associated with the maternal perception of the child's body odor

Mothers can recognize the odor of their baby and typically adore this odor. In line with this observation, infant body odors activate reward-related brain areas in the mothers. In some mother-child-dyads however, the mutual bond is impaired and mothers have trouble engaging in interaction with their child. We aimed to examine how mothers with bonding difficulties perceive their child's body odor.In total, 75 mothers of babies aged 0–12 months were examined: Twenty-five of those were recruited in a psychosomatic day hospital ward, which is specialized for mother-child bonding disorders. Fifty age-matched healthy women and their babies served as controls. Body odor samples of each baby were collected from bodysuits in a highly standardized procedure. Thereafter, each mother rated the samples of her own and two other infants in a blind and randomized design. In addition, general olfactory function in terms of threshold and identification ability was tested and the mother reported the bonding to her baby in a standardized questionnaire.Healthy mothers showed a clear preference of their own compared to odors of other infant's, while mothers with bonding difficulties did not. Furthermore, the degree of preference was negatively correlated to self-reported bonding difficulties. Mothers with bonding difficulties could not identify their own infant's odor above chance, while control mothers could. Both groups did not differ in general olfactory function.We assume that reduced close body contact and interaction time associated with bonding difficulties may lead to reduced exposure and hinder the recognition of the infantile body odor. Within a vicious cycle, a reduced hedonic experience smelling their own baby may prevent women from deliberately approaching the baby. Thus, the positive and bond-building consequences of bodily and sensory interaction cannot unfold. As the baby's odor is normally perceived as very pleasant and rewarding, the conscious perception of the infantile body odor may be an additive therapeutic approach for mothers with bonding difficulties.

Paradoxical olfactory function in combat Veterans: The role of PTSD and odor factors

ABSTRACTStress- and trauma-related disorders, including posttraumatic stress disorder (PTSD), are characterized by an increased sensitivity to threat cues. Given that threat detection is a critical function of olfaction and that combat trauma is commonly associated with burning odors, we sought a better understanding of general olfactory function as well as response to specific trauma-related (i.e. burning) odors in combat-related PTSD. Trauma-exposed combat Veterans with (n = 22) and without (n = 25) PTSD were assessed for general and specific odor sensitivities using a variety of tools. Both groups had similar general odor detection thresholds. However, the combat Veterans with PTSD, compared to combat Veterans with comparable trauma exposure but without PTSD, had increased ratings of odor intensity, negative valence, and odor-triggered PTSD symptoms, along with a blunted heart rate in response to burning rubber odor. These findings are discussed within the context of healthy versus pathological changes in olfactory processing that occur over time after psychological trauma.

Olfactory training with older people.

Loss of olfactory function is largely found with aging. Such a reduction in olfactory function affects quality of life and enhances likelihood of depressive symptoms. Furthermore, it has been shown that reduction in olfactory function is associated with cognitive impairment and several diseases such as major depression. Because several studies suggest that discontinuous exposure to odors may improve general olfactory function, the primary aim of this study was to investigate whether such "olfactory training" has positive effects on subjective well-being and cognitive function. We performed a controlled, unblinded, longitudinal study SETTING: The study took place at an outpatients' clinic of a Department of Otorhinolaryngology at a Medical University. A total of 91 participants (age 50 to 84years) completed testing. They were randomly assigned to an olfactory training (OT) group (N=60) and a control group (N=31). The study included two appointments at the Smell and Taste Clinic. Olfactory and cognitive function as well as subjective well-being was tested using standardized tests. During the 5-month interval between sessions, the OT group completed daily olfactory exposure. During the same time, the control group completed daily Sudoku problems. Analyses show a significant improvement of olfactory function for participants in the OT group and improved verbal function and subjective well-being. In addition, results indicated a decrease of depressive symptoms. Based on the present results, OT may constitute an inexpensive, simple way to improve quality of life in older people. Copyright © 2017 John Wiley & Sons, Ltd.

Disgust-Related Olfactory Processing: The Role of Gender and Trait Disgust.

For the rejection of disgusting and potentially health-threatening food, the sense of smell plays a critical role. We conducted two experiments in order to investigate the role of gender and trait disgust (the temporally stable tendency to experience disgust across different situations) on disgust-related olfactory processing. A total of 40 men and women (Study 1), as well as a group of women divided according to high versus low trait disgust (Study 2, n = 59), were compared with regard to their odor thresholds for carbon disulfide (which smells like spoiled food) and a control stimulus ( n-butanol). The stimuli were rated for experienced arousal, negative valence, and familiarity. In addition, all participants underwent the "Sniffin' Sticks" battery assessing general olfactory performance. We found that women had a lower carbon disulfide threshold and rated this odorant as more unpleasant than men. Trait disgust was neither associated with the detection of the odorant signaling spoilage, nor with general olfactory function. The latter finding questions the role of this personality trait for olfactory-driven food-rejection responses, at least for normosmic individuals.

Relation of the volume of the olfactory bulb to psychophysical measures of olfactory function.

The aim of this review is to investigate whether changes in olfactory bulb volume relate to changes in specific olfactory functions. We studied currently available peer-reviewed articles on the volume of the human olfactory bulb that also included a psychophysical measure of olfactory function. In the present review, we observed a very clear and consistent correlation between general olfactory function and olfactory bulb (OB) volume. We were not able to find a clear relationship between a specific smell component and OB volume, even when analyzing pathologic conditions separately. In some cases, changes were observed for different subtests, but these changes did not significantly correlate with OB volume or had only a borderline correlation. In other cases, we found contradictory data. Several factors may contribute to the difficulties in finding correlations with the different components of smell: (1) the OB volume may be influenced by information from olfactory receptor neurons (bottom-up effect), information from central nervous system (top-down effect) and by direct damage; (2) most pathologic conditions affect more than one area of the olfactory pathway; (3) small sample sizes of hyposmic subjects were used. We believe that it is necessary to do further studies with larger numbers of subjects to answer the currently investigated question.

Olfactory Training in Patients with Parkinson's Disease

ObjectiveDecrease of olfactory function in Parkinson's disease (PD) is a well-investigated fact. Studies indicate that pharmacological treatment of PD fails to restore olfactory function in PD patients. The aim of this investigation was whether patients with PD would benefit from “training” with odors in terms of an improvement of their general olfactory function. It has been hypothesized that olfactory training should produce both an improved sensitivity towards the odors used in the training process and an overall increase of olfactory function.MethodsWe recruited 70 subjects with PD and olfactory loss into this single-center, prospective, controlled non-blinded study. Thirty-five patients were assigned to the olfactory training group and 35 subjects to the control group (no training). Olfactory training was performed over a period of 12 weeks while patients exposed themselves twice daily to four odors (phenyl ethyl alcohol: rose, eucalyptol: eucalyptus, citronellal: lemon, and eugenol: cloves). Olfactory testing was performed before and after training using the “Sniffin' Sticks” (thresholds for phenyl ethyl alcohol, tests for odor discrimination, and odor identification) in addition to threshold tests for the odors used in the training process.ResultsCompared to baseline, trained PD patients experienced a significant increase in their olfactory function, which was observed for the Sniffin' Sticks test score and for thresholds for the odors used in the training process. Olfactory function was unchanged in PD patients who did not perform olfactory training.ConclusionThe present results indicate that olfactory training may increase olfactory sensitivity in PD patients.

Effects of olfactory training in patients with olfactory loss

Olfactory function is known to be modulated by repeated exposure to odors. The aim of this investigation was whether patients with olfactory loss would benefit from "Training" with odors in terms of an improvement of their general olfactory function. It was hypothesized that olfactory Training should produce both an improved sensitivity towards the odors used in the Training process and an overall increase of olfactory function. The prospective study was performed in patients with olfactory dysfunction. One group of patients performed the Training (n = 40), whereas another part did not (n = 16). Exclusion criteria for patients were sinunasal disease. Olfactory training was performed over a period of 12 weeks. Patients exposed themselves twice daily to four intense odors (phenyl ethyl alcohol: rose, eucalyptol: eucalyptus, citronellal: lemon, and eugenol: cloves). Olfactory testing was performed before and after training using the "Sniffin' Sticks" (thresholds for phenyl ethyl alcohol, tests for odor discrimination and odor identification) in addition to threshold tests for the odors used in the training process. Compared to baseline, training patients experienced an increase in their olfactory function, which was observed for the Sniffin' Sticks test score and for thresholds for the odors used in the training process. In contrast, olfactory function was unchanged in patients who did not perform olfactory training. The present results indicate that the structured, short-term exposure to selected odors may increase olfactory sensitivity.

Androstadienone odor thresholds in adolescents

A sex-related difference in olfactory sensitivity to androstenone has been reported to occur during adolescence. More males than females exhibited anosmia to androstenone, or an increase in androstenone threshold with age. The current study addressed the question whether similar, sexually dimorphic effects of aging over puberty can also be found for androstadienone. A total of 102 subjects participated (36 females, 66 males). Similar to previous investigations, subjects were divided into a group of 47 individuals with a mean age of 13.3 years, defined as pre/peri-pubertal, and a group of 55 subjects with a mean age of 17.1 years, defined as post-pubertal. All subjects underwent tests for verbal abilities, general olfactory function, and measurements of androstadienone thresholds. The study provided the following major results: (1) Male subjects exhibited higher androstadienone sensitivity in the pre/peri-pubertal group as compared to the post-pubertal group. This difference was not observed in female subjects. Correspondingly, a negative correlation between age and androstadienone sensitivity was found for male subjects, but not for female subjects. (2) In contrast to this sex-specific change of the androstadienone odor threshold, verbal skills and odor identification abilities increased with age in all subjects regardless of their sex. In conclusion, the present observations confirm previous research on sex-differentiated effects of aging during puberty on sensitivity towards odorous steroids. While the underlying causes are unknown, it may be hypothesized that the decreased sensitivity could result from the increased endogenous levels of androstadienone in male subjects. Future studies should include both steroid and non-steroid odorants to futher explore these age-related changes.

Olfactory Sensitivity of Subjects Working in Odorous Environments

The aim of the present study was to investigate whether people with a professional interest in odors also exhibit higher olfactory sensitivity. To this end, we investigated 58 subjects (age 33.6 +/- 11.0 years, mean +/- SD; 55 women) employed in perfume retail outlets and compared their olfactory sensitivity to 58 controls (age 34.6 +/- 9.9 years; 53 women) matched for age, gender and professional activities who did not work in such odorous environments. Olfactory function was assessed using the 'Sniffin' Sticks' test kit which includes tests for n-butanol odor threshold, odor discrimination and odor identification. Subjects working in perfume retail outlets scored higher in odor discrimination tests compared to controls. Working in an odorous environment for a full day had no major effect on general olfactory abilities, as indicated by measures performed at the beginning and end of a working day. Taken together, results from the present study do not support the idea that odorous environments are deleterious to general olfactory function.

Sex pheromone systems in goldfish: comparisons to vomeronasal systems in tetrapods.

Most amphibians, reptiles and mammals possess a well defined dual olfactory system comprised of separate neural pathways that regulate different olfactory functions. One pathway originates in the nasal cavity and gives rise to what is commonly referred to as the main olfactory system. The other pathway originates in the vomeronasal organ (VNO) and gives rise to the accessory olfactory system. Functionally, the main olfactory system is thought to subserve, olfactory-mediated tasks such as feeding and grooming, while the accessory olfactory system is believed to be primarily involved in mediating behavioral and physiological responses to sex pheromones. Traditionally, it has been difficult to address whether teleosts possess any components of the vomeronasal system, since they generally do not meet the criteria used to identify vomeronasal systems in other vertebrates. Previous conclusions that the nasal epithelia of fish is olfactory and not vomeronasal in nature are based on observations that teleosts lack a separate VNO-like chemosensory structure and an anatomically distinct accessory olfactory bulb. However, because sex pheromones have been identified in the goldfish, it is now possible to compare the neural substrates that regulate pheromone-induced responses in teleosts to those that mediate similar responses in other vertebrates. The olfactory system in goldfish is particularly well suited for such comparisons, because it comprises anatomical and functional subdivisions that resemble those associated with the main and accessory olfactory systems in tetrapods. The olfactory pathways that mediate endocrine and behavioral responses to sex pheromones in goldfish are described and then compared to the main and accessory olfactory systems of tetrapods. In making these comparisons, a number of similarities become apparent. First, the olfactory pathways that regulate responses to sex pheromones in goldfish are different from those that serve a more general olfactory function. Second, these functional differences appear to be subserved by separate and anatomically distinct olfactory tract projections to the brain. Third, the lateral olfactory tracts and their central projections in goldfish appear to serve a function analogous to that of the main olfactory system, while the medial olfactory tracts and their central projections comprise a pathway remarkably similar to the vomeronasal-accessory olfactory system. These findings suggest that teleosts may possess functional correlates of tetrapod vomeronasal systems, but in a form that has yet to be recognized. If so, medial olfactory tract projections in goldfish may be evolutionarily conserved and expressed in tetrapods as the vomeronasal system, or the medial olfactory tract projections may be new pathways that have evolved to serve the same function.

Sex Pheromone Systems in Goldfish: Comparisons to Vomeronasal Systems in Tetrapods (Part 2 of 2)

Most amphibians, reptiles and mammals possess a well defined dual olfactory system comprised of separate neural pathways that regulate different olfactory functions. One pathway originates in the nasal cavity and gives rise to what is commonly referred to as the main olfactory system. The other pathway originates in the vomeronasal organ (VNO) and gives rise to the accessory olfactory system. Functionally, the main olfactory system is thought to subserve olfactory-mediated tasks such as feeding and grooming, while the accessory olfactory system is believed to be primarily involved in mediating behavioral and physiological responses to sex pheromones. Traditionally, it has been difficult to address whether teleosts possess any components of the vomeronasal system, since they generally do not meet the criteria used to identify vomeronasal systems in other vertebrates. Previous conclusions that the nasal epithelia of fish is olfactory and not vomeronasal in nature are based on observations that teleosts lack a separate VNO-like chemosensory structure and an anatomically distinct accessory olfactory bulb. However, because sex pheromones have been identified in the goldfish, it is now possible to compare the neural substrates that regulate pheromone-induced responses in teleosts to those that mediate similar responses in other vertebrates. The olfactory system in goldfish is particularly well suited for such comparisons, because it comprises anatomical and functional subdivisions that resemble those associated with the main and accessory olfactory systems in tetrapods. The olfactory pathways that mediate endocrine and behavioral responses to sex pheromones in goldfish are described and then compared to the main and accessory olfactory systems of tetrapods. In making these comparisons, a number of similarities become apparent. First, the olfactory pathways that regulate responses to sex pheromones in goldfish are different from those that serve a more general olfactory function. Second, these functional differences appear to be subserved by separate and anatomically distinct olfactory tract projections to the brain. Third, the lateral olfactory tracts and their central projections in goldfish appear to serve a function analogous to that of the main olfactory system, while the medial olfactory tracts and their central projections comprise a pathway remarkably similar to the vomeronasal-accessory olfactory system. These findings suggest that teleosts may possess functional correlates of tetrapod vomeronasal systems, but in a form that has yet to be recognized. If so, medial olfactory tract projections in goldfish may be evolutionarily conserved and expressed in tetrapods as the vomeronasal system, or the medial olfactory tract projections may be new pathways that have evolved to serve the same function.

Clinical application of the smell identification test

Clinical application of the standardized "scratch and sniff" olfactory test in Japanese is described. Over 300 subjects participated in three experiments. In experiment 1, 29 odorants used in the smell identification test were rated as to their experiences. The ratios of the experiences in each combination of odorants were compared. In experiment 2, the test was applied to normal subjects. Average test scores decreased as a function of age, with the greatest decline occurring between the sixth and tenth decades of life. In experiment 3, the test was shown to differentiate between subjects with olfactory disorders and normal controls. This self-administered test now makes it possible to rapidly and accurately assess general olfactory function in the laboratory, clinic, or through the mail without complex equipment or space consuming stores of chemicals.

Development of the university of pennsylvania smell identification test: A standardized microencapsulated test of olfactory function

The development of the first standardized “scratch'n sniff” olfactory test is described. Over 1600 subjects participated in five experiments. In Experiment 1, 50 microencapsulated odorants were rated as to their intensity, pleasantness, irritation, coolness, and familiarity, and two procedures for releasing them were compared. In Experiment 2, the results of the first experiment and familiarity, and two procedures for releasing them were compared. In Experiment 2, the results of the first experiment and other data were used in the development of the test, which was administered to a large number of subjects. Using multiple regression analysis, scores on this test were shown to be significantly related to the subjects' gender, ethnic background, and smoking behavior. Average test scores decreased as a function of age, with the greatest decline occurring between the sixth and tenth decades of life. These age-related changes were not correlated with scores on the Wechsler Memory Scale. Women performed better than men within all age categories. In Experiment 3, the test was shown to differentiate between subjects with known olfactory disorders (e.g., Kallmann's syndrome; Korsakoff s syndrome) and normal controls, and to reliably detect persons instructed to feign total anosmia. In Experiment 4, the test-retest reliability was established (6-month interval; r=0.918, p<0.001), and in Experiment 5 the test was shown to correlate thresholds with odor detection (r=−0.794, p<0.001). This self-administratered test now makes it possible to rapidly and accurately assess general olfactory function in the laboratory, clinic, or through the mail without complex equipment or space-consuming stores of chemicals.