Life-span development of odor identification, learning, and olfactory sensitivity

Distinct Age-Specific Effects on Olfactory Associative Learning in C57BL/6 Substrains

C57BL/6 is the most widely used mouse strain in the laboratories. Two substrains of C57BL/6, C57BL/6J (B6J), and C57BL/6N (B6N) are well-known backgrounds for genetic modification and have been shown difference in quite a few tests, including open field test, rotarod test, and Morris water maze. However, difference between these two substrains in olfaction-dependent behaviors remains unknown. Here, we used olfactory two-alternative choice task, which is modified to have two training stages, to evaluate animals’ ability in instrumental learning and olfactory association. In the first (rule learning) stage, the mice were trained to use the operant chamber to collect water rewards. An odor cue was provided in the procedure, with no indication about reward locations. In the following (discrimination learning) stage, two odor cues were provided, with each indicating a specific water port. The animals were rewarded upon correct port choices following cue deliveries. We found that during young adulthood (7–10 weeks old), proportionally more B6J than B6N mice were able to pass rule learning (58.3% vs. 29.2%) and ultimately acquire this task (54.2% vs. 25%), with the two substrains showing similar pass rates in discrimination learning (92.9% vs. 85.7%). Surprisingly, at a more mature age (17 weeks old), this substrain difference disappeared. Mature B6N mice had a significant improvement in pass percentages of rule learning and overall task, whereas similar improvement was not observed in the B6J counterparts. Instead, mature B6J mice had an improved speed in rule learning and overall task. We further examined behavioral patterns of 8-week-old B6J and B6N mice in the olfactory habituation or dishabituation test. We observed normal olfactory habituation from subjects of both substrains, with the B6J mice exhibiting stronger investigative responses to newly presented odorants. These results reveal for the first time that B6J and B6N mice are different in acquisition processes of a behavioral task that requires instrumental learning and olfactory association, and that maturation appears to employ different effects on these two substrains during these processes. Furthermore, young adult B6J and B6N mice might be similar in olfactory habituation but different in the olfactory aspects of novelty seeking.

Crossmodal Associations with Olfactory, Auditory, and Tactile Stimuli in Children and Adults

People associate information with different senses but the mechanism by which this happens is unclear. Such associations are thought to arise from innate structural associations in the brain, statistical associations in the environment, via shared affective content, or through language. A developmental perspective on crossmodal associations can help determine which explanations are more likely for specific associations. Certain associations with pitch (e.g., pitch-height) have been observed early in infancy, but others may only occur late into childhood (e.g., pitch-size). In contrast, tactile-chroma associations have been observed in children, but not adults. One modality that has received little attention developmentally is olfaction. In the present investigation, we explored crossmodal associations from sound, tactile stimuli, and odor to a range of stimuli by testing a broad range of participants. Across the three modalities, we found little evidence for crossmodal associations in young children. This suggests an account based on innate structures is unlikely. Instead, the number and strength of associations increased over the lifespan. This suggests that experience plays a crucial role in crossmodal associations from sound, touch, and smell to other senses.

Odor identification performance in children aged 3-6 years

BACKGROUND

While valid and reliable olfactory tests have been developed for children aged >5 years, olfactory testing has not systematically been evaluated in younger children. The aim of this study was to evaluate the reliability and validity of the "U-Sniff" odor identification test in children aged 3-6 years.

METHODS

We included 160 healthy children (age range 3-6 years) and 14 congenitally anosmic children. Participants were investigated in two identical sessions. The "U-Sniff" test was used to evaluate olfactory function. A picture identification test (PIT) and the Kasel-Concentration-Task (KKA) were administered to identify factors influencing odor identification performance.

RESULTS

Age significantly influenced odor identification performance, with older children achieving higher scores. PIT and KKA scores correlated positively with odor identification scores. The "U-Sniff" test demonstrated a high test-retest reliability (r₁₆₀ = 0.75, p < 0.001). It was possible to distinguish between healthy and anosmic children by means of "U-Sniff" scores starting at age 4 years with high sensitivity (79-93%) and specificity (88-95%).

CONCLUSIONS

The "U-Sniff" test is feasible for children starting at age 3 years. In children aged ≥4 years, it is a reliable and valid method to distinguish between normal olfactory function and anosmia.

IMPACT

Olfactory testing is reliable and valid starting at an age of 4 years. The study adds a systematic evaluation of olfactory testing in young children. Results of this study are especially interesting for clinicians in the diagnosis of olfactory dysfunction.

The Influence of Cognitive Parameters on Olfactory Assessment in Healthy Children and Adolescents

Olfactory threshold and odor identification tests are frequently used for assessment of olfactory function in children and adolescents. Whether olfactory test results are influenced by cognitive parameters or sex in children and adolescents is largely unknown. The aim of this study was to investigate the influence of cognition, age and sex on "Sniffin' Sticks" olfactory threshold and "U-Sniff" odor identification performance in a pediatric population. A total of 200 participants between age 6 and 17 years were included. Olfactory function (olfactory threshold and odor identification) was assessed using the "Sniffin' Sticks." In addition, age appropriate cognitive testing was applied. The results of this study indicate that odor identification test performance is positively correlated with age (r = 0.31) and verbal abilities of children (r = 0.24). Olfactory threshold results are only marginally influenced by age (r = 0.18) and are not associated with cognitive test performance. Olfactory assessment using olfactory threshold and "U-Sniff" odor identification testing is suitable for children and adolescents when considering age in the interpretation of test results.

Prefrontal Responses to Odors in Individuals With Autism Spectrum Disorders: Functional NIRS Measurement Combined With a Fragrance Pulse Ejection System

Individuals with autism spectrum disorders (ASD) are impaired not only in social competencies but also in sensory perception, particularly olfaction. The olfactory ability of individuals with ASD has been examined in several psychophysical studies, but the results have been highly variable, which might be primarily due to methodological difficulties in the control of odor stimuli (e.g., the problem of lingering scents). In addition, the neural correlates of olfactory specificities in individuals with ASD remain largely unknown. To date, only one study has investigated this issue using functional magnetic resonance imaging (fMRI). The present study utilized a sophisticated method-a pulse ejection system-to present well-controlled odor stimuli to participants with ASD using an ASD-friendly application. With this advantageous system, we examined their odor detection, identification, and evaluation abilities and measured their brain activity evoked by odors using functional near-infrared spectroscopy (fNIRS). As the odor detection threshold (DT) of participants with ASD was highly variable, these participants were divided into two groups according to their DT: an ASD-Low DT group and an ASD-High DT group. Behavioral results showed that the ASD-High DT group had a significantly higher DT than the typically developing (control) group and the ASD-Low DT group, indicating their insensitivity to the tested odors. In addition, while there was no significant difference in the odor identification ability between groups, there was some discrepancy between the groups' evaluations of odor pleasantness. The brain data identified, for the first time, that neural activity in the right dorsolateral prefrontal cortex (DLPFC) was significantly weaker in the ASD-High DT group than in the control group. Moreover, the strength of activity in the right DLPFC was negatively correlated with the DT. These findings suggest that participants with ASD have impairments in the higher-order function of olfactory processing, such as olfactory working memory and/or attention.

Differences in Mechanisms of Steroid Therapy and Olfactory Training for Olfactory Loss in Mice

Objective

Steroid therapy and olfactory training are common treatments for olfactory loss. Systemic steroid treatment is the most effective approach for treating sinonasal olfactory loss. Olfactory training is typically effective for treating sensorineural olfactory loss. However, the differences in mechanisms of steroid therapy and olfactory training for olfactory dysfunction are unclear. The aim of this study was thus to evaluate the differences in mechanisms of olfactory training and steroid therapy.

Subjects and Methods

Mice in each group were administered 3-methylindole at a dose of 300 mg/kg. Olfactory function was evaluated with a food-finding test once a week. The olfactory neuroepithelium was harvested for histologic examination and protein analysis. Subsequently, data analysis, gene ontology and pathway analysis, quantitative real-time polymerase chain reaction of mRNA, and western blot analysis were conducted.

Results

Mice were divided into four groups according to treatment. Control, anosmia, training, and steroid groups resumed food-finding. MMP27, CCL22 and IL18rap mRNA expression were significantly increased in the training group compared to that in the steroid group. IL1R2 mRNA expression was significantly higher in the olfactory neuroepithelium of steroid-treated mice than in that of the training group mice.

Conclusions

Steroid therapy improved olfactory function via anti-inflammatory effects, unlike olfactory training which involved cell regeneration and tissue remodeling. Protein and gene analyses revealed that steroid therapy and olfactory training are underpinned by distinct mechanisms. Selection of the most appropriate treatment will be dependent on the cause of olfactory loss.

Limitations in odour simulation may originate from differential sensory embodiment

Across diverse lineages, animals communicate using chemosignals, but only humans communicate about chemical signals. Many studies have observed that compared with other sensory modalities, communication about smells is relatively rare and not always reliable. Recent cross-cultural studies, on the other hand, suggest some communities are more olfactorily oriented than previously supposed. Nevertheless, across the globe a general trend emerges where olfactory communication is relatively hard. We suggest here that this is in part because olfactory representations are different in kind: they have a low degree of embodiment, and are not easily expressed as primitives, thereby limiting the mental manipulations that can be performed with them. New exploratory data from Dutch children (9-12 year-olds) and adults support that mental imagery from olfaction is weak in comparison with vision and audition, and critically this is not affected by language development. Specifically, while visual and auditory imagery becomes more vivid with age, olfactory imagery shows no such development. This is consistent with the idea that olfactory representations are different in kind from representations from the other senses. This article is part of the Theo Murphy meeting issue 'Olfactory communication in humans'.

The neuroplastic effect of olfactory training to the recovery of olfactory system in mouse model

Background

Several studies have reported the benefits of olfactory training (OT) in the olfactory nervous system of mouse models. Therefore, in this study we performed next‐generation sequencing to evaluate the effects of OT on mRNA sequencing in the olfactory area.

Methods

Mice in each group were administered 300 mg of 3‐methylindole per kilogram of mouse weight. The olfactory function was evaluated by a food‐finding test once a week. The olfactory neuroepithelium was harvested for histologic examination and protein analysis. Subsequently, data analysis, gene ontology and pathway analysis, quantitative real‐time polymerase chain reaction of mRNA, and Western blot analysis were conducted.

Results

Mice were divided into 4 groups according to treatment. Control, anosmia, training, and steroid group mice resumed food finding. Olfactory Maker Protein, olfr1507, ADCY3, and GNAL mRNA expression was higher in the olfactory neuroepithelium of OT than anosmia group mice. In total, 26,364 mRNAs were analyzed. Comparison of the results of OT vs anosmia revealed that ADCY8,10, GFAP, NGF, NGFR, GFAP, and BDNF mRNAs were upregulated in the gene ontology.

Conclusion

OT improved olfactory function, as indicated by the food‐finding test. OT improved the olfactory recovery time to stimulate olfactory nerve regeneration. OT may initially stimulate the olfactory receptor, followed by neurogenesis. Steroid therapy and OT operated under completely different mechanisms in the upregulated gene study. These results indicate that OT may be one of the future modalities for treating olfactory impairment.

Psycholinguistic variables matter in odor naming

People from Western societies generally find it difficult to name odors. In trying to explain this, the olfactory literature has proposed several theories that focus heavily on properties of the odor itself but rarely discuss properties of the label used to describe it. However, recent studies show speakers of languages with dedicated smell lexicons can name odors with relative ease. Has the role of the lexicon been overlooked in the olfactory literature? Word production studies show properties of the label, such as word frequency and semantic context, influence naming; but this field of research focuses heavily on the visual domain. The current study combines methods from both fields to investigate word production for olfaction in two experiments. In the first experiment, participants named odors whose veridical labels were either high-frequency or low-frequency words in Dutch, and we found that odors with high-frequency labels were named correctly more often. In the second experiment, edibility was used for manipulating semantic context in search of a semantic interference effect, presenting the odors in blocks of edible and inedible odor source objects to half of the participants. While no evidence was found for a semantic interference effect, an effect of word frequency was again present. Our results demonstrate psycholinguistic variables—such as word frequency—are relevant for olfactory naming, and may, in part, explain why it is difficult to name odors in certain languages. Olfactory researchers cannot afford to ignore properties of an odor’s label.

Changes in olfactory bulb volume following lateralized olfactory training

Repeated exposure to odors modifies olfactory function. Consequently, "olfactory training" plays a significant role in hyposmia treatment. In addition, numerous studies show that the olfactory bulb (OB) volume changes in disorders associated with olfactory dysfunction. Aim of this study was to investigate whether and how olfactory bulb volume changes in relation to lateralized olfactory training in healthy people. Over a period of 4 months, 97 healthy participants (63 females and 34 males, mean age: 23.74 ± 4.16 years, age range: 19-43 years) performed olfactory training by exposing the same nostril twice a day to 4 odors (lemon, rose, eucalyptus and cloves) while closing the other nostril. Before and after olfactory training, magnetic resonance imaging (MRI) scans were performed to measure OB volume. Furthermore, participants underwent lateralized odor threshold and odor identification testing using the "Sniffin' Sticks" test battery.OB volume increased significantly after olfactory training (11.3 % and 13.1 % respectively) for both trained and untrained nostril. No significant effects of sex, duration and frequency of training or age of the subjects were seen. Interestingly, PEA odor thresholds worsened after training, while olfactory identification remained unchanged.These data show for the first time in humans that olfactory training may involve top-down process, which ultimately lead to a bilateral increase in olfactory bulb volume.

Development of an International Odor Identification Test for Children: The Universal Sniff Test

OBJECTIVE

To assess olfactory function in children and to create and validate an odor identification test to diagnose olfactory dysfunction in children, which we called the Universal Sniff (U-Sniff) test.

STUDY DESIGN

This is a multicenter study involving 19 countries. The U-Sniff test was developed in 3 phases including 1760 children age 5-7 years. Phase 1: identification of potentially recognizable odors; phase 2: selection of odorants for the odor identification test; and phase 3: evaluation of the test and acquisition of normative data. Test-retest reliability was evaluated in a subgroup of children (n = 27), and the test was validated using children with congenital anosmia (n = 14).

RESULTS

Twelve odors were familiar to children and, therefore, included in the U-Sniff test. Children scored a mean ± SD of 9.88 ± 1.80 points out of 12. Normative data was obtained and reported for each country. The U-Sniff test demonstrated a high test-retest reliability (r₂₇ = 0.83, P < .001) and enabled discrimination between normosmia and children with congenital anosmia with a sensitivity of 100% and specificity of 86%.

CONCLUSIONS

The U-Sniff is a valid and reliable method of testing olfaction in children and can be used internationally.

Olfactory perception in children

The ability to smell is important for protection from danger and quality of life, even in children. Although smell loss is rare in children, it can be indicative of some childhood disorders and may be useful for understanding some disorders. This paper reviews the methods and results of behavioral testing olfaction in children, with an emphasis on odor identification, the most common method of assessing the sense of smell in both children and adults. The Pediatric Smell Wheel® is described as a relatively new and powerful tool for testing olfaction in children as young as 4 years of age. An example of its use in testing children with a childhood disorders (autism spectrum disorder, ASD) is provided in addition to a review of the literature on smell function in ASD. It is possible to reliably test sense of smell in children as young as 4 years old and many studies have shown that performance improves with age and can be impacted by childhood disorders. Sex differences in children are briefly discussed. Finally, the paper suggests other methods of testing olfaction in children, such as odor discrimination, that depend less on cognitive factors, which may enhance our understanding of the olfactory capabilities of young children.

Developmental Fine-tuning of Human Olfactory Discriminability

Unlike vision or audition, human olfaction is generally considered evolutionarily ancient and well-functioning at birth, yet there have been few empirical data on the development of olfactory acuity. The current study has assessed olfactory discriminability in children aged 3 to 6 years with 16 pairs of single-compound odorants that differ in various degrees in structure and smell. We report a significant improvement over age in young children's overall olfactory discriminability. Critically, such improvement is modulated by the degree of structural similarity between odorants independent of odor familiarity. Our findings indicate that odor representations in the olfactory system are fine-tuned during early childhood (3-6 years of age) to allow refined discrimination. Moreover, they suggest the need to take molecular similarity into consideration in the evaluation of olfactory discrimination in pediatric populations.

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.

Odor detection thresholds in a population of older adults

OBJECTIVES/HYPOTHESIS

To measure odor detection thresholds and associated nasal and behavioral factors in an older adult population.

STUDY DESIGN

Cross-sectional cohort study.

METHODS

Odor detection thresholds were obtained using an automated olfactometer on 832 participants, aged 68 to 99 (mean age = 77) years in the 21-year (2013-2016) follow-up visit of the Epidemiology of Hearing Loss Study.

RESULTS

The mean odor detection threshold (ODT) score was 8.2 (range = 1-13; standard deviation = 2.54), corresponding to an n-butanol concentration of slightly less than 0.03%. Older participants were significantly more likely to have lower (worse) ODT scores than younger participants (P < .001). There were no significant differences in mean ODT scores between men and women. Older age was significantly associated with worse performance in multivariable regression models, and exercising at least once per week was associated with reduced odds of having a low (≤5) ODT score. Cognitive impairment was also associated with poor performance, whereas a history of allergies or a deviated septum was associated with better performance.

CONCLUSIONS

Odor detection threshold scores were worse in older age groups but similar between men and women in this large population of older adults. Regular exercise was associated with better odor detection thresholds, adding to the evidence that decline in olfactory function with age may be partly preventable.

LEVEL OF EVIDENCE

3b. Laryngoscope, 127:1257-1262, 2017.

Individual Differences in Verbal and Non-Verbal Affective Responses to Smells: Influence of Odor Label Across Cultures

Olfactory perception is highly variable from one person to another, as a function of individual and contextual factors. Here, we investigated the influence of 2 important factors of variation: culture and semantic information. More specifically, we tested whether cultural-specific knowledge and presence versus absence of odor names modulate odor perception, by measuring these effects in 2 populations differing in cultural background but not in language. Participants from France and Quebec, Canada, smelled 4 culture-specific and 2 non-specific odorants in 2 conditions: first without label, then with label. Their ratings of pleasantness, familiarity, edibility, and intensity were collected as well as their psychophysiological and olfactomotor responses. The results revealed significant effects of culture and semantic information, both at the verbal and non-verbal level. They also provided evidence that availability of semantic information reduced cultural differences. Semantic information had a unifying action on olfactory perception that overrode the influence of cultural background.

Odour Perception: An Object-Recognition Approach

Object recognition is a crucial component of both visual and auditory perception. It is also critical for olfaction. Most odours are composed of 10s or 100s of volatile components, yet they are perceived as unitary perceptual events against a continually shifting olfactory background (ie figure—ground segregation). We argue here that this occurs by rapid central adaptation to background odours combined with a pattern-matching system to recognise discrete sets of spatial and temporal olfactory features—an odour object. We present supporting neuropsychological, learning, and developmental evidence and then describe the neural circuitry which underpins this. The vagaries of an object-recognition approach are then discussed, with emphasis on the putative importance of memory, multimodal representations, and top—down processing.

[Clinical and MRI Findings in Patients with Congenital Anosmia]

The clinical characteristics of 16 patients with congenital anosmia were examined retrospectively. MRI (magnetic resonance imaging) was used to assess the morphological changes in the olfactory bulbs and olfactory sulci according to the method of P. Rombaux (2009). Congenital anosmia was divided into two forms: syndromic forms in association with a syndrome, and isolated forms without evidence of other defects. Only three patients (19%) in our series had syndromic forms of congenital anosmia, such as the Kallmann syndrome. Most cases (13 patients, 81%) had isolated congenital anosmia. Psychophysical testing of the olfactory function included T&T olfactometry and the intravenous Alinamin test, which are widely used in Japan. In T&T olfactometry, detection and recognition thresholds for the five odorants are used to assign a diagnostic category representing the level of olfactory function. Most cases (14 patients, 88%) showed off-scale results on T&T olfactometry, and the Alinamin test resulted in no response in all 11 patients who underwent the test. Abnormal MRI findings of the olfactory bulbs and sulci were detected in 15 of 16 patients (94%). Olfactory bulbs were bilaterally absent in nine patients (56%), and two patients (13%) had unilateral olfactory bulbs. Four patients (25%) had bilateral hypoplastic olfactory bulbs, and only one patient had normal olfactory bulbs (6%). The olfactory sulcus was unilaterally absent in one patient (6%), and nine patients (56%) had bilaterally hypoplastic olfactory sulci. Two patients (13%) had a unilateral normal olfactory sulcus and hypoplastic olfactory sulcus. Three patients (19%) had normal olfactory sulci. Quantitative analysis showed that the volume of olfactory bulbs varied from 0 mm3 to 63.5 mm3, with a mean volume of 10.20 ± 18 mm3, and the mean depth of the olfactory sulcus varied from 0 mm to 12.22 mm, with a mean length of 4.85 ± 4.1 mm. Currently, there is no effective treatment for congenital anosmia. However, diagnosis of congenital anosmia is important, as its presence can lead to dangerous situations. Careful examination for hypogonadism is also required in people with anosmia. MRI examinations of the olfactory bulbs and sulci were useful for the diagnosis of congenital anosmia.

Longitudinal Changes in Familiarity, Free and Cued Odor Identification, and Edibility Judgments for Odors in Aging Individuals

This longitudinal study investigated changes in olfaction as assessed by a set of tasks requiring different aspects of semantic information in normal aging individuals. Using 16 odorous items from a standardized olfactory test, the Scandinavian Odor Identification Test, 107 middle aged and older adults were assessed up to three times over a period of 6.5 years, requesting them to rate familiarity and edibility for each odorous item before identifying it with or without presenting verbal cues. Using linear mixed models, the longitudinal analyses revealed significant correlations between all olfactory measures. Furthermore, we found an almost parallel age-related decline in all olfactory tasks, although free identification performance indicated a trend toward faster decline with age. Women showed less decline compared with men, in particular for edibility judgments. The results corroborate earlier cross-sectional findings showing significant correlations between the olfactory tasks. In the present study of healthy middle-aged and older adults, we found a parallel longitudinal decline across different tests of olfaction.

Olfactory drug effects approached from human-derived data

The complexity of the sense of smell makes adverse olfactory effects of drugs highly likely, which can impact a patient's quality of life. Here, we present a bioinformatics approach that identifies drugs with potential olfactory effects by connecting drug target expression patterns in human olfactory tissue with drug-related information and the underlying molecular drug targets taken from publically available databases. We identified 71 drugs with listed olfactory effects and 147 different targets. Taking the target-based approach further, we found additional drugs with potential olfactory effects, including 152 different substances interacting with genes expressed in the human olfactory bulb. Our proposed bioinformatics approach provides plausible hypotheses about mechanistic drug effects for drug discovery and repurposing and, thus, would be appropriate for use during drug development.

Changes of olfactory abilities in relation to age: odor identification in more than 1400 people aged 4 to 80 years

The currently presented large dataset (n = 1,422) consists of results that have been assembled over the last 8 years at science fairs using the 16-item odor identification part of the “Sniffin’ Sticks”. In this context, the focus was on olfactory function in children; in addition before testing, we asked participants to rate their olfactory abilities and the patency of the nasal airways. We reinvestigated some simple questions, e.g., differences in olfactory odor identification abilities in relation to age, sex, self-ratings of olfactory function and nasal patency. Three major results evolved: first, consistent with previously published reports, we found that identification scores of the youngest and the oldest participants were lower than the scores obtained by people aged 20–60. Second, we observed an age-related increase in the olfactory abilities of children. Moreover, the self-assessed olfactory abilities were related to actual performance in the smell test, but only in adults, and self-assessed nasal patency was not related to the “Sniffin’ Sticks” identification score.

Food neophobia and its relation with olfaction

Food neophobia, that is the reluctance to try novel foods, is an attitude that dramatically affects human feeding behavior in many different aspects among which food preferences and food choices appear to be the most thoroughly considered. This attitude has an important evolutionary meaning since it protects the individual from ingesting potentially dangerous substances. On the other hand, it fosters an avoidance behavior that can extend even toward useful food elements. A strong link exists between food neophobia and both the variety in one person’s diet and previous exposures to different foods. In this review, the more recent findings about food neophobia will be concisely described. Given the suggested connection between the exposure to different foods and food neophobia, this review will focus on the relation between this attitude and human chemosensory abilities. Olfaction, in particular, is a sensory modality that has a central role in flavor perception and in food preference acquisition. Therefore, the latest evidences about its relation with food neophobia will be discussed along with the applied and cognitive implications.

Olfactory training in patients with Parkinson's disease

OBJECTIVE

Decrease 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.

METHODS

We 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.

RESULTS

Compared 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.

CONCLUSION

The present results indicate that olfactory training may increase olfactory sensitivity in PD patients.

Odor identification testing in children and young adults using the smell wheel

OBJECTIVE

Olfaction is important for nutrition, safety, and quality of life. Detecting smell loss in young children can be difficult, since many children with olfactory deficits do not recognize their problem and may even pretend to smell. The short attention span of some young children precludes testing with longer standardized olfactory tests. Currently there is a dearth of pediatric smell tests. In this study we evaluated the performance of 152 children and young adults on a game-like rotating "Smell Wheel" odor identification test. This forced-choice test, which can be self-administered, was designed to capture the child's imagination and to provide a standardized test measure with odors known to young children using a minimum number of trials.

METHOD

Thirty 4-5-year olds (10 female), 62 6-7-year olds (17 female), 30 10-11-year olds (18 female) and 30 18-19-year olds (15 female) were tested. Analysis of variance was used to assess the influences of sex and age on the test scores.

RESULTS

All participants completed the simple and rapid test protocol. Test performance and age-related changes analogous to those obtained using longer tests were observed. Test scores of participants who self-administered the test were equivalent to those for whom the test was administered by the experimenter.

CONCLUSION

Good compliance and olfactory test findings congruent with literature results were obtained using the Smell Wheel, suggesting that this test may be useful in assessing olfactory function in pediatric settings where attentional demands are compromised and test time is limited.

Correlation between olfactory bulb volume and olfactory function in children and adolescents

The olfactory bulb (OB) is considered to be the most important relay station in odor processing. The present study aimed to investigate the volumetric development of the human bulb and the olfactory function during childhood and youth. Furthermore, the present study aimed to investigate a possible correlation between OB volume and specific olfactory functions including odor threshold, odor discrimination and odor identification. A total of 87 subjects (46 boys, 41 girls), aged 1-17 years (mean age 8 years), participated in this study. None of them reported olfactory dysfunction or had signs of a dysfunctional sense of smell. Whenever possible, participants received a volumetric scan of the brain and lateralized olfactory tests. Volumetric measurements of the right and left OB were taken by manual segmentation of the coronal slices through the OB. Significant correlations between OB volumes and olfactory function were observed. Both, OB volumes and olfactory function increased with age, although the correlation between structure and function was not mediated by the subjects' age. In conclusion, for the first time, the present study showed a correlation between OB volume and olfactory functions in children.

Olfactory sensitivity: functioning in schizophrenia and implications for understanding the nature and progression of psychosis

Prefrontal neural processes maturing during neurodevelopment parallel normal improvement in higher order olfactory processing (identification) from childhood. Hence, disorders of adolescence such as schizophrenia that implicate prefrontal regions are associated with olfactory identification deficits in the presence of relatively intact lower order olfactory processing capacity (sensation) and mediating neural processes (limbic system). Understanding the linear neural trajectory of olfactory processing can assist in detecting the location, nature, and extent of early compromise of circuitry implicated in neurodevelopmental disorders such as psychosis. More recently, relatively discreet odorant sensitivity problems in schizophrenia have been described and these appear related to secretion of malodorous compounds. These findings have significant implications for future genetic prediction of this disorder.

Developmental differences in memory for cross-modal associations

Associative learning is critical to normal cognitive development in children. However, young adults typically outperform children on paired-associate tasks involving visual, verbal and spatial location stimuli. The present experiment investigated cross-modal odour-place associative memory in children (7-10 years) and young adults (18-24 years). During the study phase, six odours were individually presented and paired with one of 12 spatial locations on a board. During the test phase, participants were presented with the six stimuli individually and were asked to place each stimulus on the correct spatial location. Children committed significantly more errors on the odour-place task than did young adults. However, item recognition memory for the odours or spatial locations involved in the odour-place associative memory task was similar between children and young adults. Therefore, poor odour-place associative memory in children did not result from impaired memory for the individual odours or spatial locations involved in the associations. The results suggest that cross-modal associative memory is not fully developed in children.