The influences of age on olfaction: a review

Neurogenesis dynamics in the olfactory bulb: deciphering circuitry organization, function, and adaptive plasticity

Adult neurogenesis persists after birth in the subventricular zone, with new neurons migrating to the granule cell layer and glomerular layers of the olfactory bulb, where they integrate into existing circuitry as inhibitory interneurons. The generation of these new neurons in the olfactory bulb supports both structural and functional plasticity, aiding in circuit remodeling triggered by memory and learning processes. However, the presence of these neurons, coupled with the cellular diversity within the olfactory bulb, presents an ongoing challenge in understanding its network organization and function. Moreover, the continuous integration of new neurons in the olfactory bulb plays a pivotal role in regulating olfactory information processing. This adaptive process responds to changes in epithelial composition and contributes to the formation of olfactory memories by modulating cellular connectivity within the olfactory bulb and interacting intricately with higher-order brain regions. The role of adult neurogenesis in olfactory bulb functions remains a topic of debate. Nevertheless, the functionality of the olfactory bulb is intricately linked to the organization of granule cells around mitral and tufted cells. This organizational pattern significantly impacts output, network behavior, and synaptic plasticity, which are crucial for olfactory perception and memory. Additionally, this organization is further shaped by axon terminals originating from cortical and subcortical regions. Despite the crucial role of olfactory bulb in brain functions and behaviors related to olfaction, these complex and highly interconnected processes have not been comprehensively studied as a whole. Therefore, this manuscript aims to discuss our current understanding and explore how neural plasticity and olfactory neurogenesis contribute to enhancing the adaptability of the olfactory system. These mechanisms are thought to support olfactory learning and memory, potentially through increased complexity and restructuring of neural network structures, as well as the addition of new granule granule cells that aid in olfactory adaptation. Additionally, the manuscript underscores the importance of employing precise methodologies to elucidate the specific roles of adult neurogenesis amidst conflicting data and varying experimental paradigms. Understanding these processes is essential for gaining insights into the complexities of olfactory function and behavior.

Aging and chronic inflammation: impacts on olfactory dysfunction-a comprehensive review

Olfactory dysfunction (OD) is a common nasal disease, particularly prevalent among the elderly population, significantly impacting the affected individuals' quality of life. This review focuses on the influence of aging and chronic inflammation on olfactory dysfunction, presenting insights from both the peripheral and central olfactory systems. By exploring the molecular mechanisms and pathological changes underlying the occurrence of olfactory dysfunction in relation to age-related diseases and chronic inflammation conditions, we aim to provide a comprehensive theoretical foundation for further research and offer valuable insights for more effective treatment of olfactory dysfunction.

Long-term exposure to traffic-related air pollution is associated with impaired odor identification: Results from the population-based KORA FIT study in Augsburg, Germany

Ambient air pollution has been linked to neurodegenerative diseases. Nevertheless, the literature on the effects of air pollution on the olfactory system and early cognitive impairment is scarce. In this study, we investigated the association between long-term air pollution exposure and odor identification, which can serve as an early indicator of various neurodegenerative conditions. We used data collected in Augsburg, Germany in 2018-2019 for the population-based KORA FIT study of 3,059 participants born between 1945-1964. The Sniffin' Sticks 12-Item Test was used to assess each participant's odor identification. Air pollution concentrations at residential addresses were estimated using land use regression modeling. We dichotomized the odor identification score to normosmia (score ≥ 10) versus hyposmia (score < 7) or anosmia (score < 10) and applied logistic regression. The models were adjusted for age, sex, socioeconomic characteristics (education, income, socioeconomic status), lifestyle factors (physical activity, smoking, body mass index, alcohol consumption) and disease history (e.g., allergies). We observed increased odds of hyposmia or anosmia compared to normosmia per interquartile range increase in the concentrations of PNC, PM2.5, PM2.5abs, PMcoarse, PM10, NO2 and NOx [OR (95 % CI): 1.12 (1.02, 1.24), 1.10 (0.98, 1.25), 1.14 (1.00, 1.30), 1.20 (1.06, 1.35), 1.20 (1.06, 1.36), 1.20 (1.06, 1.37) and 1.13 (1.01, 1.27); respectively]. For O3, no clear effects were detected. Females and physically active people appeared to be more susceptible. No further significant indications of effect modification were found. The results were consistent across sensitivity analyses. This study provides robust evidence for an association between long-term exposure to traffic-related air pollution and poor odor identification, even in a region with relatively low air pollution levels. These findings suggest a potential link between prolonged air pollution exposure and early changes in the olfactory system and could be indicative of early signs of detrimental effects on the brain.

Development of a Southeast Asian version of the "Sniffin Sticks" odor identification test

INTRODUCTION

The odor identification test is an efficient and rapid way to assess and screen a patient's sense of smell. The original Sniffin' Sticks odor identification test (SST) consisted of 16 smells developed for a European population. However, this identification test can be influenced by cultural differences, such as variations in food culture, ethnicity and language. We propose developing a test that uses odors more familiar and specific to the Association of Southeast Asian Nations (ASEAN) population.

METHODS

The study involved four stages: (1) A familiarity questionnaire to select odors, (2) Testing of selected odors on healthy participants from different regions, (3) Application of the developed test on healthy subjects and those with smell disorders, and (4) Test-retest reliability assessment. A total of 466 participants aged 16 to 87 years were involved across all stages. The final ASEAN Sniffin' Sticks odor identification test (ASST) was conducted on 106 healthy subjects (HS) and 68 subjects with smell disorders, including 29 with Parkinson's disease (PD) and 39 with sinonasal diseases (Ear, Nose, and Throat [ENT]).

RESULTS

Mean scores of 15.75 ± 0.62 were found in the HS group, 9.07 ± 3.67 in the PD group, and 10.90 ± 4.87 in the ENT group, out of a total possible score of 16. The 10th percentile value (score of 15) in HS aged 17-35 was used as cutoff between normal olfaction from those with a smell disorder. There were significant differences between the HS group and both the PD and ENT groups (p < 0.001), but no significant difference was found between the PD and ENT groups (p = 0.068). The ASST demonstrated high test-retest reliability, with a correlation (r) = 0.92 (p < 0.001).

CONCLUSION

The ASST provides a reliable tool for evaluating olfactory function and detecting olfactory loss associated with various conditions in the ASEAN region.

Anatomy, histology and ultrastructure of the adult human olfactory peduncle: Blood vessel and corpora amylacea assessment

The mammalian olfactory system is responsible for processing environmental chemical stimuli and comprises several structures, including the olfactory epithelium, olfactory bulb, olfactory peduncle (OP), and olfactory cortices. Despite the critical role played by the OP in the conduction of olfactory information, it has remained understudied. In this work, optical, confocal, and electron microscopy were employed to examine the anatomy, histology, and ultrastructure of six human OP specimens (ages 37-84 years). Three concentric layers were identified in coronal sections: the external layer (EL), the axonal layer (AL), and the internal layer (IL). Immunohistochemistry revealed the distribution of neurons and glial cells throughout the OP. Two neuronal morphologies were observed: granule cells and larger pyramidal cells, the latter associated with projection neurons of the anterior olfactory nucleus. Astrocytes were uniformly distributed with a more radial morphology in the EL. Oligodendrocytes were mainly located in the AL. Blood vessels (BVs) were evenly distributed along the OP, with a mean luminal area of 82.9 µm² and a density of 1.26 %, with a significant increase in the IL. Corpora amylacea (CA) were abundant, with an average size of 49.3 µm² and a density of 3.23 %. CA clustered near BVs, particularly at tissue edges, with both size and density increasing with age. Notably, CA showed strong associations with astrocytes. This study provides the first detailed qualitative and quantitative data on the internal organization of the human OP, which may contribute to a better understanding of the pathophysiology of some neuropathological disorders.

Investigating the Evolution of Odor-Evoked Memories Retrieval in Normal Aging: Theoretical and Clinical Implications

BACKGROUND

Olfactory-based cognitive stimulation is frequently proposed for memory-impaired patients (namely dementia patients), but little is known about the scientific rationale underlying odor choice.

OBJECTIVES

Here, we aimed at investigating the evolution of the olfactory experience related to memory evocation in normal aging. Methods. We presented 20 odorants to 25 Young Adults (YA), 36 "young" Older Adults (OA; 65 - 74y) and 26 "old" OA (75 - 89y) and asked them to freely report what each odor evoked to them. Responses were analyzed using both univariate inferential statistics and multivariate descriptive analysis.

RESULTS

Results showed that the ability to experience phenomenological properties of evoked memories decreases with advancing age. Odor identity is increasingly used as a retrieval cue with age, providing necessary support for OA retrieval strategies. However, semantic information does not enhance the chances for old-OA to experience memories' phenomenological properties.

CONCLUSION

Tailoring the choice of odors during stimulating activities is therefore crucial. In this respect, we provided a limited selection of the most well-characterized odorous stimuli and sorted them based on the phenomenological experience they're more likely to trigger across ages.

Six-week engagement in after-school activities involving chemosensory education does not affect olfactory abilities and personal significance of olfaction in 9-11-year-olds: Preliminary evidence

Chemosensory learning is a lifelong process of acquiring perceptual expertise and semantic knowledge about chemical stimuli within the everyday environment. In the research context, it is usually simulated using olfactory training, which typically involves repeated exposure to a set of odors over a period of time. Following olfactory training, enhanced olfactory performance has been observed in adults, and similar evidence is beginning to emerge in children. However, the literature is scant concerning the effects of interventions that more closely resemble how chemosensory experience is acquired in daily life. Since children's chemosensory ecology appears to play a crucial role in olfactory development, we investigated whether engaging in activities that stimulate the chemical senses enhances olfactory performance and metacognition. To this end, we invited 20 children aged 9-11 years to participate in teacher-assisted after-school activities for 30-60 minutes a day for six weeks. During the odd weeks, the children appraised herbal and spice blends and used them to prepare dishes and make beauty products. During the even ones, they explored the city by smellwalking and created smellscape maps. The educational outcomes were evaluated using the Sniffin' Sticks test for odor identification and discrimination and the Children's Personal Significance of Olfaction. Bayesian analyses did not reveal any compelling evidence in support of the alternative hypothesis that children in the chemosensory education group outperform those in the comparison group at the post-test. Rates of reliable increase but also decrease in performance on the Sniffin' Sticks identification and discrimination tests were similar in both groups. We corroborated the previous findings regarding girls' and older children's greater proficiency at identifying odors and the female keener interest in the sense of smell. We offer several practical suggestions researchers may want to consider to tailor their research protocols to reflect more closely the broader context in which chemosensory learning takes place and better capture the nuanced outcomes of such interventions.

Olfactory Testing and Gray Matter Volume: A Combined Approach to Predict the Conversion to Alzheimer

Background/Objectives: Olfactory decline is common in normal aging and frequent in neurodegenerative diseases such as Alzheimer's disease (AD). Therefore, it has been suggested as a marker for the Mild Cognitive Impairment (MCI) progression to AD. Although suggested, the relationship between olfactory deficits and cerebral atrophy in MCI conversion to AD is still debated. This study aims at investigating the olfaction-related morphological and behavioural alterations in MCI in order to understand whether they can predict the progression to AD. Methods: Twenty-seven MCI patients and thirty-five healthy controls (HCs) took part in the study, with follow-up showing conversion to AD in thirteen patients (converter-MCI, cMCI). The Burgarth Sniffin' Sticks Tests (threshold-TT, discrimination-DT, identification-IT) assessed the olfactory capacities. The Voxel-Based Morphometry (VBM) analysis investigated the atrophic patterns. Results: The Receiving Operating Characteristics analyses demonstrated that DT and IT could distinguish HC from MCI (DT Area Under Curve-AUC = 0.8; IT AUC = 0.8), as well as cMCI from sMCI (stable) patients (DT AUC = 0.7; IT AUC = 0.6), similarly to memory and executive functions tests. Olfactory performance positively correlated with memory tests in sMCI (all rhos ≥ 0.8, all ps < 0.01), whereas it positively correlated with executive functions in cMCI (all rhos ≥ 0.6, all ps < 0.05). VBM results revealed distinct atrophic patterns in cMCI, especially in the olfactory cortex, that were already present at the MCI diagnosis, before AD conversion. A larger volume of the olfactory cortex was associated with better memory and executive functions. Conclusions: Quantitative olfactory and morphological patterns represent non-invasive, predictive biomarkers of the MCI progression to AD; thus, their assessments at MCI onset allows earlier interventions for MCI patients.

Olfactory Dysfunction as a Clinical Marker of Early Glymphatic Failure in Neurodegenerative Diseases

An abnormal accumulation of misfolded proteins is a common feature shared by most neurodegenerative disorders. Olfactory dysfunction (OD) is common in the elderly population and is present in 90% of patients with Alzheimer's or Parkinson's disease, usually preceding the cognitive and motor symptoms onset by several years. Early Aβ, tau, and α-synuclein protein aggregates deposit in brain structures involved in odor processing (olfactory bulb and tract, piriform cortex, amygdala, entorhinal cortex, and hippocampus) and seem to underly OD. The glymphatic system is a glial-associated fluid transport system that facilitates the movement of brain fluids and removes brain waste during specific sleep stages. Notably, the glymphatic system became less functional in aging and it is impaired in several conditions, including neurodegenerative diseases. As the nasal pathway has been recently described as the main outflow exit of cerebrospinal fluid and solutes, we hypothesized that OD may indeed be a clinical marker of early glymphatic dysfunction through abnormal accumulation of pathological proteins in olfactory structures. This effect may be more pronounced in peri- and postmenopausal women due to the well-documented impact of estrogen loss on the locus coeruleus, which may disrupt multiple mechanisms involved in glymphatic clearance. If this hypothesis is confirmed, olfactory dysfunction might be considered as a clinical proxy of glymphatic failure in neurodegenerative diseases.

Longitudinal Association of Olfactory Function with Frailty in Older Adults: The Atherosclerosis Risk in Communities Study

BACKGROUND

Emerging evidence suggests that olfactory dysfunction may be a marker of frailty, a key predictor of adverse health outcomes in aging populations. This study examines the association between olfactory impairment and frailty in older adults.

METHODS

We analyzed data from 5,231 participants (mean age: 75.3 ± 5.0 years; 59% women; 22% Black) of the Atherosclerosis Risk in Communities (ARIC) Study. Olfactory function, assessed using the 12-item Sniffin' Sticks Test at Visit 5 (2011-2013), was categorized as poor (0-8), moderate (9-10), or good (11-12). Frailty status was ascertained using both the Fried Frailty Phenotype and the Cumulative Frailty Index. Cross-sectional associations between olfactory function and frailty status were examined using logistic regression and linear regression. Logistic regression was used to examine the association between olfactory function and prefrailty or frailty occurring within five years among 1,519 participants robust at baseline.

RESULTS

In cross-sectional analyses, good olfactory function was associated with lower odds of frailty (odds ratio [OR] = 0.29, 95% confidence interval [CI]: 0.22, 0.39) and prefrailty (OR = 0.52, 95% CI: 0.45, 0.61). These associations remained robust after adjusting for covariates. Longitudinal analyses similarly showed a dose-response pattern, with improved olfaction associated with decreased odds of experiencing prefrailty (OR=0.63 95% CI [0.48, 0.83]) or frailty (OR=0.50, 95% CI [0.25, 1.02]).

CONCLUSIONS

Good, as compared to poor, olfactory function is associated with lower frailty risk in older adults, suggesting that olfactory impairment may serve as an early marker of frailty. Further research is needed to elucidate the mechanisms linking olfaction and frailty and explore potential interventions.

Non-monotonic psychometric functions for α-ionone in young adults

The mathematical relationship between the ability to detect an odorant and its concentration appears for some odorants to be non-monotonic, with reversals ("notches") in performance appearing at points along the psychometric function. Like visual adaptation curves that reflect the differential sensitivities of cones and rods, such reversals may provide information about underlying olfactory receptor processes. However, the presence of such reversals is rarely acknowledged, few participants and odorants have been tested, and methodological concerns abound. In this study, we examined in detail the psychometric function for the odorant α-ionone using a sizable number of young participants and 10 log-based concentrations of α-ionone presented in a random fashion. A trial consisted of the counterbalanced presentation of an odorless mineral oil and a concentration of α-ionone in rapid succession using Snap & Sniff® wands. The participants reported which of the two seemed stronger and indicated their confidence on a 9-point scale. In Study 1, 24 participants completed a single 30-minute test session of 60 trials. In Study 2, 600 trials were obtained from each of nine participants over the course of ten 30-minute sessions. In both studies, notches were consistently found in the psychometric function near the 10-5 and 10-3.5 vol/vol concentrations. Participants' trial-by-trial confidence judgments corresponded with their detection performance, but their self-rated sense of smell did not. This research definitively demonstrates the presence of reliable reversals in the human α-ionone psychometric function and begs the question as to whether such reversals reflect the recruitment of receptive elements with differing response profiles.

Neurological and Olfactory Disturbances After General Anesthesia

Neurological and olfactory disturbances are increasingly recognized as potential complications of general anesthesia, particularly in vulnerable populations, such as the elderly, children, and individuals with comorbidities. Recent studies have highlighted the need for tailored anesthetic approaches in these high-risk groups to mitigate potential long-term effects. These disturbances, including postoperative cognitive dysfunction, delirium, and olfactory deficits, often arise from shared pathophysiological mechanisms, such as neuroinflammation, oxidative stress, and disruptions in cerebral perfusion. The olfactory system is particularly susceptible to anesthesia-induced neurotoxicity given its proximity to central nervous system structures and its role in sensory and cognitive processing. Furthermore, the unique regenerative capacity of olfactory neurons may be compromised by prolonged or repeated exposure to anesthetic agents, potentially leading to long-term olfactory dysfunction. Risk factors, such as advanced age, neurodegenerative diseases, diabetes, cardiovascular conditions, genetic predispositions, and the type and duration of anesthesia exposure, further exacerbate these complications. Preventive strategies, including comprehensive preoperative risk assessment, personalized anesthetic protocols based on genetic and physiological profiles, and proactive postoperative care with early intervention programs, are critical for reducing impairments and improving long-term patient outcomes. Emerging evidence highlights the potential role of neuroprotective agents, such as antioxidants and anti-inflammatory therapies, in mitigating the effects of anesthesia-induced neurotoxicity. Longitudinal studies are needed to evaluate the long-term effects of anesthesia on cognitive and sensory health, particularly in high-risk populations. These studies should incorporate advanced neuroimaging techniques and biomarker analysis to elucidate the underlying mechanisms of anesthesia-induced neurological and olfactory disturbances. This narrative review provides a comprehensive overview of the mechanisms, risk factors, and preventive strategies for neurological and olfactory disturbances after general anesthesia and highlights future directions for research to improve patient outcomes. We conducted a comprehensive literature search using databases, such as PubMed and Scopus, to identify relevant studies.

Perceptual differences in olfactory fat discrimination are not detected in neural activation

Olfaction is involved in detecting, identifying, and discriminating dietary fat within foods, yet the underlying neural mechanisms remain uncharted. Our functional magnetic resonance imaging (fMRI) study investigated the neural correlates of olfactory fat perception and their association with discrimination ability in a complex food matrix. We measured brain activation resulting from orthonasal exposure to an ecologically relevant fat-related odor source-dairy milk, manipulated to contain 0%, 3.5%, or 14% fat. Twenty-six healthy, normosmic adults underwent olfactory fat content discrimination testing, followed by an fMRI task during which the 3 odor stimuli were delivered via an olfactometer (25 times/fat level) and rated on perceived intensity and liking. Participants discriminated between all fat levels, with fat level influencing perceived odor intensity and liking. These perceptual differences, however, were not reflected in differential brain activation. Brain activation differences were observed only when comparing odor exposure with no exposure. Specifically, in response to any odor, activation occurred in the anterior part of the supplementary motor area (SMA) while deactivating parts of the hippocampus, putamen, superior temporal gyrus, anterior cingulate cortex, insula, and posterior part of the SMA. Exposure to the 0% fat odor also activated the thalamus. No associations were found between perceived intensity and liking and neural responses. Results reaffirm the human ability to distinguish food fat content using solely olfactory cues and reveal a divergence between sensory perception and neural processing. Subsequent research should replicate and extend these findings onto retronasal fat perception while also examining potential effects of hunger, genetics, and dietary habits.

Olfactory dysfunction as potential biomarker in neurodegenerative diseases: a narrative review

Neurodegenerative diseases represent a group of disorders characterized by progressive degeneration of neurons in the central nervous system, leading to a range of cognitive, motor, and sensory impairments. In recent years, there has been growing interest in the association between neurodegenerative diseases and olfactory dysfunction (OD). Characterized by a decline in the ability to detect or identify odors, OD has been observed in various conditions, including Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), and Amyotrophic Lateral Sclerosis (ALS). This phenomenon often precedes the onset of other clinical symptoms, suggesting its potential utility as an early marker or prodromal symptom of neurodegenerative diseases. This review provides a vast literature overview on the current knowledge of OD in PD, AD, ALS, and HD in order to evaluate its potential as a biomarker, particularly in the early and prodromal stages of these diseases. We summarize the most common methods used to measure olfactory function and delve into neuropathological correlations and the alterations in neurotransmitter systems associated with OD in those neurodegenerative diseases, including differences in genetic variants if applicable, and cater to current pitfalls and shortcomings in the research.

An experimental framework for conjoint measures of olfaction, navigation, and motion as pre-clinical biomarkers of Alzheimer's disease

Elucidating Alzheimer's disease (AD) prodromal symptoms can resolve the outstanding challenge of early diagnosis. Based on intrinsically related substrates of olfaction and spatial navigation, we propose a novel experimental framework for their conjoint study. Artificial intelligence-driven multimodal study combining self-collected olfactory and motion data with available big clinical datasets can potentially promote high-precision early clinical screenings to facilitate timely interventions targeting neurodegenerative progression.

Ambient air pollution undermines chemosensory sensitivity - a global perspective

This study offers insights into the complex relationship between chemical species constituting air pollution and chemosensory function. We examined the relationship between chemical species known to contribute to air pollution and assault human health and chemosensory sensitivity. Chemosensory sensitivity data was retrieved from a large-scale study involving 711 urban-dwelling participants inhabiting 10 different regions of the globe. Their olfactory threshold towards phenyl ethyl alcohol (PEA) and olfactory/trigeminal threshold towards Eucalyptol was measured in a multicentre study. We matched the individual chemosensory data with the levels of PM2.5, PM10, O3, NO2, SO2, CO at the location of testing sites, on the exact date of the test, using EMAC (ECHAM5/MESSy for Atmospheric Chemistry) model. Our findings indicate that air pollution negatively affects olfactory function and has cumulative negative effects with aging. The reported patterns are seasonal and increase during Autumn and Winter, and interact with medical conditions related to poorer olfactory function. We extend the current knowledge by demonstrating that olfactory/trigeminal perception is also disrupted by toxic air, albeit in a slightly different manner. The analyzed models promote a more complex perspective on the relationship between air composition and chemosensory sensitivity, but delineate problems related to the interdependence of the levels of chemical species constituting air pollution and using them together to predict chemosensory sensitivity. Conclusions point to the need to investigate the problem of air pollution and chemosensory health from a global perspective, as air quality partly accounts for the differences in chemosensory perception in different regions of the world.

Olfactory deficits in aging and Alzheimer's-spotlight on inhibitory interneurons

Cognitive function in healthy aging and neurodegenerative diseases like Alzheimer's disease (AD) correlates to olfactory performance. Aging and disease progression both show marked olfactory deficits in humans and rodents. As a clear understanding of what causes olfactory deficits is still missing, research on this topic is paramount to diagnostics and early intervention therapy. A recent development of this research is focusing on GABAergic interneurons. Both aging and AD show a change in excitation/inhibition balance, indicating reduced inhibitory network functions. In the olfactory system, inhibition has an especially prominent role in processing information, as the olfactory bulb (OB), the first relay station of olfactory information in the brain, contains an unusually high number of inhibitory interneurons. This review summarizes the current knowledge on inhibitory interneurons at the level of the OB and the primary olfactory cortices to gain an overview of how these neurons might influence olfactory behavior. We also compare changes in interneuron composition in different olfactory brain areas between healthy aging and AD as the most common neurodegenerative disease. We find that pathophysiological changes in olfactory areas mirror findings from hippocampal and cortical regions that describe a marked cell loss for GABAergic interneurons in AD but not aging. Rather than differences in brain areas, differences in vulnerability were shown for different interneuron populations through all olfactory regions, with somatostatin-positive cells most strongly affected.

The digital scent device 20: an automated, self-administered odor identification test

PURPOSE

Assessing olfactory function is highly significant in clinical practice, particularly in the context of the recent COVID-19 pandemic. Recent approaches in this field emphasize the importance of reducing the time and cost devoted to olfactory testing procedures. Hence, the aim of the present study was to examine the reliability and basic characteristics of Digital Scent Device 20 (DSD-20), an innovative olfactory test consisting of 20 "universal odors", in a European population.

METHODS

A total of 88 participants (mean age = 45.1, SD = 20.3) volunteered for the study. The sample consisted of 37 normosmic controls and 51 dysosmic patients.

RESULTS

The correlation between DSD-20 and the total score in Sniffin' Sticks was high (TDI; R = .80, p < .001), and the test correlated with the individual components of the Sniffin' Sticks test. Furthermore, the correlation coefficient between DSD-20 test and retest was very high (R = .88, p < .001), which was additionally confirmed by a Bland-Altman plot. Essential characteristics of the DSD-20 are its simplicity in self-administration, speed of application, portability, and the fact that it can be reused.

CONCLUSION

Overall, the present study confirms previous notions on DSD-20 by demonstrating its high reliability and usefulness in separating patients with hyposmia/anosmia and normosmic controls.

Olfactory Identification as a Biomarker for Cognitive Impairment: Insights from Healthy Aging, Subjective Cognitive Decline, and Mild Cognitive Impairment

Introduction: This study aims to investigate the relationship between olfactory identification (OI) and cognitive impairment by examining OI abilities across various stages of cognitive deterioration. Methods: A total of 264 participants were divided into three groups based on cognitive status: cognitively healthy, subjective cognitive, and mild cognitive impairment. All participants were assessed using the Sniffin' Sticks Olfactory Identification test and a comprehensive neuropsychological test battery. Results: Our results highlight the main effects of age and cognitive status on OI scores. Regarding cognitive abilities, OI is associated with measures of short-term memory, long-term, working memory, and selective attention. Finally, logistic regression models showed that OI is a significant predictor for discriminating SCD from CH, MCI from CH, and MCI from SCD. Discussion: These findings suggest the addition of olfactory identification measures in neuropsychological assessments could improve the early detection of individuals at risk for cognitive impairment.

Differential functional change in olfactory bulb and olfactory eloquent areas in Parkinson's disease

Olfactory dysfunction, or hyposmia, frequently occurs as a prodromal symptom and ongoing sign of Parkinson's disease. Functional MRI is a powerful tool for studying functional changes in the olfactory brain regions in patients with Parkinson's disease. However, existing studies show inconsistent results and no study has measured olfactory functional MRI abnormalities in the human olfactory bulb directly. This is mainly due to the well-known susceptibility artefacts in conventional functional MRI images that affect several key olfactory-eloquent brain regions, and especially the olfactory bulb. In this study, olfactory functional MRI was performed using a recently developed functional MRI approach that can minimize susceptibility artefacts and measure robust functional MRI signals in the human olfactory bulb during olfactory stimulation. Experiments were performed on high magnetic field (7 T) in 24 early (<5 years of parkinsonian symptoms) Parkinson's disease patients and 31 matched healthy controls. Our data showed increased functional MRI signal changes (ΔS/S) in the olfactory bulb in patients with early Parkinson's disease, which correlated with behavioural olfactory measures. Temporally, functional MRI signals in the olfactory bulb returned to the pre-stimulus state earlier after reaching peak amplitude in patients with early Parkinson's disease, implicating a faster olfactory habituation effect. The piriform cortex showed reduced numbers of activated voxels in patients with early Parkinson's disease, which correlated with behavioural olfactory assessment. Several secondary olfactory regions including the orbitofrontal cortex, temporal pole and amygdala exhibited reduced numbers of activated voxels and increased functional MRI signal changes in patients with early Parkinson's disease. Our data also showed that functional MRI results are highly dependent on voxel selection in the functional analysis. In summary, we demonstrate differential spatial and temporal characteristics of olfactory functional MRI signals between the primary and secondary olfactory regions in patients with early Parkinson's disease. These results may assist the development of novel quantitative biomarkers (especially in the early stages of Parkinson's disease) to track and predict disease progression, as well as potential treatment targets for early intervention.

Higher Serum Galectin‑3 Levels Were Associated with More Severe Motor Performance in Parkinson's Disease

Background

Parkinson's disease (PD) is a movement disorder that lacks proven biomarkers. Case-control genome-wide association studies revealed the potential effect of galectin‑3 (GAL3) on motor progression in PD patients. Based on this finding, our study aimed to explore the correlation between serum GAL3 levels and motor performance in PD patients.

Methods

Five hundred PD patients and 200 healthy controls were recruited. The serum levels of GAL3 were measured in participants by enzyme linked immunosorbent assay (ELISA). The baseline characteristics of the participants were collected, and the associated scale scores were obtained.

Results

Compared with healthy controls, the serum levels of GAL3 were greatly increased in PD patients. These levels could distinguish between PD patients and healthy controls with a sensitivity of 0.798 and a specificity of 0.815 (AUC = 0.795, 95% CI 0.757-0.834, P < 0.001). Patients with age >60 years tended to have higher serum GAL3 levels, disease duration, Hoehn-Yahr stage, MDS-UPDRS III total score, tremor subscores, rigid subscores, and bradykinesia subscores than those with age ≤60 years. When adjusting for confounders, higher GAL3 level was significantly correlated with MDS-UPDRS III total score and rigid subscores. In men with PD, GAL3 was significantly correlated with MDS-UPDRS III total score; but the association between GAL3 and bradykinesia subscores was found in women. Moreover, the associations between GAL3 with MDS-UPDRS III total score and bradykinesia subscores were significant in patients with age >60 years.

Conclusion

Higher GAL3 level was related to more severe motor performance in patients with age >60 years, and it may be a potential predictive biomarker for motor performance in PD patients.

Functional connectivity differences of the olfactory network in Parkinson's Disease, mild cognitive impairment and cognitively normal individuals: A resting-state fMRI study

Olfactory dysfunction is an early sign of such neurodegenerative diseases as Parkinson's (PD) and Alzheimer's (AD), and is often present in Mild Cognitive Impairment (MCI), a precursor of AD. Understanding neuro-temporal relationships, i.e., functional connectivity, between olfactory eloquent structures in such disorders, could shed light on their basic pathophysiology. To this end, we employed region-based analyses using resting-state functional magnetic resonance imaging (rs-fMRI) obtained from cognitively normal (CN), MCI, and PD patients with cognitive impairment (PD-CogImp). Using machine learning (linear and ensemble learning), we determined whether the identified functional patterns could classify abnormal function from normal function. Olfaction, as measured by objective testing, was found to be most strongly associated with diagnostic status, emphasizing the fundamental association of this primary sensory system with these conditions. Consistently lower functional connectivity was observed in the PD-CogImp cohort compared to the CN cohort among all identified brain regions. Differences were also found between PD-CogImp and MCI at the level of the orbitofrontal and cingulate cortices. MCI and CN subjects had different functional connectivity between the posterior orbitofrontal cortex and thalamus. Regardless of study group, males showed significantly higher connectivity than females in connections involving the orbitofrontal cortex. The logistic regression model trained using the top discriminatory features revealed that caudate was the most involved olfaction-related brain structure (accuracy = 0.88, Area under the Receiver operator characteristic curve of 0.90). In aggregate, our study demonstrates that resting functional connectivity among olfactory eloquent structures has potential value in better understanding the pathophysiology of several neurodegenerative diseases.

A novel olfactory sorting task

BACKGROUND

This study aimed to develop a simple self-administered screening tool for odor memory, which allowed users to self-test their olfactory function repeatedly even at home.

METHODS

One hundred and ten participants were recruited (30 men, age = 50.1 ± 9.9 years; 80 women, age = 47.1 ± 11.5 years); half of them were heathy volunteers, the other half were patients with olfactory dysfunction. Fifty-one healthy participants volunteered for a retest within an interval of a maximum of 14 days. Olfactory function was assessed using the extended Sniffin' Sticks test (SST) comprising tests for odor threshold, identification, and discrimination. All participants received the Novel Olfactory Sorting Task (NOST) which is based on the sorting of 12 matching pairs of odors involving olfactory and cognitive functions. After that, all participants rated questions related to their test performance and the practicability of the test.

RESULTS

Consistent with the previous literature, significant effects of age were found. Results showed an acceptable test-retest reliability and a satisfactory validity of the NOST. The NOST score not only had positive correlations with SST, but also was capable of differentiating severe hyposmia/anosmia from normosmia by the score of 5.5 (sensitivity of 76.2%, specificity of 77.6%).

CONCLUSION

The present study showed the good reliability, validity, and possible clinical usefulness of the NOST. As a self-performed screening test, it can be comprehended and conducted easily, which may provide a quick and simple approach to obtaining a global estimation of olfactory and cognitive functions.

Reduction in the olfactory ability in aging Mitf mutant mice without evidence of neurodegeneration

Age-related decline occurs in most brain structures and sensory systems. An illustrative case is olfaction. The olfactory bulb (OB) undergoes deterioration with age, resulting in reduced olfactory ability. A decline in olfaction is also associated with early symptoms of neurodegenerative diseases, including Alzheimer's disease (AD) and Parkinson's disease (PD). However, the underlying reasons are unclear. The microphthalmia-associated transcription factor (MITF) is expressed in the projection neurons (PNs) of the OB-the mitral and tufted (M/T) cells. Primary M/T cells from Mitf mutant mice show hyperactivity, potentially attributed to the reduced expression of a key potassium channel subunit, Kcnd3/Kv4.3. This influences intrinsic plasticity, an essential mechanism involving the non-synaptic regulation of neuronal activity. As neuronal hyperactivity often precedes neurodegenerative conditions, the current study aimed to determine whether the absence of Mitf causes degenerative effects during aging. Aged Mitf mutant mice showed reduced olfactory ability without inflammation. However, an increase in the expression of potassium channel subunit genes in the OBs of aged Mitf mi-vga9/mi-vga9 mice suggests that during aging, compensatory mechanisms lead to stabilization.

Aging is associated with a modality-specific decline in taste

Deficits in chemosensory processing are associated with healthy aging, as well as numerous neurodegenerative disorders, including Alzheimer's disease (AD). The fruit fly, Drosophila melanogaster, is a powerful model for studying chemosensation, aging, and aging-related pathologies, yet the effects of aging and neurodegeneration on taste function remain largely unexplored. Aging impaired response to sugars, but not medium-chain fatty acids that are sensed by a shared population of neurons. Selective expression of the human amyloid beta (Aβ) peptide phenocopied the effects of aging. Functional imaging of gustatory axon terminals revealed reduced response to sugar, but not fatty acids. Axonal innervation of the fly taste center was largely intact in aged flies; however, axonal innervation was reduced upon expression of Aβ. A comparison of transcript expression within the sugar-sensing taste neurons revealed age-related changes in 66 genes. Together, these findings suggest that different mechanisms underly taste deficits in aged and AD model flies.

A first-of-its-kind 3D biomimetic artificial mouth capable of reproducing the oral processing of soft foods

With a growing global population and ageing demographics, the food industry stands at a pivotal crossroads, necessitating bespoke solutions and groundbreaking innovations. In vitro experiments can help understanding food oral processing and formulating products meeting the specific needs of different populations. However, current in vitro models do not reproduce well human oral anatomy and tongue biomechanics, essential for assessing the behaviour of novel and texturized foods under physiologically relevant oral conditions. In response, we unveil a novel 3D biomimetic artificial mouth, showcasing a pneumatic multi-degree-of-freedom artificial tongue meticulously crafted to mirror the mechanical properties and wettability of the human tongue. This cutting-edge technology, featuring tongue surface papillae, is capable of performing lifelike movements. The comparison with in vivo data demonstrates that it accurately reproduces oral processing of three, vastly different, soft foods. Textural characteristics (firmness, adhesive and cohesive properties) and shear viscosities-measured at oral and oropharyngeal-relevant shear rates-of in vitro food boli closely mirrored those observed in vivo. This in vitro device presents unprecedented opportunities for studying the dynamics of food transformation in the mouth, to adapt texture towards food that can be swallowed with ease and to improve food palatability, accommodating specific health needs critical for older adults (e.g., reduced salivary secretion, tongue weakness or poor coordination).

Decline of olfactory function in Parkinson's disease: A ten-year longitudinal study

BackgroundOlfactory dysfunction is a prodromal sign of Parkinson's disease (PD) present in up to 90% of patients. However, it is unclear whether or not olfactory function worsens over the course of the disease.ObjectiveIn this study we examined whether the rate of decline of olfactory function in PD patients exceeds the expected age-related decline.MethodsOlfactory function was tested in 90 PD patients at baseline (age at baseline 58.3 years, 68.9% males) and an average 10 years later using the 40-item University of Pennsylvania Smell Identification Test (UPSIT). To screen for concomitant cognitive deficits as a potential confounder, the Mini-Mental State Examination (MMSE) was used.ResultsAt baseline, the mean UPSIT score was 22 points. Over the average 10-year follow-up period olfactory function decreased in 81.1% of PD patients, even in the youngest patients in whom no age-related decline was expected. The mean decrease was six UPSIT points (p < 0.001), which exceeds the expected age-related decline derived from a previous study. When excluding patients with an MMSE score below 24, reflecting cognitive deficits that might interfere with olfactory test performance, UPSIT score still decreased by almost 7 points over the follow-up period.ConclusionsOlfactory function in PD declines more rapidly with increasing disease duration than can be explained by aging or cognitive decline alone. As such, olfactory function appears to be a clinical marker of disease progression in PD that can be measured non-invasively and deserves consideration as part of multimodal phenotyping to monitor disease progression.

Factors associated with loss and recovery of smell and taste after COVID-19 infection

Objective

To identify predictors associated with loss and recovery of smell and taste after COVID-19 infection.

Methods

The Integrated Public Use Microdata Series (IPUMS) 2021 National Health Interview Series (NHIS) database was used to analyze factors associated with loss and recovery of smell and taste in respondents who had a previous COVID-19 infection. Significant variables from univariate analysis were included in a stepwise backward regression model to identify independent predictors.

Results

Of the 3844 individuals who answered yes to having contracted COVID-19, 51.1% and 48.9% reported losing smell and taste, respectively. 95.7% recovered smell and 97% recovered taste. Predictors associated with higher odds of reporting a loss of smell included younger age (odds ratio [OR] 0.98; 95% confidence interval [CI] 0.98-0.99), female sex (OR 1.38; CI 1.17-1.63), use of e-cigarettes (OR 1.59; CI 1.25-2.02), and Mexican ethnicity (OR 1.61; CI 1.22-2.11). Predictors of taste loss were younger age (OR 0.98; CI 0.98-0.99), female sex (OR 1.31; CI 1.08-1.58), and higher BMI (OR 1.02; CI 1.00-1.04). Female sex was associated with decreased odds of reporting a recovery of smell (OR 0.74; CI 0.59-0.92) and taste (OR 0.54; CI 0.42-0.69). Black/African American race (OR 1.44; CI 1.03-2.03) and non-Mexican Hispanic ethnicities (OR 1.55; CI 1.02-2.34) were associated with an increased likelihood of reporting the recovery of smell.

Conclusion

Various factors may be associated with the loss and recovery of smell and taste after COVID-19 infections. Clinicians may use this information to better counsel patients with these symptoms.

Level of evidence

4.

Odor identification and progression to dementia: The role of odor characteristics and set size

INTRODUCTION

We evaluated short versions of a 16-item odor identification (OID) test, with regard to their ability to identify individuals at high dementia risk.

METHODS

Participants from the population-based SNAC-K study (n = 2418) were followed across 12 years. We formed 13 abbreviated clusters based on the identifiability and perceptual characteristics of the Sniffin' Sticks Test (SST) items, and pre-existing test versions. Dementia hazard was estimated with Cox regressions.

RESULTS

Lower OID scores were associated with an increased dementia hazard across all odor clusters. Lower performance in the high identifiability cluster showed the strongest association with dementia (hazard ratio = 1.39, 95% confidence interval [1.28-1.51]). Moreover, the high-intensity odor cluster showed a stronger association with dementia than the low-intensity cluster (P = 0.02).

DISCUSSION

The findings suggest that the SST items differ with regard to their association with dementia and support using a reduced set size for clinical practice.

Highlights

Odor identification (OID) items differ in their association with future dementia.Reduced OID set sizes render hazard ratios comparable to larger set sizes.Identifiability and perceptual characteristics of odors should be considered when designing dementia screening instruments.

As a phenomenon: Ramadan fasting improves olfactory performance

Objective

The present study objectived to investigate the influence of Ramadan fasting (RF) on olfactory function.

Methods

Sixty-two participants were included in the current prospective study. The odor threshold and identification performances were determined by using the Connecticut Chemosensory Clinical Research Center (CCCRC) test initially (day 0) and on the first and last day (30th) of RF. Body weight (BW)s were measured initially and at the end of the study. The results were analyzed statistically.

Results

The average of baseline and last-day BWs were 78.38 ± 12.96 and 78.36 ± 12.39 kg, respectively. No significant difference was determined in terms of BWs (p = .932, p > .05). In the evaluation of CCCRC test outcomes, significant differences were observed in the scores of butanol thresholds (p = .0001), odor identification (p = .0001), food-related odors identification (p = .0001), and the number of normosmic individuals (p = .0001) at different times (p < .05). The thresholds scores (p = .0001, p = .0001), the identification scores (p = .0001, p = .0001), food-related odors identification scores (p = .0001, p = .0002), and the number of normomic individuals (p = .001, p = .001) detected on 30th day were significantly higher than on 0th and 1st days; respectively (p < .05). Additionally, the threshold scores (p = .0001), the identification scores (p = .003), food-related odors identification scores (p = .007), and the number of normosmic individuals (p = .018) detected on day 1 were significantly higher than on day 0 (p < .05).

Conclusion

The current study demonstrated that Ramadan fasting enhances the olfactory detection threshold and odor identification scores, significantly improving the identification of food-related odors. The results may indicate that Ramadan fasting improves olfactory performance.

Level of evidence

Level II.

The interplay between tauopathy and aging through interruption of UPR/Nrf2/autophagy crosstalk in the Alzheimer's disease transgenic experimental models

PURPOSE

Alzheimer's disease (AD) is the most common form of tauopathy that usually occursduring aging and unfolded protein response (UPR), oxidative stress and autophagy play a crucialrole in tauopathy-induced neurotoxicity. The aim of this study was to investigate the effects oftauopathy on normal brain aging in a Drosophila model of AD.

METHOD

We investigated the interplay between aging (10, 20, 30, and 40 days) and human tauR406W (htau)-induced cell stress in transgenic fruit flies.

RESULTS

Tauopathy caused significant defects in eye morphology, a decrease in motor function and olfactory memory performance (after 20 days), and an increase in ethanol sensitivity (after 30 days). Our results showed a significant increase in UPR (GRP78 and ATF4), redox signalling (p-Nrf2, total GSH, total SH, lipid peroxidation, and antioxidant activity), and regulatory associated protein of mTOR complex 1 (p-Raptor) activity in the control group after 40 days, while the tauopathy model flies showed an advanced increase in the above markers at 20 days of age. Interestingly, only the control flies showed reduced autophagy by a significant decrease in the autophagosome formation protein (dATG1)/p-Raptor ratio at 40 days of age. Our results were also confirmed by bioinformatic analysis of microarray data from tauPS19 transgenic mice (3, 6, 9, and 12 months), in which tauopathy increased expression of heme oxygenase 1, and glutamate-cysteine ligase catalytic subunit and promote aging in transgenic animals.

CONCLUSIONS

Overall, we suggest that the neuropathological effects of tau aggregates may be accelerated brain aging, where redox signaling and autophagy efficacy play an important role.

Effect of physical activity on olfaction acuity: A systematic review

Olfaction acuity, which includes detection thresholds, discrimination and identification, appears to decline with age, obesity, and various neurological disorders. Knowing that smell influences energy intake, there is a growing interest in protecting this sense. Physical activity could be a key intervention to counteract the loss of olfaction. This systematic review aims to explore the literature on the effect of physical activity on olfaction acuity. The search strategy consisted of using index terms and keywords in MEDLINE, EMBASE, EBM Reviews - Cochrane Central Register of Controlled Trials, CINAHL, SPORTDiscus, and Web of Science search engine. Data from 17 trials involving 10,861 participants showed that physical activity improved olfaction thresholds, discrimination, identification and perceived intensity. Regular practice of physical activity seemed to have better effects on olfaction components than acute exercise. Although this review has clarified the evidence on the effects of physical activity on olfaction, better methodological consistency is needed.

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

PURPOSE

Study the efficacy of olfactory training in smell recovery.

METHODS

An 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.

RESULTS

Final 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.

CONCLUSION

Olfactory training was found to have a positive and significant effect on rehabilitating the olfactory function.

A Pilot Study of the Computerized Brief Smell Identification Test

Objectives: A self-administered Computerized Brief Smell Identification Test (cB-SIT) was developed recently to perform the olfactory identification test under computer control. The aim of this study was to evaluate the clinical applicability of the cB-SIT as compared with the traditional Brief Smell Identification Test (B-SIT). Methods: Sixty healthy volunteers with self-reported normal olfactory function, 30 hyposmic patients, and 30 anosmic patients were enrolled from June 2023 to May 2024. All enrolled participants received both B-SIT and cB-SIT in a random order to measure their odor identification ability. Thirty healthy volunteers took the second B-SIT and cB-SIT at least one week later. Results: The score was significantly different in both B-SIT and cB-SIT among healthy volunteers, hyposmic, and anosmic patients. The correct answer rate was significantly different in 10 items of the B-SIT and in 7 items of the cB-SIT among the three groups, but the post hoc test showed significant differences in correct answer rates between healthy volunteers and hyposmic patients in 7 items of both the B-SIT and cB-SIT. Test-retest results showed the score of the second B-SIT test was significantly higher than that of the first test, but the scores of the two tests of the cB-SIT were not significantly different. In the B-SIT, the lemon odorant had a higher correct answer rate in the second test than in the first test, but in the cB-SIT, the correct answer rate was not significantly different between the first and second tests in all 12 items. Conclusions: Our findings demonstrate that the cB-SIT was similar to the B-SIT and can be administered in the diagnosis of patients with olfactory dysfunction.

COVID-19 is associated with changes in brain function and structure: A multimodal meta-analysis of neuroimaging studies

The actual role of coronavirus disease 2019 (COVID-19) in brain damage has been increasingly reported, necessitating a meta-analysis to collate and summarize the inconsistent findings from functional imaging and voxel-based morphometry (VBM) studies. A comprehensive voxel-wise meta-analysis of the whole brain was conducted to identify alterations in functional activity and gray matter volume (GMV) between COVID-19 patients and healthy controls (HCs) by using Seed-based d Mapping software. We included 15 functional imaging studies (484 patients with COVID-19, 534 HCs) and 9 VBM studies (449 patients with COVID-19, 388 HCs) in the analysis. Overall, patients with COVID-19 exhibited decreased functional activity in the right superior temporal gyrus (STG) (extending to the right middle and inferior temporal gyrus, insula, and temporal pole [TP]), left insula, right orbitofrontal cortex (OFC) (extending to the right olfactory cortex), and left cerebellum compared to HCs. For VBM, patients with COVID-19, relative to HCs, showed decreased GMV in the bilateral anterior cingulate cortex/medial prefrontal cortex (extending to the bilateral OFC), and left cerebellum, and increased GMV in the bilateral amygdala (extending to the bilateral hippocampus, STG, TP, MTG, and right striatum). Moreover, overlapping analysis revealed that patients with COVID-19 exhibited both decreased functional activity and increased GMV in the right TP (extending to the right STG). The multimodal meta-analysis suggests that brain changes of function and structure in the temporal lobe, OFC and cerebellum, and functional or structural alterations in the insula and the limbic system in COVID-19. These findings contribute to a better understanding of the pathophysiology of brain alterations in COVID-19. SIGNIFICANCE STATEMENT: This first large-scale multimodal meta-analysis collates existing neuroimaging studies and provides voxel-wise functional and structural whole-brain abnormalities in COVID-19. Findings of this meta-analysis provide valuable insights into the dynamic brain changes (from infection to recovery) and offer further explanations for the pathophysiological basis of brain alterations in COVID-19.

Prevalence and factors associated with olfactory impairment among patients with acne treated with oral isotretinoin: a cross-sectional study

OBJECTIVE

This study aimed to investigate the prevalence and factors associated with olfactory dysfunction in individuals exposed to Isotretinoin (ISO) for the treatment of acne, using the University of Pennsylvania Smell Identification Test (UPSIT®).

METHODS

This cross-sectional study enrolled age and sex-matched patients with acne who were current users of oral ISO and unexposed controls without olfactory complaints. UPSIT® and a validated questionnaire (Nasal Obstruction Symptom Evaluation) were administered to evaluate nasal obstruction in patients exposed to ISO.

RESULTS

A total of seventy patients were recruited, with 35 in the exposed group and 35 in the unexposed group, consisting of 18 males and 17 females in each group, aged from 17 to 47 years. The prevalence of olfactory dysfunction was higher in the exposed group compared to the non-exposed group (62.9% vs. 17.1%), yielding a Prevalence Ratio (PR) of 3.7 (95% CI 1.9-7.1). However, no participants were categorized as anosmia or severe hyposmia and the majority of dysfunction was mild hyposmia compared to moderate hyposmia (51.5% vs. 11.4%). Among the exposed individuals, gasoline, orange, coffee, and wood exhibited the highest rates of identification errors (≥54%). Olfactory function demonstrated a negative correlation with treatment duration (p = 0.01), cumulative dose (p = 0.02), and nasal obstruction (p = 0.02).

CONCLUSIONS

Olfactory dysfunction was more prevalent among ISO users, despite the patients being unaware of the disorder. Olfactory changes were correlated with treatment duration, cumulative dose, and nasal obstruction.

LEVEL OF EVIDENCE

Level 4.

Olfactory Impairment and Frailty: A Systematic Review and Meta-Analysis

Importance

Olfactory impairment (OI) and frailty are prevalent conditions associated with aging, but studies investigating their association with each other have been discordant.

Objective

To summarize current evidence surrounding the association between OI and frailty.

Data Sources

PubMed, Embase, Cochrane Library, SCOPUS, and CINAHL from inception to November 28, 2023.

Study Selection

This study included observational studies investigating the association between objectively or subjectively assessed OI and objectively evaluated frailty among adults.

Data Extraction and Synthesis

Two independent authors extracted data into a structured template. Maximally adjusted estimates were pooled using a random-effects model, and statistical heterogeneity was evaluated using I2 values. Additional prespecified subgroup and sensitivity analyses were performed. This study used the Newcastle-Ottawa Scale for bias assessment and the Grading of Recommendations Assessment, Development and Evaluation framework for overall evidence quality evaluation.

Main Outcomes and Measures

The primary outcome was the cross-sectional association between OI and frailty, for which the odds of frailty were compared between participants with and without OI. The secondary outcome was the cross-sectional association between frailty and OI, for which the odds of OI were compared between participants with and without frailty.

Results

This study included 10 studies with 10 624 patients (52.9% female; mean [SD] age, 62.9 [9.6] years). The Newcastle-Ottawa Scale score of studies ranged from low to moderate. Grading of Recommendations Assessment, Development and Evaluation scores ranged from low to moderate. OI was associated with a 2.32-fold (odds ratio [OR], 2.32; 95% CI, 1.63-3.31; I2 = 0%) greater odds of frailty compared with individuals with healthy olfactory function. The odds of OI was progressively greater with categorical frailty status, with a 1.55-fold (OR, 1.55; 95% CI, 1.32-1.82; I2 = 0%), 2.28-fold (OR, 2.28; 95% CI, 1.96-2.65; I2 = 0%), and 4.67-fold (OR, 4.67; 95% CI, 2.77-7.86; I2 = 0%) increase in odds for individuals with prefrailty, frailty, and the most frailty, respectively, compared with robust individuals. The results demonstrated stability in subgroup analyses (geographical continent of study, objective vs subjective olfactory assessment) and sensitivity tests.

Conclusions and Relevance

The results of this systematic review and meta-analysis suggest that there is an association between OI and frailty, with an increase in the odds of OI with worsening categorical frailty status among individuals with prefrailty, frailty, and the most frailty. OI may be a potential biomarker for frailty. Future studies could delve into whether OI may be a modifiable risk factor for frailty.

The role of olfactory dysfunction in mild cognitive impairment and Alzheimer's disease: A meta-analysis

PURPOSE

This comprehensive meta-analysis investigates the association between olfactory deficits in mild cognitive impairment (MCI) and Alzheimer's disease (AD).

METHODS

A thorough search across databases identified articles analyzing olfactory status in MCI or AD patients. Methodological quality assessment followed PRISMA guidelines. Hedges' g effect size statistic computed standard mean differences and 95% confidence intervals. Moderator analysis was conducted.

RESULTS

Among the included studies (65 for MCI and 61 for AD), odor identification exhibited larger effect sizes compared to odor threshold and discrimination, in both MCI and AD samples. Moderate effect size is found in OI scores in MCI (k = 65, SE = 0.078, CI 95% = [-1.151, -0.844]). Furthermore, compared to MCI, AD had moderate to large heterogeneous effects in olfactory identification (k = 61, g = -2.062, SE = 0.125, CI 95% = [-2.308, -1.816]). Global cognitive status is positively related to olfactory identification impairment in both MCI (k = 57, Z = 2.74, p = 0.006) and AD (k = 53, Z = 5.03, p < 0.0001) samples.

CONCLUSION

Olfactory impairments exhibit a notable and substantial presence in MCI. Among these impairments, odor identification experiences the greatest decline in MCI, mirroring the primary sensory deficit observed in AD. Consequently, the incorporation of a straightforward odor identification test is advisable in the evaluation of individuals vulnerable to the onset of AD, offering a practical screening tool for early detection.

Olfactory Impairment and the Risk of Major Adverse Cardiovascular Outcomes in Older Adults

BACKGROUND

Olfactory impairment is common in older adults and may be associated with adverse cardiovascular health; however, empirical evidence is sparse. We examined olfaction in relation to the risk of coronary heart disease (CHD), stroke, and congestive heart failure (CHF).

METHODS AND RESULTS

This study included 2537 older adults (aged 75.6±2.8 years) from the Health ABC (Health, Aging, and Body Composition) study with olfaction assessed by the 12-item Brief Smell Identification Test in 1999 to 2000, defined as poor (score ≤8), moderate (9-10), or good (11-12). The outcomes were incident CHD, stroke, and CHF. During up to a 12-year follow-up, 353 incident CHD, 258 stroke, and 477 CHF events were identified. Olfaction was statistically significantly associated with incident CHF, but not with CHD or stroke. After adjusting for demographics, risk factors, and biomarkers of CHF, the cause-specific hazard ratio (HR) of CHF was 1.32 (95% CI, 1.05-1.66) for moderate and 1.28 (95% CI, 1.01-1.64) for poor olfaction. These associations were robust in preplanned subgroup analyses by age, sex, race, and prevalent CHD/stroke. While the subgroup results were not statistically significantly different, the association of olfaction with CHF appeared to be evident among participants who reported very good to excellent health (HR, 1.47 [95% CI, 1.01-2.14] for moderate; and 1.76 [95% CI, 1.20-2.58] for poor olfaction), but not among those with fair to poor self-reported health (HR, 1.04 [95% CI, 0.64-1.70] for moderate; and 0.92 [95% CI, 0.58-1.47] for poor olfaction).

CONCLUSIONS

In community-dwelling older adults, a single olfaction test was associated with a long-term risk for incident CHF, particularly among those reporting very good to excellent health.

Correlations among serum alpha-(1,6)-fucosyltransferase and early symptoms associated with Parkinson's disease: A cross-sectional retrospective study

Alpha-(1,6)-fucosyltransferase (FUT8) has been found to play a role in modulating the central immune system and inflammatory responses. Limited studies have assessed the correlations between serum FUT8 levels and various non-motor symptoms associated with early Parkinson's disease (PD). Therefore, our research aims to investigate the associations between serum FUT8 levels and symptoms such as smell dysfunction, sleep duration, sleep problems, and MMSE scores in PD patients. FUT8 and neurofilament light chain (NfL) levels were measured using enzyme-linked immunosorbent assays (ELISA). We analyzed the correlations between serum FUT8 levels, NfL, and early symptoms of PD using Spearman's correlation, multiple linear regression, and logistic regression models. The expression of FUT8 in CSF samples from PD patients was significantly upregulated, with its protein levels in CSF being positively associated with serum levels. Furthermore, there were significant positive associations between serum FUT8 levels with NfL levels, smell dysfunction, short sleep duration, and long sleep duration. However, a significant inverse relationship was observed between FUT8 levels and MMSE scores. Additionally, we explored gender and age differences in the correlations of FUT8 levels and early symptoms in patients. This study reveals that increased FUT8 levels are positively correlated with a higher risk of early PD-associated symptoms. These findings suggest that serum FUT8 could serve as a promising biomarker for the early detection of PD.

Tau propagation in the brain olfactory circuits is associated with smell perception changes in aging

The direct access of olfactory afferents to memory-related cortical systems has inspired theories about the role of the olfactory pathways in the development of cortical neurodegeneration in Alzheimer's disease (AD). In this study, we used baseline olfactory identification measures with longitudinal flortaucipir and PiB PET, diffusion MRI of 89 cognitively normal older adults (73.82 ± 8.44 years; 56% females), and a transcriptomic data atlas to investigate the spatiotemporal spreading and genetic vulnerabilities of AD-related pathology aggregates in the olfactory system. We find that odor identification deficits are predominantly associated with tau accumulation in key areas of the olfactory pathway, with a particularly strong predictive power for longitudinal tau progression. We observe that tau spreads from the medial temporal lobe structures toward the olfactory system, not the reverse. Moreover, we observed a genetic background of odor perception-related genes that might confer vulnerability to tau accumulation along the olfactory system.

The association between parameters of physical activity and olfactory function-the importance of frequency and moderate intensity

Introduction

Overall physical activity (PA) has been linked to decreased olfactory dysfunction and could improve olfactory function. Additionally, decreased olfactory function can contribute to reduced overall PA levels, given its association with neurodegenerative disorders. This study aims to examine the relationship between specific PA parameters (duration, frequency, intensity) and olfactory function in adults.

Methods

A total of 3,527 participants from the National Health and Nutrition Examination Survey (NHANES) 2013-2014 underwent assessments for weekly PA duration, frequency, and intensity, alongside a smell test (including odors such as chocolate, strawberry, grape, onion, smoke, natural gas, leather, and soap). Correlation analyses and binary logistic regressions using SPSS were used to evaluate associations.

Results

The total smell score exhibited small yet significant positive correlations with the duration, frequency, and volume of moderate PA (correlation coefficients ranging between 0.05 and 0.08; all p ≤ 0.05) and frequency of vigorous PA (correlation coefficient of 0.05; p < 0.05). For moderate PA, the duration, frequency, and volume were significantly and positively associated with the ability to correctly detect the smell of grapes while the frequency was significantly and positively associated with the ability to identify smoke and leather odors (odds ratios ranging from 1.01 to 1.07; p < 0.05). For vigorous PA, the frequency of PA was positively associated with the detection of grape smell (odds ratio of 1.05; p < 0.05).

Conclusion

Some parameters of an active lifestyle are associated with improved odds of accurately identifying odors by up to 7.4%. Moderate PA duration, frequency, and volume were linked to better olfactory scores, while high-intensity PA had limited associations.

Older adults' acceptability of and preferences for food-based protein fortification in the UK, France and Norway

Research suggests that as we age, protein intake, recognised as vital for combating negative health outcomes, consistently falls below recommendations in older adults. Decreased food intake, combined with age-related eating complications is a major determinant of this protein undernutrition. If nutritional interventions are to be effective and sustainable, they must enable eating pleasure, cater for personal preferences and be adaptable to different eating patterns. As such, we aimed to identify successful strategies for at-home protein-fortification to empower older adults to take a personalised approach to their nutrition, without requiring a large behavioural change. To explore healthy older adults' (age 70+) acceptability and preferences for at-home protein fortification, European project Fortiphy led discussions with older adults (n = 37) and caregivers of older adults (n = 15) to develop high-protein recipes, which were then utilised in a home-use trial with healthy older adults (n = 158). Each fortified recipe was paired with a questionnaire to rate the ease of preparation and liking, and an end-of-study questionnaire was provided to capture overall opinions and preferences. The uniqueness of this study is that the protein fortified recipes were prepared and tested by older adults themselves, in their own homes. Findings showed that older adults were unaware of the importance of protein in ageing and did not have a desire to fortify their foods at present. Yet, they were positive regarding the concept and highlighted the importance of taste, familiar ingredients, and preferred preparation methods. Cultural preferences across countries were identified as having the most influence on the liking of fortified meals. This study also indicated a need for increased awareness of protein requirements to influence the motivation to use fortification.

Correlations between Gustatory, Olfactory, Cognitive Function, and Age in Healthy Women

Aging is a progressive physiological degeneration associated with a decline in chemosensory processes and cognitive abilities and a reduction in synaptic plasticity. The biological bases of ageing are still not completely understood, and many theories have been proposed. This study aimed to evaluate the occurrence of age-related changes affecting the chemosensory function (gustatory and olfactory) and general cognitive abilities and their potential associations in women. To this aim, 319 women (the age ranging from 18 to 92 years) were recruited and divided into four different age groups: 18-34 years, 35-49 years, 50-64 years, and ≥65 years. Our results confirmed that in women, gustatory, olfactory, and cognitive functions decline, though in a different manner during aging. Olfactory and cognitive function showed a slight decline along the first three age classes, with a dramatic decrease after age 65 years, while gustatory function decreased more gradually. Olfactory and gustatory deficits may have a high degree of predictivity for general cognitive function as well as for specific cognitive subdomains such as visuospatial/executive abilities, language, memory, and attention. Our study highlighted the importance of using chemosensory assessments for the early diagnosis of cognitive decline and for the development of appropriate personalized risk prevention strategies.

Success in the Natural Detection Task is influenced by only a few factors generally believed to affect dogs' olfactory performance

Research into dogs' olfactory ability is growing rapidly. However, generalising based on scientific results is challenging, because research has been typically conducted on a few specially trained subjects of a few breeds tested in different environmental conditions. We investigated the effects of temperature and humidity (outdoors), age, test location, sex, neutering status, and repeated testing (outdoors and indoors) on the olfactory performance of untrained family dogs (N = 411) of various breeds. We employed the Natural Detection Task with three difficulty levels, from which we derived two performance metrics: Top Level and Success Score. Temperature (0-25 °C) and humidity (18-90%) did not affect olfactory performance. Young adult dogs surpassed other age groups in reaching the Top Level. Sex and neutering status showed no discernible influence on Top Level and Success Score. Dogs performed better in both metrics when tested indoors compared to outdoors. In the test-retest procedure no significant learning effect was observed. We confirmed on untrained companion dogs that olfactory performance declines with age and rejected some factors that have been previously hypothesised to significantly affect dogs' olfactory success. The influence of the testing environment was notable, emphasising the need to consider various factors in understanding dogs' olfactory capabilities.

Sensational Dreams: The Prevalence of Sensory Experiences in Dreaming

Dreaming, a widely researched aspect of sleep, often mirrors waking-life experiences. Despite the prevalence of sensory perception during wakefulness, sensory experiences in dreams remain relatively unexplored. Free recall dream reports, where individuals describe their dreams freely, may not fully capture sensory dream experiences. In this study, we developed a dream diary with direct questions about sensory dream experiences. Participants reported sensory experiences in their dreams upon awakening, over multiple days, in a home-based setting (n = 3476 diaries). Our findings show that vision was the most common sensory dream experience, followed by audition and touch. Olfaction and gustation were reported at equally low rates. Multisensory dreams were far more prevalent than unisensory dreams. Additionally, the prevalence of sensory dream experiences varied across emotionally positive and negative dreams. A positive relationship was found between on the one hand sensory richness and, on the other emotional intensity of dreams and clarity of dream recall, for both positive and negative dreams. These results underscore the variety of dream experiences and suggest a link between sensory richness, emotional content and dream recall clarity. Systematic registration of sensory dream experiences offers valuable insights into dream manifestation, aiding the understanding of sleep-related memory consolidation and other aspects of sleep-related information processing.

Body odours as putative chemosignals in the father-child relationship: New insights on paternal olfactory kin recognition and preference from infancy to adolescence

Children's body odours are effective chemical cues in the parent-child relationship. Mothers can recognize the odour of their child and prefer this odour over that of unfamiliar children. This effect is mediated by genetic similarity and developmental stage and is therefore suited to promote parental care at pre-pubertal stage, while facilitating incest avoidance at (post-)pubertal stage. The present study tested whether similar mechanisms apply to fathers. Therefore n = 56 fathers evaluated body odour samples of their own and of unfamiliar children in varying genetic and developmental stages. Genetic status was determined by human leucocyte antigen (HLA) profiling, developmental status by standardized assessment of pubertal status and steroid hormone concentration (estradiol, testosterone). Similar to mothers, fathers identified their own child's body odour above chance and preferred that odour. The paternal preference did not relate to HLA similarity but decreased with increasing age of the child. The decline was associated with higher pubertal stages in daughters only, which supports the hypothesis of odour-mediated incest prevention in opposite-sex parent-child dyads.

Age-related differences in perception and coding of attractive odorants in mice

Hedonic perception deeply changes with aging, significantly impacting health and quality of life in elderly. In young adult mice, an odor hedonic signature is represented along the antero-posterior axis of olfactory bulb, and transferred to the olfactory tubercle and ventral tegmental area, promoting approach behavior. Here, we show that while the perception of unattractive odorants was unchanged in older mice (22 months), the appreciation of some but not all attractive odorants declined. Neural activity in the olfactory bulb and tubercle of older mice was consistently altered when attraction to pleasant odorants was impaired while maintained when the odorants kept their attractivity. Finally, in a self-stimulation paradigm, optogenetic stimulation of the olfactory bulb remained rewarding in older mice even without ventral tegmental area's response to the stimulation. Aging degrades behavioral and neural responses to some pleasant odorants but rewarding properties of olfactory bulb stimulation persisted, providing new insights into developing novel olfactory training strategies to elicit motivation even when the dopaminergic system is altered as observed in normal and/or neurodegenerative aging.

Normative Data for the 12-Item Sniffin' Sticks Odor Identification Test in Older Adults

OBJECTIVE

Quantitative olfactory assessment has demonstrated clinical utility for the evaluation of a range of neurologic, psychiatric, and sinonasal conditions. Here, we provide age, sex, race, and education-specific normative data for the 12-item Sniffin Sticks Odor Identification Test (SSOIT-12) in older Black and White U.S. adults without preclinical or clinical dementia or sinonasal disease.

METHOD

A sample of 2,224 Atherosclerosis Risk in Communities study participants aged 66-89 years were included. A normative regression equation was developed using a linear model for the association of age, sex, race, and education with odor identification score. Regression-based normative mean scores and percentiles were generated by age, sex, race, and education groups.

RESULTS

Participants (mean age = 74 years, 59% women, 20% Black, 48% > high school education) had a mean SSOIT-12 score of 9.8. Age, sex, race, and education were all associated with odor identification performance (all ps < .05). A linear regression model for the predicted SSOIT-12 score was developed for use with an individual's actual SSOIT-12 score in order to calculate the Z-score and corresponding percentile for a specific age, sex, race, and education group. Data are also reported in tabular format.

CONCLUSIONS

Our study provides SSOIT-12 normative data obtained from a large population of White and Black older adults without preclinical or clinical dementia or sinonasal disease living in the USA. These findings can aid clinicians in assessing the degree of olfactory loss, establishing concordance with a person's perception of olfactory difficulties and quantitatively monitoring changes in olfactory performance over time.

A Pilot Study on a Possible Mechanism behind Olfactory Dysfunction in Parkinson's Disease: The Association of TAAR1 Downregulation with Neuronal Loss and Inflammation along Olfactory Pathway

Parkinson's disease (PD) is characterized not only by motor symptoms but also by non-motor dysfunctions, such as olfactory impairment; the cause is not fully understood. Our study suggests that neuronal loss and inflammation in brain regions along the olfactory pathway, such as the olfactory bulb (OB) and the piriform cortex (PC), may contribute to olfactory dysfunction in PD mice, which might be related to the downregulation of the trace amine-associated receptor 1 (TAAR1) in these areas. In the striatum, although only a decrease in mRNA level, but not in protein level, of TAAR1 was detected, bioinformatic analyses substantiated its correlation with PD. Moreover, we discovered that neuronal death and inflammation in the OB and the PC in PD mice might be regulated by TAAR through the Bcl-2/caspase3 pathway. This manifested as a decrease of anti-apoptotic protein Bcl-2 and an increase of the pro-apoptotic protein cleaved caspase3, or through regulating astrocytes activity, manifested as the increase of TAAR1 in astrocytes, which might lead to the decreased clearance of glutamate and consequent neurotoxicity. In summary, we have identified a possible mechanism to elucidate the olfactory dysfunction in PD, positing neuronal damage and inflammation due to apoptosis and astrocyte activity along the olfactory pathway in conjunction with the downregulation of TAAR1.