Olfactory discrimination predicts cognitive decline among community-dwelling older adults

Multiple Early Biomarkers to Predict Cognitive Decline in Dementia-Free Older Adults

INTRODUCTION

Baseline olfactory impairment, poor performance on cognitive test, and medial temporal lobe atrophy are considered biomarkers for predicting future cognitive decline in dementia-free older adults. However, the combined effect of these predictors has not been fully investigated.

METHODS

A group of 110 participants without dementia were continuously recruited into this study, and underwent olfactory, cognitive tests and MRI scanning at baseline and 5-year follow-up. Olfactory function was assessed using the University of Pennsylvania Smell Identification Test (UPSIT). Participants were divided into the cognitive decliners and non-decliners.

RESULTS

Among 87 participants who completed the 5-year follow-up, cognitive decline was present in 32 cases and 55 remained stable. Compared with non-decliners, cognitive decliners presented lower scores on both the UPSIT and the Montreal Cognitive Assessment (MoCA), and smaller hippocampal volume at baseline (all P < .001). The logistic regression analysis revealed that lower scores on UPSIT and MoCA, and smaller hippocampal volume were strongly associated with subsequent cognitive decline, respectively (all P < .001). For the prediction of cognitive decline, lower score on UPSIT performed the sensitivity of 63.6% and specificity of 81.2%, lower score on MoCA with the sensitivity of 74.5% and specificity of 65.6%, smaller hippocampal volume with the sensitivity of 70.9% and specificity of 78.1%, respectively. Combining three predictors resulted in the sensitivity of 83.6% and specificity of 93.7%.

CONCLUSIONS

The combination of olfactory test, cognitive test with structural MRI may enhance the predictive ability for future cognitive decline for dementia-free older adults.

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.

AROMHA Brain Health Test: A Remote Olfactory Assessment as a Screen for Cognitive Impairment

Cost-effective, noninvasive screening methods for preclinical Alzheimer's disease (AD) and other neurocognitive disorders remain an unmet need. The olfactory neural circuits develop AD pathological changes prior to symptom onset. To probe these vulnerable circuits, we developed the digital remote AROMHA Brain Health Test (ABHT), an at-home odor identification, discrimination, memory, and intensity assessment. The ABHT was self-administered among cognitively normal (CN) English and Spanish speakers (n=127), participants with subjective cognitive complaints (SCC; n=34), and mild cognitive impairment (MCI; n=19). Self-administered tests took place remotely at home under unobserved (among interested CN participants) and observed modalities (CN, SCC, and MCI), as well as in-person with a research assistant present (CN, SCC, and MCI). Olfactory performance was similar across observed and unobserved remote self-administration and between English and Spanish speakers. Odor memory, identification, and discrimination scores decreased with age, and olfactory identification and discrimination were lower in the MCI group compared to CN and SCC groups, independent of age, sex, and education. The ABHT revealed age-related olfactory decline, and discriminated CN older adults from those with cognitive impairment. Replication of our results in other populations would support the use of the ABHT to identify and monitor individuals at risk for developing dementia.

Small effects of olfactory identification and discrimination on global cognitive and executive performance over 1 year in aging people without a history of age-related cognitive impairment

Olfactory and cognitive performance share neural correlates profoundly affected by physiological aging. However, whether odor identification and discrimination scores predict global cognitive status and executive function in healthy older people with intact cognition is unclear. Therefore, in the present study, we set out to elucidate these links in a convenience sample of 204 independently living, cognitively intact healthy Czech adults aged 77.4 ± 8.7 (61-97 years) over two waves of data collection (one-year interval). We used the Czech versions of the Montreal Cognitive Assessment (MoCA) to evaluate global cognition, and the Prague Stroop Test (PST), Trail Making Test (TMT), and several verbal fluency (VF) tests to assess executive function. As a subsidiary aim, we aimed to examine the contribution of olfactory performance towards achieving a MoCA score above vs. below the published cut-off value. We found that the MoCA scores exhibited moderate associations with both odor identification and discrimination. Furthermore, odor identification significantly predicted PST C and C/D scores. Odor discrimination significantly predicted PST C/D, TMT B/A, and standardized composite VF scores. Our findings demonstrate that olfaction, on the one hand, and global cognition and executive function, on the other, are related even in healthy older people.

Impairment of olfactory identification ability in ultra-high risk for psychosis and drug-naïve first episode psychosis

OBJECTIVE

Patients with psychotic diseases have been reported to exhibit abnormalities in their olfactory discrimination. These alterations have also been identified in people at high genetic or clinical risk for psychosis, suggesting olfactory discrimination dysfunction may be a potential risk factor for developing psychosis. Thus, the purpose of our study is to explore the difference in olfactory discrimination ability in the prosal stage and early stage of psychosis and to explore the potential risk factor of developed psychosis.

METHODS

We compared olfactory identification and cognitive function in 89 ultra-high-risk (UHR) individuals, 103 individuals with Drug-naïve first-episode schizophrenia (FES), 81 genetic high-risk (GHR) individuals, and 97 healthy controls (HC). Additionally, we compared olfactory identification and cognitive function between two groups; UHR individuals who later transitioned to psychosis (UHR-T; n = 33) and those who did not transition (UHR-NT; n = 42)). Furthermore, we analyzed the correlations between olfactory discrimination ability and cognitive function and symptoms and compared the olfactory function between men and women.

RESULTS

Patients with first-episode schizophrenia (FES) and those at ultra-high risk (UHR) for psychosis exhibited more significant deficits in olfactory identification than healthy controls (HC), while no differences in olfactory identification dysfunction were observed between the genetic high risk (GHR) and HC groups. Notably, individuals in the UHR group who later developed psyhchosis displayed a steeper marked decline in their baseline olfactory identification ability than that of those in the UHR group who did not develop psychosis. Cognitive dysfunction is widely observed in both the FES and UHR groups, with a distinct correlation identified between olfactory discrimination function and cognitive performance. Finally, overall, women exhibit significantly superior olfactory function than men.

CONCLUSION

In conclusion, these findings suggest that impairment of olfactory identification exists in the early stage of psychosis. Olfactory identification dysfunction may therefore be a potential marker of predicting the transition to schizophrenia.

Exploring symptom clusters in mild cognitive impairment and dementia with the NIH Toolbox

OBJECTIVE

Symptom clustering research provides a unique opportunity for understanding complex medical conditions. The objective of this study was to apply a variable-centered analytic approach to understand how symptoms may cluster together, within and across domains of functioning in mild cognitive impairment (MCI) and dementia, to better understand these conditions and potential etiological, prevention, and intervention considerations.

METHOD

Cognitive, motor, sensory, emotional, and social measures from the NIH Toolbox were analyzed using exploratory factor analysis (EFA) from a dataset of 165 individuals with a research diagnosis of either amnestic MCI or dementia of the Alzheimer's type.

RESULTS

The six-factor EFA solution described here primarily replicated the intended structure of the NIH Toolbox with a few deviations, notably sensory and motor scores loading onto factors with measures of cognition, emotional, and social health. These findings suggest the presence of cross-domain symptom clusters in these populations. In particular, negative affect, stress, loneliness, and pain formed one unique symptom cluster that bridged the NIH Toolbox domains of physical, social, and emotional health. Olfaction and dexterity formed a second unique cluster with measures of executive functioning, working memory, episodic memory, and processing speed. A third novel cluster was detected for mobility, strength, and vision, which was considered to reflect a physical functioning factor. Somewhat unexpectedly, the hearing test included did not load strongly onto any factor.

CONCLUSION

This research presents a preliminary effort to detect symptom clusters in amnestic MCI and dementia using an existing dataset of outcome measures from the NIH Toolbox.

Valid olfactory impairment tests can help identify mild cognitive impairment: an updated meta-analysis

Background

Olfactory testing is emerging as a potentially effective screening method for identifying mild cognitive impairment in the elderly population.

Objective

Olfactory impairment is comorbid with mild cognitive impairment (MCI) in older adults but is not well-documented in subdomains of either olfactory or subtypes of cognitive impairments in older adults. This meta-analysis was aimed at synthesizing the differentiated relationships with updated studies.

Methods

A systematic search was conducted in seven databases from their availability to April 2023. A total of 38 publications were included, including 3,828 MCI patients and 8,160 healthy older adults. Two investigators independently performed the literature review, quality assessment, and data extraction. The meta-analyses were conducted with Stata to estimate the average effects and causes of the heterogeneity.

Results

Compared to normal adults, MCI patients had severe impairments in olfactory function and severe deficits in specific domains of odor identification and discrimination. Olfactory impairment was more severe in patients with amnestic mild cognitive impairment than in patients with non-amnestic MCI. Diverse test instruments of olfactory function caused large heterogeneity in effect sizes.

Conclusion

Valid olfactory tests can be complementary tools for accurate screening of MCI in older adults.

Pathological features and molecular signatures of early olfactory dysfunction in 3xTg-AD model mice

BACKGROUND

Olfactory dysfunction is known to be an early manifestation of Alzheimer's disease (AD). However, the underlying mechanism, particularly the specific molecular events that occur during the early stages of olfactory disorders, remains unclear.

METHODS

In this study, we utilized transcriptomic sequencing, bioinformatics analysis, and biochemical detection to investigate the specific pathological and molecular characteristics of the olfactory bulb (OB) in 4-month-old male triple transgenic 3xTg-AD mice (PS1M146V/APPSwe/TauP301L).

RESULTS

Initially, during the early stages of olfactory impairment, no significant learning and memory deficits were observed. Correspondingly, we observed significant accumulation of amyloid-beta (Aβ) and Tau pathology specifically in the OB, but not in the hippocampus. In addition, significant axonal morphological defects were detected in the olfactory bulb, cortex, and hippocampal brain regions of 3xTg-AD mice. Transcriptomic analysis revealed a significant increase in the expression of neuroinflammation-related genes, accompanied by a significant decrease in neuronal activity-related genes in the OB. Moreover, immunofluorescence and immunoblotting demonstrated an activation of glial cell biomarkers Iba1 and GFAP, along with a reduction in the expression levels of neuronal activity-related molecules Nr4a2 and FosB, as well as olfaction-related marker OMP.

CONCLUSION

In sum, the early accumulation of Aβ and Tau pathology induces neuroinflammation, which subsequently leads to a decrease in neuronal activity within the OB, causing axonal transport deficits that contribute to olfactory disorders. Nr4a2 and FosB appear to be promising targets for intervention aimed at improving early olfactory impairment in AD.

Olfactory Dysfunction Associated with Cognitive Decline in an Elderly Population

BACKGROUND

In many neurological disorders, including Alzheimer disease, early olfactory dysfunction is observed.

OBJECTIVE

In order to determine if deficits in olfactory memory are present in the elderly and if olfactory dysfunction correlates with cognitive impairment in the aging population, olfactory testing has been done on seniors from the NuAge cohort accepting to participate in the Olfactory Response Cognition and Aging (ORCA) secondary sub-study. The t-Mini Mental Statement Examination and the Telephone Interview for Cognitive Status tests were done to assess cognition levels.

RESULTS

Overall, 94% of the ORCA cohort displayed olfactory dysfunction. Deficits in olfactory memory were also present. A correlation was observed between olfactory function and cognitive test scores. Moreover, in women who smoked, there was an association between olfactory memory and cognitive scores.

CONCLUSION

Our results suggest that olfactory dysfunction may predict impending cognitive decline and highlights the need for olfactory training in seniors to improve olfaction and overall well-being.

Unraveling the Link between Olfactory Deficits and Neuropsychiatric Disorders

Smell loss has caught public attention during the recent COVID-19 pandemic. Research on olfactory function in health and disease gains new momentum. Smell deficits have long been recognized as an early clinical sign associated with neuropsychiatric disorders. Here we review research on the associations between olfactory deficits and neuropathological conditions, focusing on recent progress in four areas: (1) human clinical studies of the correlations between smell deficits and neuropsychiatric disorders; (2) development of olfactory mucosa-derived tissue and cell models for studying the molecular pathologic mechanisms; (3) recent findings in brain imaging studies of structural and functional connectivity changes in olfactory pathways in neuropsychiatric disorders; and (4) application of preclinical animal models to validate and extend the findings from human subjects. Together, these studies have provided strong evidence of the link between the olfactory system and neuropsychiatric disorders, highlighting the relevance of deepening our understanding of the role of the olfactory system in pathophysiological processes. Following the lead of studies reviewed here, future research in this field may open the door to the early detection of neuropsychiatric disorders, personalized treatment approaches, and potential therapeutic interventions through nasal administration techniques, such as nasal brush or nasal spray.

Smaller grey matter volume in the central olfactory system in mild cognitive impairment

One of the major challenges in the diagnosis of Alzheimer's disease (AD) is to increase the specificity of the early diagnosis. While episodic memory impairment is a sensitive AD marker, other measures are needed to improve diagnostic specificity. A promising biomarker might be a cerebral atrophy of the central olfactory processing areas in the early stages of the disease since an impairment of olfactory identification is present at the clinical stage of AD. Our goal was therefore, (1) to evaluate the grey matter volume (GMV) of central olfactory processing regions in prodromal AD and (2) to assess its association with episodic memory. We included 34 cognitively normal healthy controls (HC), 92 individuals with subjective cognitive decline (SCD), and 40 with mild cognitive impairment (MCI). We performed regions of interest analysis (ROI) using two different approaches, allowing to extract GMV from (1) atlas-based anatomical ROIs and from (2) functional and non-functional subregions of these ROIs (olfactory ROIs and non-olfactory ROIs). Participants with MCI exhibited smaller olfactory ROIs GMV, including significant reductions in the piriform cortex, amygdala, entorhinal cortex, and left hippocampus compared to other groups (p ≤ 0.05, corrected). No significant effect was found regarding anatomical or non-olfactory ROIs GMV. The left hippocampus olfactory ROI GMV was correlated with episodic memory performance (p < 0.05 corrected). Limbic/medial-temporal olfactory processing areas are specifically atrophied at the MCI stage, and the degree of atrophy might predict cognitive decline in AD early stages.

Olfactory function, neurofilament light chain, and cognitive trajectory: A 12-year follow-up of the Shanghai Aging Study

This study aimed to determine whether blood neurofilament light chain (NfL) modifies the association of olfactory dysfunction (OD) with long-term cognitive decline. A total of 1125 non-demented older adults in the Shanghai Aging Study were evaluated for baseline olfaction (12-item Sniffin' Sticks Smell Test) and cognitive trajectory by a 12-year follow-up. Baseline blood NfL was quantified using Single Molecular Array assay, and dichotomized into low and high levels based on the median value of concentration. The Mini-Mental State Examination (MMSE) and Telephone Interview for Cognitive Status-40 were used to assess participants' cognitive function. Cognitive decline was ascertained when dementia was diagnosed or documented in the medical record during follow-up, or the MMSE declining rate (slope) was 1.0 SD larger than the group mean. OD participants presented a steeper trajectory of MMSE score (p interaction = 0.004) and a high risk of cognitive decline (adjusted HR [95% CI], 1.82 [1.11, 2.98]) only in those with high NfL. Participants with combined OD and high NfL showed the highest risk of cognitive decline (adjusted HR, 2.43 [1.20, 4.92]). OD, especially in combination with high blood NfL concentration, may be able to identify individuals who later incur cognitive deterioration.

Sex differences in olfactory cortex neuronal loss in aging

Introduction

Aging plays a major role in neurodegenerative disorders such as Alzheimer's disease, and impacts neuronal loss. Olfactory dysfunction can be an early alteration heralding the presence of a neurodegenerative disorder in aging. Studying alterations in olfaction-related brain regions might help detection of neurodegenerative diseases at an earlier stage as well as protect individuals from any danger caused by loss of sense of smell.

Objective

To assess the effect of age and sex on olfactory cortex volume in cognitively healthy participants.

Method

Neurologically healthy participants were divided in three groups based on their age: young (20-35 years; n = 53), middle-aged (36-65 years; n = 66) and older (66-85 years; n = 95). T1-weighted MRI scans acquired at 1.5 T were processed using SPM12. Smoothed images were used to extract the volume of olfactory cortex regions.

Results

ANCOVA analyses showed significant differences in volume between age groups in the olfactory cortex (p ≤ 0.0001). In women, neuronal loss started earlier than in men (in the 4th decade of life), while in men more substantial neuronal loss in olfactory cortex regions was detected only later in life.

Conclusion

Data indicate that age-related reduction in the volume of the olfactory cortex starts earlier in women than in men. The findings suggest that volume changes in olfaction-related brain regions in the aging population deserve further attention as potential proxies of increased risk of neurodegenerative diseases.

Could olfactory identification be a prognostic factor in detecting cognitive impairment risk in the elderly?

Aging contributes to the deterioration of the olfactory system in humans. Several studies indicate that the olfactory identification test alone may function as a screening test for olfactory dysfunction and they are more feasible to apply in clinical practice. Olfactory identification may be a predictor for cognitive impairment. Multiple studies have considered the use of odor identification as a measure to identify the conversion from normality to mild cognitive impairment or dementia. The objectives were (i) to elucidate the associations between cognitive status and olfactory identification performance in aging; (ii) understand the predictive value of olfactory capacity in identifying subjects with cognitive impairment risk; and (iii) to study how cognitive status and olfactory identification relate with other variables of wellness in aging, such as functional capabilities and clinical measures. For this purpose, a group of 149 participants (77.15 ± 7.29 years; 73 women of 76.7 ± 8 years and 76 men of 77.6 ± 6.52 years) were recruited and were subjected to a sociodemographic questionnaire, a psychological screening tool of general cognitive status, an olfactory identification evaluation, and clinical measures. The participants were divided into groups based on their cutoff scores of previous scientific reports about the Spanish version of Montreal Cognitive Assessment. Our results indicate an age-associated decline in olfactory identification ability and intensity of odor perception. The predictive ability of olfactory identification scores for the risk of mild and severe impairment is around 80%. Olfactory identification decreases with cognitive function. Performance in odor identification is associated with impairment of episodic memory and executive functions. These findings further our current understanding of the association between cognition and olfaction, and support olfactory assessment in screening those at higher risk of dementia.

Associations of Olfaction With Longitudinal Trajectories of Brain Volumes and Neuropsychological Function in Older Adults

BACKGROUND AND OBJECTIVES

Olfactory function declines with aging, and olfactory deficits are one of the earliest features of neurodegenerative diseases, such as Parkinson disease and Alzheimer disease. Previous studies have shown that olfaction is associated with brain volumes and cognitive function, but data are exclusively cross-sectional. We aimed to examine longitudinal associations of olfaction with changes in brain volumes and neuropsychological function.

METHODS

In the Baltimore Longitudinal Study of Aging, we chose the first assessment of olfaction to examine the associations with retrospective and prospective changes in neuropsychological performance and brain volumes in participants aged 50 years or older using linear mixed-effects models, adjusted for demographic variables and cardiovascular disease. Olfaction was measured as odor identification scores through the 16-item Sniffin' Sticks.

RESULTS

We analyzed data from 567 (58% women, 42% men, 27% Black, 66% White, and 7% others) participants who had data on odor identification scores and brain volumetric MRI (n = 420 with retrospective repeats over a mean of 3.7 years, n = 280 with prospective repeats over a mean of 1.2 years). We also analyzed data from 754 participants (56% women, 44% men, 29% Black, 65% White, and 6% others) with neuropsychological assessments (n = 630 with retrospective repeats over a mean of 6.6 years, n = 280 with prospective repeats over a mean of 1.5 years). After adjustment, higher odor identification scores were associated with prior and subsequent slower brain atrophy in the entorhinal cortex (β ± SE = 0.0093 ± 0.0031, p = 0.0028 and β ± SE = 0.0176 ± 0.0073, p = 0.0169, respectively), hippocampus (β ± SE = 0.0070 ± 0.0030, p = 0.0192 and β ± SE = 0.0173 ± 0.0066, p = 0.0089, respectively), and additional frontal and temporal areas (all p < 0.05). Higher odor identification scores were also associated with prior slower decline in memory, attention, processing speed, and manual dexterity and subsequent slower decline in attention (all p < 0.05). Some associations were attenuated after exclusion of data points at and after symptom onset of cognitive impairment or dementia.

DISCUSSION

In older adults, olfaction is related to brain atrophy of specific brain regions and neuropsychological changes in specific domains over time. The observed associations are driven, in part, by those who developed cognitive impairment or dementia. Future longitudinal studies with longer follow-ups are needed to understand whether olfactory decline precedes cognitive decline and whether it is mediated through regionally specific brain atrophy.

Association between cognition and olfaction-specific parameters in patients with chronic rhinosinusitis

BACKGROUND

Patients with chronic rhinosinusitis (CRS) have reported significantly cognitive and olfactory dysfunction. This study aimed to explore the relationship between cognitive function and olfaction-specific parameters in patients with CRS.

METHODS

A cross-sectional survey method was used to investigate 98 participants, including 75 patients with CRS and 23 healthy controls. Cognitive function and psychophysical olfactory tests were performed. Olfactory cleft endoscopy scale and olfactory cleft computed tomography (CT) scores were obtained. Multivariate logistic regression was used to analyze the risk factors of Mild Cognitive Impairment (MCI) in patients with CRS.

RESULTS

There are significant differences in age, Montreal Cognitive Assessment (MoCA) scores, number of MCI, Lund-Mackay olfactory cleft (LM-OC) score, and blood eosinophil count between CRS with and without olfactory dysfunction groups (all P < 0.05). Total MoCA scores were positively correlated with thresholds-discrimination-identification (TDI) score (r = 0.541, P < 0.001), olfactory threshold (OT) (r = 0.440, P < 0.001), olfactory discrimination (OD) (r = 0.541, P < 0.001), and olfactory identification (OI) (r = 0.382, P = 0.001) scores. Furthermore, total MoCA scores were negatively correlated with LM-OC scores (r =  - 0.351, P = 0.002). After adjusting for patient demographics, only the OD score was an independent risk factor for MCI among patients with CRS (odds ratio = 0.792; P = 0.039). The OD scores less than 11.5 were the best predictor of MCI in patients with CRS.

CONCLUSION

Olfaction-specific clinical parameters were highly correlated with cognitive function in patients with CRS and the OD score was an independent risk factor for MCI in patients with CRS.

Association Between Olfactory Dysfunction and Cognitive Impairment in Dementia-Free Older Adults: A Prospective Cohort Study in Taiwan

BACKGROUND

Previous studies assessing olfactory function and cognition have mostly been cross-sectional, and few have investigated the Asian geriatric population.

OBJECTIVE

To examine the relationships of olfaction with global or domain-specific cognitive function in Taiwanese community-dwelling older adults.

METHODS

This cohort study (2015-2019) is part of the Taiwan Initiative for Geriatric Epidemiological Research. The Taiwanese version of the Montreal Cognitive Assessment (MoCA-T) and a battery of neuropsychological tests were assessed at baseline and at a two-year follow-up. The cross-culture modified Sniffin' Sticks Identification Test (SSIT) was utilized to measure olfactory function. Generalized linear mixed models were used to examine the association of olfaction with cognitive performance over two years.

RESULTS

Data were collected from 376 participants (55.1% women), with a mean age of 75.6 years. A one-point decrease in the SSIT score (worsening of olfaction) was associated with worse global cognition (MoCA-T: βˆ= -0.13), memory (βˆ= -0.08 to -0.06), and verbal fluency (βˆ= -0.07). Compared with an SSIT score ≥ 11 (normosmia), an SSIT score < 8 (anosmia) was associated with worse global cognition (MoCA-T: βˆ= -0.99), memory (βˆ= -0.48 to -0.42), executive function (Trail Making Test A: βˆ= -0.36), attention (digit span backward: βˆ= -0.34), and verbal fluency (βˆ= -0.45). After stratified analyses, the associations remained in older adults ≥ 75 years, males, and non-carriers of apolipoprotein E ɛ4 in terms of global cognition, memory, and verbal fluency.

CONCLUSIONS

Odor identification deficits were associated with poor global or domain-specific cognitive function in a four-year cohort of community-dwelling older adults. Cognitive assessments should be conducted in dementia-free elderly individuals with impaired odor identification.

Odor Discrimination as a Marker of Early Alzheimer's Disease

BACKGROUND

Olfactory dysfunction is an early symptom of Alzheimer's disease (AD). However, olfactory tests are rarely performed in clinical practice because their diagnostic efficacy in detecting early AD is unclear.

OBJECTIVE

To investigate odor discrimination in patients with early AD and the efficacy of olfactory discrimination tests in differentiating these patients from subjects with normal cognition (CN).

METHODS

Thirty patients each with mild dementia due to AD (MD-AD) and mild cognitive impairment due to AD (MCI-AD) and 30 older subjects with CN were enrolled. All participants underwent cognitive examinations (CDR, MMSE, ADAS-Cog 13, and verbal fluency) and odor discrimination tests (Sniffin' Sticks test, Burghart®, Germany).

RESULTS

The MD-AD group achieved significantly worse scores on the olfactory discrimination test than the MCI-AD group, and the MCI-AD group achieved significantly worse results than the CN group (p < 0.05). A cut-off score of≤10 had a diagnostic accuracy of 94.44% (95% CI, 87.51-98.17%) in differentiating patients with MCI-AD/MD-AD from subjects with CN and of 91.67% (95% CI, 81.61-97.24%) in differentiating those with MCI-AD from subjects with CN. Our multinomial logistic regression model with demographic data and ADAS-Cog 13 scores as predictor variables correctly classified 82.2% of the cases (CN, 93.3%; MC-AD, 70%; MD-AD, 83.3%); on adding the olfactory discrimination score to the model, the percentage increased to 92.2% (CN, 96.7%; MCI-AD, 86.7%; MD-AD, 93.3%).

CONCLUSION

Odor discrimination is impaired in cases of early AD and continues to deteriorate as the disease progresses. The olfactory discrimination test showed good diagnostic efficacy in detecting early AD.

Olfaction and declarative memory in aging: a meta-analysis

Olfactory and declarative memory performances are associated, as both functions are processed by overlapping medial-temporal and prefrontal structures and decline in older adults. While a decline in olfactory identification may be related to a decline in declarative memory, the relationship between olfactory detection threshold and declarative memory remains unclear. In this meta-analysis, we assessed (i) the relationship between olfactory identification/detection threshold and verbal declarative memory in cognitively normal older adults, and (ii) the effect of age on these relationships. We included articles from PsychNet, PubMed, and Academic Search Complete according to the following criteria: (i) inclusion of cognitively normal older adults; (ii) assessment of episodic or semantic memory; and (iii) assessment of olfactory identification or detection threshold. Seventeen studies and 22 effect sizes were eligible and included in this meta-analysis. Olfactory identification was associated with episodic (small effect size: r = 0.19; k = 22) and semantic memory (small effect size: r = 0.16; k = 23). Similarly, the olfactory detection threshold was associated with both episodic (small to medium effect size: r = 0.25; k = 5) and semantic memory (small effect size: r = 0.17; k = 7). Age was found to moderate the relationship between olfactory detection threshold and memory performance. Both olfactory identification and detection threshold performances are associated with declarative memory in older adults, and age only moderates the relationship between olfactory detection threshold and declarative memory performances.

Self-Reported Sensory Decline in Older Adults Is Longitudinally Associated With Both Modality-General and Modality-Specific Factors

Background and Objectives

Self-reported sensory data provide important insight into an individual's perception of sensory ability. It remains unclear what factors predict longitudinal change in self-reported sensory ability across multiple modalities during healthy aging. This study examined these associations in a cohort of older adults for vision, hearing, taste, and smell.

Research Design and Methods

Data on self-report sensory ability were drawn from 5,065 participants of The Irish Longitudinal Study on Ageing (mean age at baseline = 61.6, SD = 9.5, range 32-93 years; 59% female; resident in the Republic of Ireland) across 6 waves of data collection (2009-2021). Covariates included demographics, lifestyle factors, and measures of sensory, physical, mental, and cognitive health. Independent discrete survival analyses were performed for each sensory modality.

Results

A transition to self-reported fair/poor hearing was most prevalent (21% of the sample), followed by fair/poor vision (19%), smell (11%), and taste (6%). Participants who self-reported fair/poor function in one sensory modality were likely to report fair/poor ability in another sensory modality, although not for all pairings. Only self-rated fair/poor health was associated with increased odds of self-reported fair/poor ability across all sensory modalities. Age was associated with increased odds of self-reported fair/poor hearing, smell, and taste, as was current smoker status (vision, smell, and taste). Several other sensory (e.g., eye disease, hearing aid use) and nonsensory covariates (e.g., education, depression) were associated with the odds of self-reported fair/poor ability in one or two sensory modalities only.

Discussion and Implications

Over time, older adults perceive associations in fair/poor ability for multiple sensory modalities, albeit somewhat inconsistently. Both modality-general and modality-specific factors are associated with a transition from normal to fair/poor sensory ability. These results suggest the need for more routine testing of multiple senses with increasing age.

Olfactory loss is a predisposing factor for depression, while olfactory enrichment is an effective treatment for depression

The loss of olfactory stimulation correlates well with at least 68 widely differing neurological disorders, including depression, and we raise the possibility that this relationship may be causal. That is, it seems possible that olfactory loss makes the brain vulnerable to expressing the symptoms of these neurological disorders, while daily olfactory enrichment may decrease the risk of expressing these symptoms. This situation resembles the cognitive reserve that is thought to protect people with Alzheimer’s neuropathology from expressing the functional deficit in memory through the cumulative effect of intellectual stimulation. These relationships also resemble the functional response of animal models of human neurological disorders to environmental enrichment, wherein the animals continue to have the induced neuropathology, but do not express the symptoms as they do in a standard environment with restricted sensorimotor stimulation.

Are All Anxieties Created Equal? Stress-related Networks and Anxiety Phenotypes in Old Age

OBJECTIVE

The dysregulation of stress-related networks due to chronic symptoms such as severe worry and/or rumination is one of the putative pathways linking anxiety in late-life with cognitive decline and increased cardiovascular burden. Symptoms such as severe worry or rumination respond poorly to standard treatment and drive the morbidity associated with anxiety in older adults. We assessed if any of the neural networks anchored in the stress-related regions of interest (ROIs) are associated with distinct anxiety phenotypes (worry, rumination and global anxiety).

METHODS

We recruited older participants (over 50 years of age) with varying levels of worry (N = 91) to undergo resting state fMRI. We computed seed-based connectivity for each ROI: the bed nucleus of the stria terminalis, the paraventricular nucleus of the hypothalamus, habenula, and amygdala. We limited our connectivity analyses to extracted regions for each seeded ROI-based network based on their canonical networks in 1,000 participants (Neurosynth). Using connectivity and clinical factors, we fit cross-validated elastic net models to predict scores on Penn State Worry Questionnaire, Rumination Subscale Questionnaire, Hamilton Anxiety Rating Scale, and Perceived Stress Scale.

RESULTS

We identified several distinct connectivity patterns that predict anxiety phenotypes' severity. Greater worry was associated with greater paraventricular nucleus of the hypothalamus -subgenual anterior cingulate cortex, parahippocampal, and olfactory and amygdala-PHC connectivity. Greater global anxiety was associated with lower amygdala-superior temporal gyrus connectivity. Greater perceived stress was associated with lower amygdala-inferior temporal gyrus and amygdala-fusiform gyrus connectivity.

CONCLUSION

Our study suggests that various late-life anxiety phenotypes (worry, global anxiety, rumination) may be associated with varying functional connectivity related to stress and emotion regulation. This may aid in the development of future targeted interventions.

Training with Odors Impacts Hippocampal Thickness in Patients with Mild Cognitive Impairment

Background: The olfactory system is affected early in Alzheimer’s disease and olfactory loss can already be observed in patients with mild cognitive impairment (MCI). Olfactory training is effective for improving olfactory and cognitive function by stimulating the olfactory pathway, but its effect on patients with MCI remains unclear. Objective: The aim of this randomized, prospective, controlled, blinded study was to assess whether a 4-month period of olfactory training (frequent short-term sniffing various odors) may have an effect on olfactory function, cognitive function, and morphology of medial temporal lobe (MTL) subregions and olfactory bulb in MCI patients. Methods: A total of thirty-seven MCI patients were randomly assigned to the training group or a placebo group, which were performed twice a day for 4 months. Olfactory assessments, cognitive tests and magnetic resonance imaging were performed at the baseline and follow-up period. Results: After the training, there was an increase in odor discrimination, and increased cortical thickness of bilateral hippocampus (CA23DG and CA1) and mean MTL. Additionally, the change of olfactory score was positively associated with change of volume of olfactory bulb and hippocampus; the change of global cognition was positively associated with change of cortical thickness of hippocampus, entorhinal cortex and mean MTL; the change of cortical thickness of entorhinal cortex was positively associated with change of executive function. Conclusion: Olfactory training was associated with an increase in cortical thickness of the hippocampus but not olfactory bulb volume in patients with MCI. Olfactory training may serve as an early intervention of preventing hippocampal atrophy.

Biometal Dyshomeostasis in Olfactory Mucosa of Alzheimer's Disease Patients

Olfactory function, orchestrated by the cells of the olfactory mucosa at the rooftop of the nasal cavity, is disturbed early in the pathogenesis of Alzheimer's disease (AD). Biometals including zinc and calcium are known to be important for sense of smell and to be altered in the brains of AD patients. Little is known about elemental homeostasis in the AD patient olfactory mucosa. Here we aimed to assess whether the disease-related alterations to biometal homeostasis observed in the brain are also reflected in the olfactory mucosa. We applied RNA sequencing to discover gene expression changes related to metals in olfactory mucosal cells of cognitively healthy controls, individuals with mild cognitive impairment and AD patients, and performed analysis of the elemental content to determine metal levels. Results demonstrate that the levels of zinc, calcium and sodium are increased in the AD olfactory mucosa concomitantly with alterations to 17 genes related to metal-ion binding or metal-related function of the protein product. A significant elevation in alpha-2-macroglobulin, a known metal-binding biomarker correlated with brain disease burden, was observed on the gene and protein levels in the olfactory mucosa cells of AD patients. These data demonstrate that the olfactory mucosa cells derived from AD patients recapitulate certain impairments of biometal homeostasis observed in the brains of patients.

International consensus statement on allergy and rhinology: Olfaction

BACKGROUND

The literature regarding clinical olfaction, olfactory loss, and olfactory dysfunction has expanded rapidly over the past two decades, with an exponential rise in the past year. There is substantial variability in the quality of this literature and a need to consolidate and critically review the evidence. It is with that aim that we have gathered experts from around the world to produce this International Consensus on Allergy and Rhinology: Olfaction (ICAR:O).

METHODS

Using previously described methodology, specific topics were developed relating to olfaction. Each topic was assigned a literature review, evidence-based review, or evidence-based review with recommendations format as dictated by available evidence and scope within the ICAR:O document. Following iterative reviews of each topic, the ICAR:O document was integrated and reviewed by all authors for final consensus.

RESULTS

The ICAR:O document reviews nearly 100 separate topics within the realm of olfaction, including diagnosis, epidemiology, disease burden, diagnosis, testing, etiology, treatment, and associated pathologies.

CONCLUSION

This critical review of the existing clinical olfaction literature provides much needed insight and clarity into the evaluation, diagnosis, and treatment of patients with olfactory dysfunction, while also clearly delineating gaps in our knowledge and evidence base that we should investigate further.

Single-Cell RNA-Seq Analysis of Olfactory Mucosal Cells of Alzheimer’s Disease Patients

Olfaction is orchestrated by olfactory mucosal cells located in the upper nasal cavity. Olfactory dysfunction manifests early in several neurodegenerative disorders including Alzheimer’s disease, however, disease-related alterations to the olfactory mucosal cells remain poorly described. The aim of this study was to evaluate the olfactory mucosa differences between cognitively healthy individuals and Alzheimer’s disease patients. We report increased amyloid-beta secretion in Alzheimer’s disease olfactory mucosal cells and detail cell-type-specific gene expression patterns, unveiling 240 differentially expressed disease-associated genes compared to the cognitively healthy controls, and five distinct cell populations. Overall, alterations of RNA and protein metabolism, inflammatory processes, and signal transduction were observed in multiple cell populations, suggesting their role in Alzheimer’s disease-related olfactory mucosa pathophysiology. Furthermore, the single-cell RNA-sequencing proposed alterations in gene expression of mitochondrially located genes in AD OM cells, which were verified by functional assays, demonstrating altered mitochondrial respiration and a reduction of ATP production. Our results reveal disease-related changes of olfactory mucosal cells in Alzheimer’s disease and demonstrate the utility of single-cell RNA sequencing data for investigating molecular and cellular mechanisms associated with the disease.

Utility of olfactory identification test for screening of cognitive dysfunction in community-dwelling older adults

Background

There is a need for a large-scale screening test that can be used to detect dementia in older individuals at an early stage. Olfactory identification deficits have been shown to occur in the early stages of dementia, indicating their usefulness in screening tests. This study investigated the utility of an olfactory identification test as a screening test for mild cognitive dysfunction in community-dwelling older people.

Methods

The subjects were city-dwelling individuals aged over 65 years but under 85 years who had not been diagnosed with dementia or mild cognitive impairment. The Japanese version of the Mild Cognitive Impairment Screen was used to evaluate cognitive function. Based on the results, the subjects were divided into two groups: healthy group and cognitively impaired group. Olfactory identification abilities based on the Japanese version of the University of Pennsylvania Smell Identification Test were compared between the groups.

Results

There were 182 participants in total: 77 in the healthy group and 105 in the cognitively impaired group. The mean olfactory identification test score of the cognitively impaired group was significantly lower than that of the healthy group. The cognitive impairment test score was significantly correlated with the olfactory identification test score.

Conclusions

Cross-sectional olfactory identification deficits at baseline in community-dwelling older adults reflected cognitive dysfunction. Assessing olfactory identification ability might be useful as a screening test for mild cognitive dysfunction in community-dwelling older people.

Olfactory dysfunction is associated with cognitive impairment in patients with obstructive sleep apnea: a cross-sectional study

PURPOSE

Obstructive sleep apnea (OSA) increases the risk for olfactory dysfunction. However, the relationship between olfactory function and cognition in OSA patients is unclear. The present study aimed to investigate the relationship between cognition and olfactory dysfunction (OD) in patients with OSA.

METHOD

This was a cross-sectional study in which 74 patients with OSA and 22 controls were recruited. All subjects completed polysomnography, Sniffin' Sticks, and -neurocognitive assessments. According to results of Sniffin' Sticks, OSA patients were divided into two groups: OSA with OD (53 cases) and OSA without OD (21 cases). Neurocognitive function was assessed by Montreal Cognitive Assessment (MoCA), Memory and Executive Screening (MES), and Shape Trail Test (STT). Cognition was compared between OSA with and without OD. Correlation between olfactory parameters and respiratory sleep parameters and neurocognitive assessments was analyzed.

RESULTS

Compared with OSA without OD, OSA with OD showed significantly decreased neurocognitive scores of MoCA (29-27 vs 27-23, p < 0.01), MES-5R (45-40.1 vs 43-33.5, p < 0.01) and increased consuming time of STT-B (91.66 vs 121.63, p < 0.01). A positive correlation was found between the scores of MoCA and MES-5R and all olfactory parameters. In addition, a negative correlation was present between the time consumed for STT-B and odor thresholds (r = - 0.344, p < 0.01), odor identification (r = - 0.335, p < 0.01), and threshold-discrimination-identification scores (r = - 0.448, p < 0.01).

CONCLUSION

Olfactory function is associated cognitive function in patients with OSA and may provide a new direction for early treatment interventions in OSA patients at risk for cognitive impairment.

Diet enriched in omega-3 fatty acids alleviates olfactory system deficits in APOE4 transgenic mice

Olfactory dysfunction is observed in several neurological disorders including Mild Cognitive Impairment (MCI) and Alzheimer disease (AD). These deficits occur early and correlate with global cognitive performance, depression and degeneration of olfactory regions in the brain. Despite extensive human studies, there has been little characterization of the olfactory system in models of AD. In order to determine if olfactory structural and/or molecular phenotypes are observed in a model expressing a genetic risk factor for AD, we assessed the olfactory bulb (OB) in APOE4 transgenic mice. A significant decrease in OB weight was observed at 12 months of age in APOE4 mice concurrent with inflammation and decreased NeuN expression. In order to determine if a diet rich in omega-3s may alleviate the olfactory system phenotypes observed, we assessed WT and APOE4 mice on a docosahexaenoic acid (DHA) diet. APOE4 mice on a DHA diet did not present with atrophy of the OB, and the alterations in NeuN and IBA-1 expression were alleviated. Furthermore, alterations in caspase mRNA and protein expression in the APOE4 OB were not observed with a DHA diet. Similar to the human AD condition, OB atrophy is an early phenotype in the APOE4 mice and concurrent with inflammation. These data support a link between the structural olfactory brain region atrophy and the olfactory dysfunction observed in AD and suggest that inflammation and cell death pathways may contribute to the olfactory deficits observed. Furthermore, the results suggest that diets enriched in DHA may provide benefit to APOE4 allele carriers.

Hippocampal volume is related to olfactory impairment in Parkinson's disease

BACKGROUND AND PURPOSE

Recent evidence has suggested that hyposmia in patients with Parkinson's disease (PD) may be due to impaired central processing. Furthermore, the hippocampus has been regarded as a critical structure linking olfactory impairment and cognitive impairment in PD patients. This study aimed to identify significant structural alterations of the hippocampus in PD patients with hyposmia, and to determine whether these structural changes are significantly associated with olfactory impairment severity.

METHODS

Eighteen idiopathic PD patients with hyposmia and 18 age- and sex-matched PD patients without hyposmia were enrolled. Hippocampal volume and its subfields were measured using FreeSurfer software and compared between hyposmic and normosmic PD patients. We also compared hippocampal substructures' volumes and correlated the hippocampal volumes with hyposmia severity.

RESULTS

PD patients with hyposmia had significantly smaller hippocampal volumes. Among the three components of the hippocampus, the hippocampal body showed a markedly lower volume, which correlated significantly with the cross-cultural smell identification test score that represents olfactory function status. Hippocampal subfield analysis showed that substructures (subiculum, molecular layer) that constitute the hippocampal body showed the most significant volume difference.

CONCLUSIONS

We suggest that atrophy of the bilateral hippocampus implies underlying problems in the central olfaction process in PD patients. In particular, the hippocampus might not only play a critical role in olfaction but could also be important for elucidating possible mechanisms of broad nonmotor symptoms in PD patients.

Joint trajectories of episodic memory and odor identification in older adults: patterns and predictors

Emerging evidence suggests that olfactory function is closely linked to memory function. The aims of this study were to assess whether olfactory and episodic memory functions follow similar age-related decline trajectories, to identify different patterns of decline, as well as predictors of the patterns. 1023 participants from the Memory and Aging Project were followed for up to 8 years with annual episodic memory and odor identification assessments. Trajectories were modelled using growth mixture models. Multivariate logistic regression was used to identify pattern predictors. Three patterns of joint trajectories were identified; Class 1- stable average performance in both functions (n=690, 67.4%); Class 2- stable average episodic memory and declining odor identification (n=231, 22.6%); and Class 3- decline in both functions (n= 102, 10.0%). Class predictors included age, sex, APOE ε4 status, cognitive activity level and BMI. Participants in Class 3 were most likely to develop dementia. Episodic memory and olfactory function show similar trajectories in aging. Such classification can contribute to a better understanding of the factors related to cognitive decline and dementia.

Enhancing GABAergic signaling ameliorates aberrant gamma oscillations of olfactory bulb in AD mouse models

Background

Before the deposition of amyloid-beta plaques and the onset of learning memory deficits, patients with Alzheimer’s disease (AD) experience olfactory dysfunction, typified by a reduced ability to detect, discriminate, and identify odors. Rodent models of AD, such as the Tg2576 and APP/PS1 mice, also display impaired olfaction, accompanied by aberrant in vivo or in vitro gamma rhythms in the olfactory pathway. However, the mechanistic relationships between the electrophysiological, biochemical and behavioral phenomena remain unclear.

Methods

To address the above issues in AD models, we conducted in vivo measurement of local field potential (LFP) with a combination of in vitro electro-olfactogram (EOG), whole-cell patch and field recordings to evaluate oscillatory and synaptic function and pharmacological regulation in the olfactory pathway, particularly in the olfactory bulb (OB). Levels of protein involved in excitation and inhibition of the OB were investigated by western blotting and fluorescence staining, while behavioral studies assessed olfaction and memory function.

Results

LFP measurements demonstrated an increase in gamma oscillations in the OB accompanied by altered olfactory behavior in both APP/PS1 and 3xTg mice at 3–5 months old, i.e. an age before the onset of plaque formation. Fewer olfactory sensory neurons (OSNs) and a reduced EOG contributed to a decrease in the excitatory responses of M/T cells, suggesting a decreased ability of M/T cells to trigger interneuron GABA release indicated by altered paired-pulse ratio (PPR), a presynaptic parameter. Postsynaptically, there was a compensatory increase in levels of GABA_AR α1 and β3 subunits and subsequent higher amplitude of inhibitory responses. Strikingly, the GABA uptake inhibitor tiagabine (TGB) ameliorated abnormal gamma oscillations and levels of GABA_AR subunits, suggesting a potential therapeutic strategy for early AD symptoms. These findings reveal increased gamma oscillations in the OB as a core indicator prior to onset of AD and uncover mechanisms underlying aberrant gamma activity in the OB.

Conclusions

This study suggests that the concomitant dysfunction of both olfactory behavior and gamma oscillations have important implications for early AD diagnosis: in particular, awareness of aberrant GABAergic signaling mechanisms might both aid diagnosis and suggest therapeutic strategies for olfactory damage in AD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13024-021-00434-7.

Olfactory loss and aging: connections with health and well-being

Age-related olfactory dysfunction, or presbyosmia, is a common sensory impairment in aging adults. People in this demographic group with comorbid conditions or exposure to viral, traumatic, or environmental insults remain at the greatest risk for impairment. Several methods for assessing olfaction exist, but they are only available in special settings and require consideration of age, sex, ancestry, and cognition. Perhaps most importantly, olfactory dysfunction has been suggested as an early sign of Alzheimer's and Parkinson's disease and therefore may serve as a tool in the diagnosis and prognosis of these neurodegenerative conditions. Outside of this context, olfactory loss also impacts nutrition, safety, and social relationships, and even predicts mortality itself. This review covers the detection and manifestations of olfactory decline in aging individuals and the myriad ways in which olfactory impairment is connected to their health and well-being.

Scabronine G Methyl Ester Improves Memory-Related Behavior and Enhances Hippocampal Cell Proliferation and Long-Term Potentiation via the BDNF-CREB Pathway in Olfactory Bulbectomized Mice

A previous study reported that scabronine G methyl ester (SG-ME) potentially enhances the in vitro secretion of neurotrophic factors such as nerve growth factor via the protein kinase C (PKC)-ζ pathway. However, it remains unknown whether SG-ME can improve cognitive dysfunctions in olfactory bulbectomized (OBX) mice. To address this question, we evaluated SG-ME-treated and untreated OBX mice in a passive avoidance test. We also investigated potential effects of SG-ME on several parameters: cell proliferation and cAMP response element-binding protein (CREB) phosphorylation in the hippocampal dentate gyrus by immunohistochemistry, brain-derived neurotrophic factor (BDNF) levels in the hippocampus by Western blotting, p-CREB levels in the hippocampus by MapAnalyzer, and long-term potentiation (LTP) by electrophysiology. On the 14th day after surgery OBX mice showed altered passive avoidance and decreases in both cell proliferation and long-term potentiation in the hippocampus, while these changes were reversed by SG-ME (20 μg/mouse) 24 h after the treatment. The improvement in memory deficits was prevented when SG-ME was co-administeredwith either zeta inhibitory peptide (PKC-ζ inhibitor), anti-BDNF antibody, ANA-12 (TrkB antagonist), U0126 (MEK inhibitor), H-89 (PKA inhibitor), LY294002 (PI3K inhibitor) or KN-93 (CaMKII inhibitor). We found that SG-ME enhanced brain-derived neurotrophic factor and p-CREB levels in the hippocampus while p-CREB was localized in neurons, but not in astrocytes nor microglial cells. These findings revealed the potential of SG-ME in improving memory impairments by enhancing cell proliferation and LTP via activation of the BDNF/CREB signaling pathway in neurons.

The Peripheral Hearing and Central Auditory Processing Skills of Individuals With Subjective Memory Complaints

Purpose

This study examined the central auditory processing (CAP) assessment results of adults between 45 and 85 years of age with probable pre-clinical Alzheimer’s disease – i.e., individuals with subjective memory complaints (SMCs) as compared to those who were not reporting significant levels of memory complaints (non-SMCs). It was hypothesized that the SMC group would perform significantly poorer on tests of central auditory skills compared to participants with non-SMCs (control group).

Methods

A total of 95 participants were recruited from the larger Western Australia Memory Study and were classified as SMCs (N = 61; 20 males and 41 females, mean age 71.47 ±7.18 years) and non-SMCs (N = 34; 10 males, 24 females, mean age 68.85 ±7.69 years). All participants completed a peripheral hearing assessment, a CAP assessment battery including Dichotic Digits, Duration Pattern Test, Dichotic Sentence Identification, Synthetic Sentence Identification with Ipsilateral Competing Message (SSI-ICM) and the Quick-Speech-in-Noise, and a cognitive screening assessment.

Results

The SMCs group performed significantly poorer than the control group on SSI-ICM −10 and −20 dB signal-to-noise conditions. No significant differences were found between the two groups on the peripheral hearing threshold measurements and other CAP assessments.

Conclusions

The results suggest that individuals with SMCs perform poorly on specific CAP assessments in comparison to the controls. The poor CAP in SMC individuals may result in a higher cost to their finite pool of cognitive resources. The CAP results provide yet another biomarker that supports the hypothesis that SMCs may be a primary indication of neuropathological changes in the brain. Longitudinal follow up of individuals with SMCs, and decreased CAP abilities should inform whether this group is at higher risk of developing dementia as compared to non-SMCs and those SMC individuals without CAP difficulties.

Olfactory impairment and the risk of cognitive decline and dementia in older adults: a meta-analysis

Introduction

The prediction of the impact of olfactory impairment on cognitive decline in older adults has been different among different age groups.

Objective

This meta-analysis sought to estimate the predictive power of olfactory impairment on cognitive decline during follow-up in older adults of different ages.

Material and methods

A medical literature search was carried out using these databases for eligible studies: MEDLINE, COCHRANE and EMBASE. Studies recording olfaction and cognition detection at the beginning and end of the follow-up were included in the preliminary screening. The medical records of older adults without cognitive impairment at the beginning of the follow-up were taken into account in this analysis. Raw data was extracted in order to estimate the relative risk and the corresponding 95% confidence interval (95% CI). Subgroup analysis of age was performed to eliminate the effect of age on the results. Statistical heterogeneity was measured using the I² index and Cochran's Q test.

Results

Eight studies were enrolled in this analysis (3237 events and 13165 participants), and the pooled relative risk for the 70–80 years old subgroup was 2.00 (95% CI = 1.79–2.23).

Conclusion

Relatively, there is a higher risk of cognitive impairment at the end of follow-up in younger adults with olfactory impairment at the beginning of follow-up. The length of follow-up has a little effect on the relative risk.

Smell, an Underrated Early Biomarker for Brain Aging

Olfaction is in addition to touch the most ancient of our senses, developing already in the womb it decays progressively from 65 years of age with a more pronounced impairment associated with dementia. Despite its clinical relevance and testing accessibility, smell remains an overlooked biomarker, which is rarely used by neurologists in the early screening phase. In this perspective article, we outline the reasons underlying the lack of awareness for this sense. In an attempt to put olfaction forward as an early biomarker for pathological brain aging, we draw a comparison with vision and hearing, regarded as more relevant for general health. This perspective article wants to encourage further studies aimed at understanding the mechanisms responsible for the early smell dysfunction in individuals a decade or more before the onset of cognitive symptoms.

Olfactory dysfunction in frontotemporal dementia and psychiatric disorders: A systematic review

Frontotemporal dementia (FTD) is a progressive neurodegenerative disease. Diagnosis of FTD, especially the behavioural variant, is challenging because of symptomatic overlap with psychiatric disorders (depression, schizophrenia, bipolar disorder). Olfactory dysfunction is common in both FTD and psychiatric disorders, and often appears years before symptom onset. This systematic review analysed 74 studies on olfactory function in FTD, depression, schizophrenia and bipolar disorder to identify differences in olfactory dysfunction profiles, focusing on the most common smell measures: odour identification and discrimination. Results revealed that FTD patients were severely impaired in odour identification but not discrimination; in contrast, patients diagnosed with schizophrenia showed impairments in both measures, while those diagnosed with depression showed no olfactory impairments. Findings in bipolar disorder were mixed. Therefore, testing odour identification and discrimination differentiates FTD from depression and schizophrenia, but not from bipolar disorder. Given the high prevalence of odour identification impairments in FTD, and that smell dysfunction predicts neurodegeneration in other diseases, olfactory testing seems a promising avenue towards improving diagnosis between FTD and psychiatric disorders.

Comparison of Noninvasive Imagery Methods to Observe Healthy and Degenerated Olfactory Epithelium in Mice for the Early Diagnosis of Neurodegenerative Diseases

Olfactory dysfunction could be an early and reliable indicator for the diagnosis of neurodegenerative disorders such as Alzheimer and Parkinson's diseases. In this paper, we compare the potential of different noninvasive medical imaging modalities (optical coherence tomography, confocal microscopy, and fluorescence endomicroscopy) to distinguish how the olfactory epithelium, both at the cellular and the structural levels, is altered. Investigations were carried out on three experimental groups: two pathological groups (mice models with deliberately altered olfactory epithelium and Alzheimer's disease transgenic mice models) were compared with healthy mice models. As histological staining, the three tested noninvasive imaging tools demonstrated the general tubular organization of the olfactory epithelium on healthy mice. Contrary to OCT, confocal microscopy, and endomicroscopy allowed visualizing the inner structure of olfactory epithelium as well as its morphological or functional changes on pathological models, alterations classically observed with histological assessment. The results could lead to relevant development of imaging tools for noninvasive and early diagnosis of neurodegenerative diseases through the in situ characterization of the olfactory epithelium.

A Community-Based Study on the Prevalence of Olfactory Dysfunction

BACKGROUND

Olfactory dysfunction (OD) is common, affecting an estimated 13 million adults in the United States. Prior studies may underestimate OD prevalence due to use of brief smell identification tests or age-adjusted cutoff values, which concede that it is acceptable for older people to have a decreased sense of smell.

OBJECTIVE

To determine OD prevalence in the healthy community when the goal and expectation is ideal olfactory function, rather than age-based population norms. Secondary goals were to explore factors associated with OD.

METHODS

Subjects without otolaryngic complaints were recruited from the community surrounding the Medical University of South Carolina. Olfactory-specific information was collected, and olfactory function was assessed using the Sniffin' Sticks test (Burghardt, Wedel, Germany) to measure threshold, discrimination, and identification (TDI). OD was defined as a TDI score < 31. Bivariate analysis and linear regression were used to determine factors associated with OD.

RESULTS

In total, 176 subjects were included with mean age of 52 years (range: 20-93), 111 (63%) female, and 127 (72%) white. Mean TDI score was 28.8 (6.9) and OD was present in 94 (53%) subjects. Multivariate linear regression revealed that TDI decreased an average of 1 point every 5 years. TDI was also associated with Mini-Mental Status Examination (MMSE) score, asthma, and gastroesophageal reflux disease. Threshold was associated with age, heart problems, and gastroesophageal reflux disease. Discrimination was associated with age and MMSE scores. Identification was associated with age, heart problems, and anxiety.

CONCLUSIONS

In a community-based sample, OD affects greater than 50% of subjects. Aging impacts all aspects of olfaction, while the effects of factors such as asthma, MMSE scores, gastroesophageal reflux disease, heart problems, and anxiety may only be evident in specific olfactory subtests.

Cognitive, Olfactory, and Affective Determinants of Body Weight in Aging Individuals

OBJECTIVE

A complex interplay of factors including cognitive, sensory and affective aspects has been associated in a controversial way with anthropometric measures related to body weight.

METHODS

Here we propose two studies to investigate whether and how cognitive, olfactory and affective variables resulted associated with body weight during healthy aging. In Study 1, we investigated the cognitive status, the odor identification skills, and the BMI of 209 individuals (50-96 yo). In Study 2 an extensive evaluation of cognitive functions (in particular executive functions and memory), odor threshold, discrimination and identification and affective skills (i.e., depression and anxiety) was performed in a group of 35 healthy, free-living aging individuals (58-85 yo).

RESULTS

In Study 1, greater BMI was not associated with performance on the odor identification task but was significantly associated with better cognitive skills. In Study 2, we observed that executive functions seemed to favor a successful managing of body weight, and individuals with greater BMI and waist circumference showed significantly better odor discrimination skills. Finally, lower waist circumference (but not BMI) was found significantly associated with greater levels of anxiety.

CONCLUSIONS

These results confirm that cognitive, olfactory and affective factors may influence body weight during healthy aging.

Intranasal administration of orexin peptides: Mechanisms and therapeutic potential for age-related cognitive dysfunction

Cognitive impairment is a core feature of several neuropsychiatric and neurological disorders, including narcolepsy and age-related dementias. Current pharmacotherapeutic approaches to cognitive enhancement are few in number and limited in efficacy. Thus, novel treatment strategies are needed. The hypothalamic orexin (hypocretin) system, a central integrator of physiological function, plays an important role in modulating cognition. Several single- and dual-orexin receptor antagonists are available for various clinical and preclinical applications, but the paucity of orexin agonists has limited the ability to research their therapeutic potential. To circumvent this hurdle, direct intranasal administration of orexin peptides is being investigated as a prospective treatment for cognitive dysfunction, narcolepsy or other disorders in which deficient orexin signaling has been implicated. Here, we describe the possible mechanisms and therapeutic potential of intranasal orexin delivery. Combined with the behavioral evidence that intranasal orexin-A administration improves cognitive function in narcoleptic and sleep-deprived subjects, our neurochemical studies in young and aged animals highlights the capacity for intranasal orexin administration to improve age-related deficits in neurotransmission. In summary, we highlight prior and original work from our lab and from others that provides a framework for the use of intranasal orexin peptides in treating cognitive dysfunction, especially as it relates to age-related cognitive disorders.

Intact global cognitive and olfactory ability predicts lack of transition to dementia

INTRODUCTION

Odor identification deficits characterize Alzheimer's disease and other dementias. We examined if intact performance on brief cognitive and odor identification tests predicts lack of transition to dementia.

METHODS

In an urban community, 1037 older adults without dementia completed the 40-item University of Pennsylvania Smell Identification Test, which includes the 12-item Brief Smell Identification Test (B-SIT). Data from 749 participants followed up for 4 years were analyzed.

RESULTS

In covariate-adjusted survival analyses, impairment on the Blessed Orientation Memory Concentration Test and B-SIT each predicted dementia (n = 109), primarily Alzheimer's disease (n = 101). Among participants with intact olfactory (B-SIT ≥ 11/12 correct) and cognitive (Blessed Orientation Memory Concentration Test ≤ 5/28 incorrect) ability, 3.4% (4/117) transitioned to dementia during follow-up with no transitions in the 70-75 and 81-83 years age group quartiles.

DISCUSSION

Odor identification testing adds value to global cognitive testing, and together can identify individuals who rarely transition to dementia, thereby avoiding unnecessary diagnostic investigation.

Effects of Intranasal Orexin-A (Hypocretin-1) Administration on Neuronal Activation, Neurochemistry, and Attention in Aged Rats

Cognitive function represents a key determinative factor for independent functioning among the elderly, especially among those with age-related cognitive disorders. However; existing pharmacotherapeutic tactics for treating these disorders provide only modest benefits on cognition. The hypothalamic orexin (hypocretin) system is uniquely positioned, anatomically and functionally, to integrate physiological functions that support proper cognition. The ongoing paucity of orexin receptor agonists has mired the ability to study their potential as cognitive enhancers. Fortunately, intranasal administration of native orexin peptides circumvents this issue and others concerning peptide transport into the central nervous system (CNS). To investigate the ability of intranasal orexin-A (OxA) administration to improve the anatomical, neurochemical, and behavioral substrates of age-related cognitive dysfunction, these studies utilized a rodent model of aging combined with acute intranasal administration of saline or OxA. Here, intranasal OxA increases c-Fos expression in several telencephalic brain regions that mediate important cognitive functions, increases prefrontal cortical acetylcholine efflux, and alters set-shifting-mediated attentional function in rats. Ultimately, these studies provide a framework for the possible mechanisms and therapeutic potential of intranasal OxA in treating age-related cognitive dysfunction.

Validation of Iranian Smell Identification Test for screening of mild cognitive impairment and Alzheimer's disease

Background: According to the World Alzheimer Report 2019, an estimated 50 million people worldwide are living with dementia. The smell test is a method for early detection of Alzheimer's disease (AD) as an inexpensive, simple, and noninvasive screening tool. This study aimed to evaluate the accuracy of the Iran Smell Identification Test (Iran-SIT) in discriminating patients with AD, with mild cognitive impairment (MCI), and the healthy subjects.Methods: In this study, 42 patients with AD, 33 with MCI, and 32 healthy controls were recruited from the referral Memory Clinic of Tehran University of Medical Sciences. The olfactory function was examined with six odors through Iran-SIT.Results: We found a significant difference among the olfactory function in subjects with normal cognitive status, that of those with MCI and those with AD (p < 0.001). The cutoff point for the diagnosis of AD was (sensitivity and specificity were, respectively, 85.7 and 90.8%), and (Sensitivity and specificity were, respectively, 93.9 and 100%) for MCI.Conclusion: These results suggest that Iran-SIT is a valid biomarker and practical screening tool, with simple, inexpensive, and readily available for use in combination with neuropsychological tools and neuroimaging for early detection of AD.

Analyses of Clinical Features and Investigations on Potential Mechanisms in Patients with Alzheimer's Disease and Olfactory Dysfunction

BACKGROUND

OD is common in patients with Alzheimer's disease (AD). However, the relationship between OD and clinical symptoms and the potential mechanisms of OD in AD patients are still unknown.

OBJECTIVE

To explore the relationship between OD and clinical symptoms and the potential mechanisms of OD in AD patients.

METHODS

We evaluated OD using the Hyposmia Rating Scale (HRS), classified patients into AD with OD (AD-OD) and AD with no OD (AD-NOD) groups, and detected the levels of free radicals and inflammatory factors, including hydroxyl radical (•OH), hydrogen peroxide (H2O2), nitric oxide, interleukin-1β, interleukin-6, tumor necrosis factor-α, and prostaglandin E2 in serum from AD patients.

RESULTS

It was shown that the scores of the Mini-Mental State Examination, Animal Fluency Test, Boston Naming Test (BNT), and Auditory Verbal Learning Test-delayed recall were all significantly lower and the score of overall activity of daily living (ADL) and instrumental ADL were significantly higher in AD-OD group than those in AD-NOD group. Compared with AD-NOD group, •OH level in serum was prominently elevated, and H2O2 level was dramatically declined in AD-OD group. In the correlation analysis, HRS score was significantly and positively correlated with the score of BNT, and negatively correlated with •OH level in serum.

CONCLUSIONS

AD-OD patients suffered from severe cognitive impairment in the domain of language. Oxidative stress might be correlated with AD-OD featured by the drastically increased •OH level in serum.

Olfactory Function is Associated with Cognitive Performance: Results of the Heinz Nixdorf Recall Study

BACKGROUND

There is strong evidence for an association of olfactory dysfunction and neurodegenerative diseases. Studies on the association of olfaction and cognition in the general population are rare.

OBJECTIVE

To evaluate gender- and age-specific associations of olfactory function and cognitive performance in a well characterized population-based study sample.

METHODS

At the third examination of the Heinz Nixdorf Recall study (n = 3,087), 2,640 participants (48% men; 68.2±7.2 years) underwent Sniffin' Sticks Screening Test measuring olfactory function on a scale of 0-12 points. Olfactory function was rated as anosmic, hyposmic, or normosmic (≤6, 7-10 or ≥11 points, respectively). All participants performed eight validated cognitive subtests. Age- (55-64 years, 65-74 years, 75-86 years) and gender-stratified multivariate analysis of covariance was used to evaluate group differences in cognitive performance.

RESULTS

Women showed better olfactory function than men (p < 0.001). For middle-aged participants, olfactory groups differed in almost all cognitive subtests. The analyses revealed no gender effects, although associations were slightly greater for women than for men. Anosmics showed the worst cognitive performance and normosmics showed the best cognitive performance. In the young- and old-aged groups, a quantitative association was found for anosmics in all subtests and for normosmics and hyposmics in almost all subtests.

CONCLUSION

This is the first study reporting on age-specific associations of olfactory function and cognitive performance in the general population. The association found in middle-aged participants (65-74 years) may serve as a marker to improve identification of persons at high risk for cognitive decline and dementia.