Olfactory memory in the old and very old: relations to episodic and semantic memory and APOE genotype

Olfactory Deficits and Mortality in Older Adults

Importance

Olfactory deficits are associated with higher mortality in older adults, but the mechanisms remain unclear. Further understanding this relationship could inform interventions to improve survival and quality of life for those with olfactory deficits.

Objective

To investigate the association of olfactory deficits with all-cause and cause-specific mortality and to explore potential mediating factors.

Design, Setting, and Participants

The Swedish National Study on Aging and Care in Kungsholmen (SNAC-K), is an ongoing population-based, longitudinal cohort study with baseline between 2001 and 2004. Eligible participants were residents of Kungsholmen, Stockholm, Sweden, and aged between 60 and 99 years from March 21, 2001, to August 30, 2004. Twelve-year follow-up was completed in February 2013. Data analysis took place between February 2024 and July 2024.

Main Outcomes and Measures

Olfactory ability was tested with the 16-item Sniffin' Sticks Odor Identification task. Mortality was determined through the Swedish National Cause of Death Register. Cox proportional hazards models examined the associations between olfaction and mortality over 6 years and 12 years. Competing hazard risks regression analyses assessed the olfactory-mortality association for specific death causes. Generalized structural equation models investigated mediators, including incident dementia, baseline chronic diseases, frailty, and malnutrition. The tested hypotheses were formulated after data collection.

Results

Among 2524 participants (baseline mean [SD] age, 71.9 [10.0] years; 1545 [61.2%] female), 445 (17.6%) had died at 6 and 969 (38.4%) at 12 years of follow-up. Each additional incorrect answer on the odor identification test was associated with a 6% increased all-cause mortality risk at 6 years (hazard ratio [HR], 1.06 [95% CI, 1.03-1.08]) and 5% increased risk at 12 years (HR, 1.05 [95% CI, 1.03-1.08]) in multiadjusted models. In cause-specific models, the olfaction-mortality association had the greatest risk in relation to neurodegenerative death causes. Meaningful mediators for death at 6 years included dementia (23% of total association), frailty (11% of total association), and malnutrition (5% of total association). At 12 years, frailty remained a mediator (9% of total association).

Conclusions and Relevance

The results of this cohort study underscore the importance of olfactory function as a mortality risk marker in older adults and highlight the evolving influence of neurodegeneration and frailty on this relationship. Further research is needed to assess the clinical utility of olfactory assessments in identifying individuals at risk of adverse health outcomes.

Cerebrovascular burden and neurodegeneration linked to 15-year odor identification decline in older adults

Background

The mechanisms underlying olfactory decline in aging need further investigation. Noticeably, the longitudinal relationship of biological markers with olfaction remains underexplored. We investigated whether baseline levels and progression of microvascular lesions and brain atrophy are associated with odor identification (OID) decline.

Methods

The association between structural MRI markers and OID decline was examined in participants from the SNAC-K MRI study who were free from dementia at baseline (n = 401, mean age = 70.2 years, 60% females). OID was repeatedly assessed over 15 years. Presence of lacunes, white matter hyperintensities (WMH), perivascular spaces (PVS), and lateral ventricular, hippocampal, amygdalar, and total gray matter (GM) volumes were assessed up to 6 years, concurrent with the first 6 years of olfactory assessments.

Results

Higher PVS count and lower hippocampal and GM volumes at baseline were associated with accelerated OID decline (pFWE  < 0.05). Longitudinally (n = 225), presence of lacunes at follow-up, faster WMH volume and PVS count increases, faster lateral ventricular enlargement, and faster hippocampal, amygdalar, and GM atrophy were associated with accelerated OID decline (p FWE < 0.05).

Conclusion

Olfactory decline is related to both increased cerebrovascular burden and accelerated brain atrophy over time.

The AROMHA brain health test is a remote olfactory assessment to 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.

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.

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.

A Rose by Another Name? Odor Misnaming is Associated with Linguistic Properties

Naming common odors is a surprisingly difficult task: Odors are frequently misnamed. Little is known about the linguistic properties of odor misnamings. We test whether odor misnamings of old adults carry information about olfactory perception and its connection to lexical-semantic processing. We analyze the olfactory-semantic content of odor source naming failures in a large sample of older adults in Sweden (n = 2479; age 58-100 years). We investigate whether linguistic factors and semantic proximity to the target odor name predict how odors are misnamed, and how these factors relate to overall odor identification performance. We also explore the primary semantic dimensions along which misnamings are distributed. We find that odor misnamings consist of surprisingly many vague and unspecific terms, such as category names (e.g., fruit) or abstract or evaluative terms (e.g., sweet). Odor misnamings are often strongly associated with the correct name, capturing properties such as its category or other abstract features. People are also biased toward misnaming odors with high-frequency terms that are associated with olfaction or gustation. Linguistic properties of odor misnamings and their semantic proximity to the target odor name predict odor identification performance, suggesting that linguistic processing facilitates odor identification. Further, odor misnamings constitute an olfactory-semantic space that is similar to the olfactory vocabulary of English. This space is primarily differentiated along pleasantness, edibility, and concreteness dimensions. Odor naming failures thus contain plenty of information about semantic odor knowledge.

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.

The effect of the apolipoprotein E ε4 allele and olfactory function on odor identification networks

INTRODUCTION

The combination of apolipoprotein E ε4 (ApoE ε4) status, odor identification, and odor familiarity predicts conversion to mild cognitive impairment (MCI) and Alzheimer's disease (AD).

METHODS

To further understand olfactory disturbances and AD risk, ApoE ε4 carrier (mean age 76.38 ± 5.21) and ε4 non-carrier (mean age 76.8 ± 3.35) adults were given odor familiarity and identification tests and performed an odor identification task during fMRI scanning. Five task-related functional networks were detected using independent components analysis. Main and interaction effects of mean odor familiarity ratings, odor identification scores, and ε4 status on network activation and task-modulation of network functional connectivity (FC) during correct and incorrect odor identification (hits and misses), controlling for age and sex, were explored using multiple linear regression.

RESULTS

Findings suggested that sensory-olfactory network activation was positively associated with odor identification scores in ε4 carriers with intact odor familiarity. The FC of sensory-olfactory, multisensory-semantic integration, and occipitoparietal networks was altered in ε4 carriers with poorer odor familiarity and identification. In ε4 carriers with poorer familiarity, connectivity between superior frontal areas and the sensory-olfactory network was negatively associated with odor identification scores.

CONCLUSIONS

The results contribute to the clarification of the neurocognitive structure of odor identification processing and suggest that poorer odor familiarity and identification in ε4 carriers may signal multi-network dysfunction. Odor familiarity and identification assessment in ε4 carriers may contribute to the predictive value of risk for MCI and AD due to the breakdown of sensory-cognitive network integration. Additional research on olfactory processing in those at risk for AD is warranted.

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.

Odor Identification Across Time in Mutation Carriers and Non-Carriers in Autosomal-Dominant Alzheimer's Disease

BACKGROUND

Impaired odor identification is a characteristic of sporadic Alzheimer'sdisease(AD), but its presence in autosomal-dominantAD (adAD) remains uncertain.

OBJECTIVE

To investigate odor identification ability in mutation carriers (MC) and non-carriers (NC) of adAD in relation to years to estimated clinical onset clinical onset (YECO) of disease.

METHODS

Participants from six families with autosomal-dominant mutations (APP Swedish, APP Arctic, and PSEN1 mutations) included 20 MC and 20 NC. The groups were comparable in age, gender, education, number of APOE ɛ4 alleles, and YECO, but differed in global cognition (Mini-Mental State Examination). The MC group included individuals in asymptomatic, symptomatic cognitively unimpaired, mild cognitive impairment, and dementia stages of disease, spanning approximately 40 years of the AD continuum. All NC were asymptomatic. Olfactory function was assessed by means of free and cued identification of common odors summarized as total identification.

RESULTS

MC performed poorer than NC in free and total identification. Four MC and none of the NC were anosmic. Olfactory functions in MC and NC were significantly and inversely related to time course (YECO) for both free and total identification. The decline in free identification began approximately 10 years prior to the estimated clinical onset of AD in MC. Odor identification proficiency was associated with episodic memory and executive function in MC and NC.

CONCLUSIONS

Impaired odor identification is present well before the clinical diagnosis of AD in MC and is associated with disease progression. Odor identification ability may be a useful early biomarker for adAD.

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 memory in mild cognitive impairment and Alzheimer's disease

Introduction

Olfaction is impaired in Alzheimer's disease (AD). However, olfactory memory has rarely been examined. As the pathogenesis of AD remains largely unknown, collecting more data regarding the occurrence and progression of its symptoms would help gain more insight into the disease.

Objective

To investigate olfactory memory and its relationship with verbal memory and other clinical features in patients with early-stage AD.

Methods

Three groups of participants were enrolled in this study: patients with mild dementia due to AD (MD-AD, N = 30), patients with mild cognitive impairment due to AD (MCI-AD, N = 30), and cognitively normal older participants (CN, N = 30). All participants underwent cognitive evaluation (Clinical Dementia Rating scale, Mini Mental State Examination, Alzheimer's Disease Assessment Scale-Cognitive Subscale, delayed verbal recall, and verbal fluency tests) and assessment of olfactory immediate and delayed recognition memory.

Results

Olfactory immediate and delayed recognition memory scores were significantly lower in the MD-AD group than in the MCI-AD and CN groups. The MCI-AD and CN groups did not differ significantly [in both cases, Kruskal-Wallis test, p < 0.05; post hoc analysis revealed significant differences between the MD-AD and MCI-AD groups and between the MD-AD and CN groups (p < 0.05), and no significant difference between the MCI-AD and CN groups (p > 0.05)]. Verbal immediate recall, delayed recall after 5 min, and delayed recall after 30 min scores were significantly worse in the MD-AD and MCI-AD groups than in the CN group. MD-AD and MCI-AD groups did not differ significantly [in all cases Kruskal-Wallis test, p < 0.05; post hoc analysis revealed significant differences between MD-AD and CN groups, and MCI-AD and CN groups (p < 0.05) and no significant difference between MD-AD and MCI-AD groups (p > 0.05)]. Duration of AD symptoms was a strong predictor of both immediate and delayed olfactory recognition memory scores.

Conclusion

Olfactory memory impairment was observed in patients with AD. The changes progress during the course of the disease. However, unlike verbal memory, olfactory memory is not significantly impaired in the prodromal stage of AD.

Odor identification errors reveal cognitive aspects of age-associated smell loss

Human olfaction can be extraordinarily sensitive, and its most common assessment method is odor identification (OID), where everyday odors are matched to word labels in a multiple-choice format. However, many older persons are unable to identify familiar odors, a deficit that is associated with the risk of future dementia and mortality. The underlying processes subserving OID in older adults are poorly understood. Here, we analyzed error patterns in OID to test whether errors could be explained by perceptual and/or semantic similarities among the response alternatives. We investigated the OID response patterns in a large, population-based sample of older adults in Sweden (n = 2479; age 60-100 years). Olfaction was assessed by a 'Sniffin ́ TOM OID test with 16 odors; each trial involved matching a target odor to a correct label among three distractors. We analyzed the pattern of misidentifications, and the results showed that some distractors were more frequently selected than others, suggesting cognitive or perceptual factors may be present. Relatedly, we conducted a large online survey of older adults (n = 959, age 60-90 years) who were asked to imagine and rate the perceptual similarity of the target odors and the three corresponding distractors (e.g. "How similar are these smells: apple and mint?"). We then used data from the Swedish web corpus and the Word2Vec neural network algorithm to quantify the semantic association strength between the labels of each target odor and its three distractors. These data sources were used to predict odor identification errors. We found that the error patterns were partly explained by both the semantic similarity between target-distractor pairs, and the imagined perceptual similarity of the target-distractor pair. Both factors had, however, a diminished prediction in older ages, as responses became gradually less systematic. In sum, our results suggest that OID tests not only reflect olfactory perception, but also likely involve the mental processing of odor-semantic associations. This may be the reason why these tests are useful in predicting dementia onset. Our insights into olfactory-language interactions could be harnessed to develop new olfactory tests that are tailored for specific clinical purposes.

Markers of olfactory dysfunction and progression to dementia: A 12-year population-based study

INTRODUCTION

We evaluated markers of olfactory dysfunction (OD) for estimating hazard of dementia in older adults.

METHODS

Mild (hyposmia) and severe (anosmia) OD was classified in a population-based study of dementia-free persons (SNAC-K; n = 2473; mean age = 70 years) using the Sniffin sticks odor identification task. Combined variables were created for objective and subjective OD and for OD and APOE status. Hazard of dementia across 12 years was estimated with Cox regression.

RESULTS

OD was associated with increased hazard of dementia (2.01; 95% confidence interval [CI] 1.60-2.52), with the strongest association for anosmia (2.92; 95% CI 2.14-3.98). Results remained consistent after adjusting for potential confounders and across age and sex subgroups. APOE ε4 carriers with anosmia had the highest hazard of dementia (ε4: 6.95; 95% CI 4.16-11.62; ε4/ε4: 19.84; 95% CI 6.17-63.78).

DISCUSSION

OD is associated with increased risk of dementia, especially severe impairment in combination with genetic risk of Alzheimer's disease.

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.

Perceptual odor qualities predict successful odor identification in old age

Odor identification is a common assessment of olfaction, and it is affected in a large number of diseases. Identification abilities decline with age, but little is known about whether there are perceptual odor features that can be used to predict identification. Here, we analyzed data from a large, population-based sample of 2,479 adults, aged 60 years or above, from the Swedish National study on Aging and Care in Kungsholmen. Participants performed both free and cued odor identification tests. In a separate experiment, we assessed perceived pleasantness, familiarity, intensity, and edibility of all odors in the first sample, and examined how odor identification performance is associated with these variables. The analysis showed that high-intensity odors are easier to identify than low-intensity odors overall, but also that they are more susceptible to the negative repercussions of old age. This result indicates that sensory decline is a major aspect of age-dependent odor identification impairment, and suggests a framework where identification likelihood is proportional to the perceived intensity of the odor. Additional analyses further showed that high-performing individuals can discriminate target odors from distractors along the pleasantness and edibility dimensions and that unpleasant and inedible odors show smaller age-related differences in identification. Altogether, these results may guide further development and optimization of brief and efficient odor identification tests as well as influence the design of odorous products targeted toward older consumers.

Reduced Olfactory Memory Performance Is Associated with Executive Function Deficits in Older Adults

INTRODUCTION

Previous research has identified an association between olfactory impairment (reduced odor sensitivity/ identification/ discrimination) and cognitive impairment in older adults. The present study focused on the relationship between olfactory memory performance and cognitive/affective functioning.

METHOD

Recognition performance for olfactory and visual stimuli (control condition) was tested through a matching task in older adults (n = 44; M_age = 76 years) and younger adults (n = 56; M_age = 24 years). Additionally, negative affect (anxiety, depression) and cognitive functioning were assessed via validated questionnaires and a neuropsychological test battery.

RESULTS

The older participants performed worse than the younger adults in the olfactory memory task. In older adults, difficulties in remembering odors were associated with reduced odor identification and executive functioning (reduced cognitive flexibility). Affective well-being was not related to olfactory memory performance.

IMPLICATION

Olfactory memory impairment in older adulthood might be a marker for cognitive decline in areas related to executive functions.

The Western Australia Olfactory Memory Test: Reliability and Validity in a Sample of Older Adults

Objective

The Western Australia Olfactory Memory Test (WAOMT) is a newly developed test designed to meet a need for a comprehensive measure of olfactory episodic memory (OEM) for clinical and research applications.

Method

This study aimed to establish the psychometric properties of the WAOMT in a sample of 209 community-dwelling older adults. An independent sample of 27 test-naïve participants were recruited to assess test retest reliability (between 7 and 28 days). Scale psychometric properties were examined using item response theory methods, combined samples (final N = 241). Convergent validity was assessed by comparing performance on the WAOMT with a comprehensive neuropsychological battery of domains (verbal and visual episodic memory, and odor identification), as well as other neuropsychological skills. Based on previous literature, it was predicted that the WAOMT would be positively correlated with conceptually similar cognitive domains.

Results

The WAOMT is a psychometrically sound test with adequate reliability properties and demonstrated convergent validity with tests of verbal and episodic memory and smell identification. Patterns of performance highlight learning and memory characteristics unique to OEM (e.g., learning curves, cued and free recall).

Conclusion

Clinical and research implications include streamlining future versions of the WAOMT to ease patient and administrative burden, and the potential to reliably detect early neuropathological changes in healthy older adults with nonimpaired OEM abilities.

Olfactory Identification in Subjective Cognitive Decline: A Meta-Analysis

BACKGROUND

Recently, subjective cognitive decline (SCD) has been considered to be one of the first signs of Alzheimer's disease (AD). Since this potential early marker is sensitive but not specific to AD, combining it with other markers could ensure higher accuracy when predicting which persons with SCD will convert to AD. Since olfactory dysfunction is observable in both AD and mild cognitive impairment (MCI), it is a promising marker that could help improve the early diagnosis of AD.

OBJECTIVE

The aim of this meta-analysis was to verify whether the presence of SCD is associated with a decrease in olfactory identification ability.

METHODS

We collected articles from the following databases: PsychNet, PubMed, Ebsco, and ProQuest using the keywords: "SCD", "subjective cognitive decline", "subjective cognitive impairment", "subjective memory impairment", "subjective memory decline", "cognitive complaints", "memory complaints", "cognitive concerns", "memory concerns", "olfac*" and "smell". We included articles according to the following criteria: 1) participants aged 50 and over; 2) presence of an SCD group or a conceptual equivalent; 3) presence of a healthy control group with the same age range; and 4) assessment of olfactory identification ability.

RESULTS

Five studies met the inclusion criteria. Small and homogeneous effects were observed for olfactory identification alteration in individuals with SCD relative to controls (g = -0.16, 95% CI [-0.46, 0.14]).

CONCLUSION

Despite the low number of studies included, the findings suggest that odor identification is slightly altered in SCD compared to healthy older adults. This alteration in individuals with SCD could be an early marker of AD.

Olfaction and Aging: A Review of the Current State of Research and Future Directions

Olfaction, the sense of smell, is characterized by a notable age-dependency such that aging individuals are more likely to have poor olfactory abilities. These impairments are considered to be mostly irreversible and as having potentially profound effects on quality of life and food behavior, as well as constituting warning signs of mortality, cognitive dysfunction, and dementia. Here, we review the current state of research on aging and olfaction, focusing on five topics which we regard to be of particular relevance for the field: nutrition and health, cognition and dementia, mortality, environment and genetics, and training-based enhancement. Under each of these headlines, we provide a state-of-the-art overview and discuss gaps in our knowledge which might be filled by further research. Understanding how olfactory abilities are diminished in aging, and how they may be alleviated or recovered, involves a set of challenging tasks for researchers in the years to come.

Olfactory impairment in men and mice related to aging and amyloid-induced pathology

Olfaction, or the sense of smell, is one of the most ancient senses in men and mice, important for a large variety of innate and acquired behaviors. Clinical data reveal an early impairment of olfaction during normal aging and in the course of neurodegenerative diseases, but the underlying cellular/molecular mechanisms remain obscure. In the current review, we compare different aspects of the aging- and Alzheimer's disease related impairment of olfaction in men and mice, aiming at the identification of common morbidities and biomarkers, which can be analyzed in detail in the appropriate mouse models. We also identify common, often interdependent (patho)physiological pathways, including but not limited to extracellular amyloid depositions, neuroinflammation, ɛ4 allele of the apolipoprotein E, CNS insulin resistance, and the impairment of adult neurogenesis, to be targeted by basic and clinical research.

Olfactory Impairment Among Rural-Dwelling Chinese Older Adults: Prevalence and Associations With Demographic, Lifestyle, and Clinical Factors

Objective: Olfactory impairment (OI) refers to decreased (hyposmia) or absent (anosmia) ability to smell. We sought to estimate the prevalence and correlates of OI among rural-dwelling Chinese older adults.

Methods: This population-based cross-sectional analysis included 4,514 participants (age ≥65 years; 56.7% women) from the Multidomain Interventions to Delay Dementia and Disability in Rural China (MIND-China). The 16-item Sniffin' Sticks identification test (SSIT) was used to assess olfactory function. Olfactory impairment was defined as the SSIT score ≤10, hyposmia as SSIT score of 8–10, and anosmia as SSIT score <8. Multivariable logistic regression models were used to examine factors associated with OI.

Results: The overall prevalence was 67.7% for OI, 35.3% for hyposmia, and 32.5% for anosmia. The prevalence increased with age for OI and anosmia, but not for hyposmia. The multivariable-adjusted odds ratio (OR) of OI was 2.10 (95% CI 1.69–2.61) for illiteracy and 1.41 (1.18–1.70) for elementary school (vs. middle school or above), 1.30 (1.01–1.67) for current smoking (vs. never smoking), 0.86 (0.74–0.99) for overweight and 0.73 (0.61–0.87) for obesity (vs. normal weight), 4.21 (2.23–7.94) for dementia, 1.68 (1.23–2.30) for head injury, and 1.44 (1.14–1.83) for sinonasal disease. Illiteracy in combination with either male sex or diabetes was significantly associated with an over two-fold increased OR of OI (p for interactions <0.05).

Conclusion: Olfactory impairment is highly prevalent that affects over two-thirds of rural-dwelling older adults in China. OI is correlated with illiteracy, current smoking, dementia, head injury, and sinonasal disease, but negatively associated with overweight or obesity. Olfactory impairment as a potential clinical marker of neurodegenerative disorders among older adults deserves further investigation.

Serum C-Reactive Protein Is Negatively Associated With Olfactory Identification Ability in Older Adults

IMPORTANCE

Olfactory deficits are common in aging and associated with several conditions linked to inflammation. A few studies suggest that increased concentration of pro-inflammatory biomarkers may be related to olfactory deficits, but these associations are understudied in population-based samples.

OBJECTIVE

To investigate the association between serum concentrations of C-reactive protein (CRP) and olfactory identification level as well as rate of change in aging.

METHODS

We included 1,721 participants (mean age 70.5 years; 61.9% female) with at least two olfactory assessments across the 12-year follow-up. Baseline level and change in odor identification were estimated with linear mixed models as a function of CRP levels, derived from blood plasma at baseline.

RESULTS

Results indicated a negative dose-response association between CRP level and odor identification scores at baseline, after adjustment for demographic, cognitive, health, and lifestyle factors. CRP levels ranging between 11 and 20 mg/L were significantly related to lower olfactory ability (β = -0.811, 95% confidence interval [CI] [-1.503 to -0.118]; p = .022). Likewise, CRP values above 20 mg/L were related to lower olfactory scores, an association that approached statistical significance (β = -0.996, 95% CI [-2.045 to 0.054]; p = .063). We found no associations between CRP and olfactory change (ps > .368). Sensitivity analyses showed that associations between CRP and olfaction were confined to younger participants (age ≤72 years) and men (ps < .034).

CONCLUSIONS

Our findings suggest a negative association between serum CRP levels and olfactory identification ability in aging that may be dependent on age and sex.

Predictors of Olfactory Decline in Aging: A Longitudinal Population-Based Study

BACKGROUND

Olfactory dysfunction is common in aging and associated with dementia and mortality. However, longitudinal studies tracking change in olfactory ability are scarce. We sought to identify predictors of interindividual differences in rate of olfactory identification change in aging.

METHOD

Participants were 1780 individuals, without dementia at baseline and with at least 2 olfactory assessments over 12 years of follow-up (mean age = 70.5 years; 61.9% female), from the Swedish National Study on Aging and Care in Kungsholmen (SNAC-K). Odor identification was assessed with the Sniffin' Sticks. We estimated the impact of demographic, health, and genetic factors on rate of olfactory change with linear mixed effect models.

RESULTS

Advancing age, manufacturing profession, history of cerebrovascular disease, higher cardiovascular disease burden, diabetes, slower walking speed, higher number of medications, and the APOE ε4 allele were associated with accelerated odor identification decline (ps < .014). Multi-adjusted analyses showed unique associations of age, diabetes, and ε4 to olfactory decline (ps < .017). In 1531 participants who remained free of dementia (DSM IV criteria) during follow-up, age, cardiovascular disease burden, and diabetes were associated with accelerated decline (ps < .011). Of these, age and diabetes remained statistically significant in the multi-adjusted model (ps < .001).

CONCLUSION

Demographic, vascular, and genetic factors are linked to rate of decline in odor identification in aging. Although some olfactory loss may be an inevitable part of aging, our results highlight the importance of vascular factors for the integrity of the olfactory system, even in the absence of dementia.

The Association between HbA1c Levels, Olfactory Memory and Cognition in Normal, Pre-Diabetic and Diabetic Persons

BACKGROUND AND AIM

Recent data have shown that olfactory dysfunction is strongly related to Alzheimer's Disease (AD) that is often preceded by olfactory deficits suggesting that olfactory dysfunction might represent an early indicator of future cognitive in prediabetes.

METHODS

We have applied to a group of normal (n=15), prediabetic (n=16) and type 2 diabetic outpatients (n=15) olfactory testing, 1.5-T MRI scanner and detailed cognitive evaluation including the standard Mini-Mental State Examination (MMSE) form, Short Blessed Test (SBT), Letter Fluency Test (LFT) and the category fluency test with animal, Fruit and Vegetable Naming (CFT).

RESULTS

We have shown that Odour Threshold (OT), Discrimination (OD), and Identification (OI) scores and most cognitive test results were significantly different in the prediabetes and diabetes group compared to those in the control group. OD and OT were significantly different between the prediabetes and diabetes group, although the cognitive test results were only significantly different in the prediabetes and diabetes group compared to those in the control group. In evaluating the association between OI, OT, OD scores and specific cognitive tests, we have found, that impaired olfactory identification was the only parameter that correlated significantly with the SBT both in the pre-diabetes and diabetes group. Although spot glucose values were only correlated with OT, HbA1c levels were correlated with OT, OD, and OI, as well as results of the letter fluency test suggesting that HbA1c levels rather than the spot glucose values play a critical role in specific cognitive dysfunction.

CONCLUSION

To the best of our knowledge, this is the first prospective study to demonstrate a strong association between olfactory dysfunction and specific memory impairment in a population with prediabetes and diabetes suggesting that impaired olfactory identification might play an important role as a specific predictor of memory decline.

Western Diet Accelerates the Impairment of Odor-Related Learning and Olfactory Memory in the Mouse

Olfactory dysfunction could be an early indicator of cognitive decline in type 2 diabetes (T2D). However, whether obesity affects olfaction in people with T2D is unclear. This question needs to be addressed, because most people with T2D are obese. Importantly, whether different contributing factors leading to obesity (e.g., different components of diet or gain in weight) affect specific olfactory functions and underlying mechanisms is unknown. We examined whether two T2D-inducing obesogenic diets, one containing a high proportion of fat (HFD) and one with moderate fat and high sugar (Western diet, WD), affect odor detection/discrimination, odor-related learning, and olfactory memory in the mouse. We also investigated whether the diets impair adult neurogenesis, GABAergic interneurons, and neuroblasts in the olfactory system. Here, we further assessed olfactory cortex volume and cFos expression-based neuronal activity. The WD-fed mice showed declined odor-related learning and olfactory memory already after 3 months of diet intake (p = 0.046), although both diets induced similar hyperglycemia and weight gain compared to those of standard diet-fed mice (p = 0.0001 and p < 0.0001, respectively) at this time point. Eight months of HFD and WD diminished odor detection (p = 0.016 and p = 0.045, respectively), odor-related learning (p = 0.015 and p = 0.049, respectively), and olfactory memory. We observed no changes in the investigated cellular mechanisms. We show that the early deterioration of olfactory parameters related to learning and memory is associated with a high content of sugar in the diet rather than with hyperglycemia or weight gain. This finding could be exploited for understanding, and potentially preventing, cognitive decline/dementia in people with T2D. The mechanisms behind this finding remain to be elucidated.

Olfactory Memory in Depression: State and Trait Differences between Bipolar and Unipolar Disorders

Background: Changes in olfactory recognition memory may constitute sensory markers in depression. Significant differences may exist between unipolar and bipolar depression. Our study compares olfactory memory between control, unipolar, and bipolar patients in depressed and euthymic states in order to identify potential markers of depression. Methods: 176 participants were recruited in 5 groups: depressed bipolar (DB), euthymic bipolar (EB), depressed unipolar (DU), euthymic unipolar (EU), and controls (HC). The participants had a standardized clinical and olfactory assessment (olfactory memory, evaluation of pleasantness, intensity, familiarity, and emotional aspect of smells). Results: DU, DB, and EU patients had a deficit in olfactory memory compared to HC. DB patients had lower capacity to recognize new odors. DB and DU patients had more limited detection of unfamiliar odors than HC. DB patients rated odors as less pleasant compared to the other groups. All groups had lower hedonic ratings than HC. DB patients had lower emotional ratings than EU patients. Conclusions: Olfactory memory is impaired in depressive states, thus constituting a state marker of depression. Impairments in olfactory memory persist after remission of bipolar depression, thus constituting a possible trait marker of bipolarity. Hedonic rating differentiates unipolar from bipolar depression. This is the first study that identifies a sensory marker differentiating between unipolar and bipolar depression.

Did Proust predict the existence of episodic memory?

Cognitive psychologists have often discussed the idea that when Proust used in his books the concept of involuntary memories, which could be retrieved by an odor or a taste, he was in fact predating the notion of modern episodic memory. Since the publication of his famous "In Search of Lost Time", considerable progress has been made on our understanding of various types of memory and of the mechanisms involved in different brain circuits and synapses responsible for their long-term storage. This review will focus on the role of hippocampus in episodic memory, including its role in encoding time and various elements of episodes, in particular olfactory information. Our conclusion is that Proust did indeed predict the existence of episodic memory, although he did not realize that, in addition to remembering things past, memory is also used to predict the future.

Subjective Olfactory Loss in Older Adults Concurs with Long-Term Odor Identification Decline

Olfactory impairments may provide early indications of future health outcomes in older adults. Thus, an important question concerns whether these impairments can be self-assessed. Previous findings of cross-sectional studies indicate low correlations between self-reported olfactory function and objective olfactory performance. On the other hand, subjective olfactory impairments predict future dementia and mortality in longitudinal settings. No previous study has assessed the relationship between subjectively and objectively measured decline in olfaction over time. Based on data for 903 older adults derived from the Betula Study, a Swedish population-based prospective study, we tested whether rate-of-change in odor identification could be predicted from subjective olfactory decline over a time span of 10 years during which subjective and objective odor functions were assessed on 2 or 3 test occasions. Indeed, we found that participants who experienced subjective olfactory decline over the study period also had significantly steeper rates of decline in odor identification, even after adjusting for demographic, cognitive, and genetic factors that previously have been associated with performance in odor identification. This association was, however, not present in a subsample with baseline cognitive impairment. We interpret these results as evidence that when asked about whether they have an olfactory impairment or not, older persons are assessing intraindividual olfactory changes, rather than interindividual differences. Our results indicate that subjective olfactory loss reflects objective olfactory decline in cognitively intact older adults. This association might be harnessed to predict health outcomes and highlights the need to develop effective olfactory self-assessments.

Temporolimbic cortical volume is associated with semantic odor memory performance in aging

Olfactory function, and specifically semantic olfactory memory (i.e., odor identification), has frequently been shown to predict cognitive functioning across multiple domains in old age. This observation suggests that olfactory function can serve as a marker for the integrity of temporolimbic cortical networks, but a clear delineation of this association is still missing. To address this issue, the present study employed voxel-based morphometry in a region of interest-based design to determine the extent to which gray matter volumes of core olfactory and memory areas are associated with olfactory memory performance in an aging population free from neurodegenerative disease. We further aimed to determine potential overlap in structural anatomical correlates, and differences in association strength, for semantic and episodic olfactory memory. Structural magnetic resonance imaging (MRI), episodic and semantic odor memory and episodic and semantic verbal memory data were collected in 422 participants from the Swedish National Study on Aging and Care in Kungsholmen (SNAC-K), all aged ​≥ ​60 years. Controlling for age and education, semantic, but not episodic, olfactory memory was positively related to gray matter volume in a cluster extending from the anterior hippocampus and amygdala into the posterior piriform cortex. The observed associations remained even when verbal memory performance was controlled for, supporting a link between the olfactory memory domain and cortical volume over and above more generalized memory abilities. As such, our data provide evidence for distinct functional-structural associations for semantic odor memory, supporting the idea of temporolimbic integrity as a neurobiological substrate linking olfactory function to cognitive health in old age.

Interaction Between Odor Identification Deficit and APOE4 Predicts 6-Year Cognitive Decline in Elderly Individuals

Olfactory identification impairment might indicate future cognitive decline in elderly individuals. An unresolved question is to what extent this effect is dependent on the ApoE-ε4, a genotype associated with risk of Alzheimer's Disease (AD). Given the current concern about reproducibility in empirical research, we assessed this issue in a large sample (n = 1637) of older adults (60 - 96 years) from the population-based longitudinal Swedish National Study on Aging and Care in Kungsholmen (SNAC-K). A hierarchical regression analysis was carried out to determine if a low score on an odor identification test, and the presence of ApoE-ε4, would predict the magnitude of a prospective 6-year change in the Mini-Mental State Examination (MMSE) after controlling for demographic, health-related, and cognitive variables. We found that overall, lower odor identification performance was predictive of cognitive decline, and, as hypothesized, we found that the effect was most pronounced among ApoE-ε4 carriers. Our results from this high-powered sample suggest that in elderly carriers of the ApoE-ε4 allele, odor identification impairment provides an indication of future cognitive decline, which has relevance for the prognosis of AD.

Contrasting olfaction, vision, and audition as predictors of cognitive change and impairment in non-demented older adults

OBJECTIVE

This study examines the relative utility of a particular class of noninvasive functional biomarkers-sensory functions-for detecting those at risk of cognitive decline and impairment. Three central research objectives were examined including whether (a) olfactory function, vision, and audition exhibited significant longitudinal declines in nondemented older adults; (b) multiwave change for these sensory function indicators predicted risk of mild cognitive impairment (MCI); and (c) change within persons for each sensory measure shared dynamic time-varying associations with within-person change in cognitive functioning.

METHOD

A longitudinal sample (n = 408) from the Victoria Longitudinal Study was assembled. Three cognitive status subgroups were identified: not impaired cognitively, single-assessment MCI, and multiple-assessment MCI.

RESULTS

We tested independent predictive associations, contrasting change in sensory function as predictors of cognitive decline and impairment, utilizing both linear mixed models and logistic regression analysis. Olfaction and, to a lesser extent, vision were identified as the most robust predictors of cognitive status and decline; audition showed little predictive influence.

CONCLUSIONS

These findings underscore the potential utility of deficits in olfactory function, in particular, as an early marker of age- and pathology-related cognitive decline. Functional biomarkers may represent potential candidates for use in the early stages of a multistep screening approach for detecting those at risk of cognitive impairment, as well as for targeted intervention. (PsycINFO Database Record

Effect of Worry Level on Recall Memory for Odors in ApoE-ε4 Carriers and Non-Carriers

OBJECTIVE

Increased levels of worry, age, and presence of the apolipoprotein-E (ApoE)-ε4 allele are associated with the risk of developing cognitive declines and Alzheimer's disease (AD). Odor memory performance has been shown to vary as a function of age and ApoE genotype, and odor memory tests are sensitive to preclinical AD. Worry is known to influence verbal memory; however, its effects on odor memory are unknown. This study aimed to assess the relationships between worry, age, and ε4 status on odor memory.

METHOD

Worry was evaluated for young (n = 53) and older (n = 45) adults using the Penn State Worry Questionnaire. Odor memory was assessed using the California Odor Learning Test, an olfactory analogue to the California Verbal Learning Test.

RESULTS

A significant main effect of worry on long-delay free recall was found, such that increasing worry was associated with better recall across age and ε4 status. A significant interaction effect between ε4 status and worry on both short-and long-delay cued recall was found, such that across age, higher worry was associated with increased cued recall scores among ε4-negative adults, and decreased scores among ε4-positive adults.

CONCLUSIONS

Findings demonstrated that worry influences odor memory and exerts a particular effect on cued recall among ε4 carriers who are at a greater risk of developing AD. Worry is a modifiable predictor of cognitive decline and risk of dementia in aging. Future studies on the effects of treatments aimed at reducing worry (e.g., cognitive behavioral therapies for anxiety) on changes in cognitive functioning are warranted.

Type 2 diabetes impairs odour detection, olfactory memory and olfactory neuroplasticity; effects partly reversed by the DPP-4 inhibitor Linagliptin

Recent data suggest that olfactory deficits could represent an early marker and a pathogenic mechanism at the basis of cognitive decline in type 2 diabetes (T2D). However, research is needed to further characterize olfactory deficits in diabetes, their relation to cognitive decline and underlying mechanisms.

The aim of this study was to determine whether T2D impairs odour detection, olfactory memory as well as neuroplasticity in two major brain areas responsible for olfaction and odour coding: the main olfactory bulb (MOB) and the piriform cortex (PC), respectively. Dipeptidyl peptidase-4 inhibitors (DPP-4i) are clinically used T2D drugs exerting also beneficial effects in the brain. Therefore, we aimed to determine whether DPP-4i could reverse the potentially detrimental effects of T2D on the olfactory system.

Non-diabetic Wistar and T2D Goto-Kakizaki rats, untreated or treated for 16 weeks with the DPP-4i linagliptin, were employed. Odour detection and olfactory memory were assessed by using the block, the habituation-dishabituation and the buried pellet tests. We assessed neuroplasticity in the MOB by quantifying adult neurogenesis and GABAergic inhibitory interneurons positive for calbindin, parvalbumin and carletinin. In the PC, neuroplasticity was assessed by quantifying the same populations of interneurons and a newly identified form of olfactory neuroplasticity mediated by post-mitotic doublecortin (DCX) + immature neurons.

We show that T2D dramatically reduced odour detection and olfactory memory. Moreover, T2D decreased neurogenesis in the MOB, impaired the differentiation of DCX+ immature neurons in the PC and altered GABAergic interneurons protein expression in both olfactory areas. DPP-4i did not improve odour detection and olfactory memory. However, it normalized T2D-induced effects on neuroplasticity.

The results provide new knowledge on the detrimental effects of T2D on the olfactory system. This knowledge could constitute essentials for understanding the interplay between T2D and cognitive decline and for designing effective preventive therapies.

Prevalence and Correlates of Olfactory Dysfunction in Old Age: A Population-Based Study

Background:

Olfactory dysfunction (OD) in old age is associated with poor health outcomes. Interrelationships among different correlates of OD can offer insights into the underlying mechanisms, but to date remain understudied.

Methods:

Odor identification performance and self-reported olfactory functioning were studied in 2,234 people aged 60–90 years, who were free of neurodegenerative disease and enrolled in the Swedish National Study on Aging and Care in Kungsholmen (SNAC-K) study, Stockholm, Sweden. OD was defined as the inability to identify more than 10 out of 16 odors (free or cued identification) in a standardized odor identification task. OD prevalence was estimated, and associations with demographic, genetic, vascular, clinical, and behavioral factors, as well as their interactions were examined using multiple logistic regression analyses.

Results:

Overall prevalence of OD was 24.8% (CI: 23.1; 26.6). Self-reports were characterized by low sensitivity (35%), but high specificity (87%). Advancing age (OR = 15.50, CI = 9.40; 26.10 between the first and last age group), and history of coronary heart disease (OR = 1.35, 95% CI = 1.04; 1.75) were the principal factors associated with an increased probability of OD, whereas female gender (OR = 0.53, 95% CI = 0.43; 0.66) and more years of education (OR = 0.97, CI 0.94; 0.99) were linked to a lower probability. Exploratory interaction analyses indicated that prevalence of OD was particularly elevated among Apolipropotein E (APOE) ε4 allele carriers who were also obese, and that being physically active counteracted the negative impact of cerebrovascular disease on OD.

Conclusion:

Demographic and genetic factors, but also prior and current health insults, are linked to OD in old age. Modulatory effects of behavioral factors highlight their value as possible prevention targets.

Phantom Smells: Prevalence and Correlates in a Population-Based Sample of Older Adults

Loss of olfactory function is common in old age, but evidence regarding qualitative olfactory dysfunction in the general older population is scarce. The current study investigates the prevalence and correlates of phantom smell experiences (phantosmia) in a population-based study (Swedish National Study on Aging and Care in Kungsholmen [SNAC-K]) of Swedish adults (n = 2569) aged between 60 and 90 years. Phantosmia was assessed through a standardized interview and defined as reporting having experienced an odor percept in the absence of any stimuli in the surrounding environment that could emit the odor. The relationships between phantosmia and demographic, genetic, health-related, and behavioral variables were analyzed with hierarchical logistic regression analyses. The overall prevalence of phantom smells was 4.9%, and was associated with female gender, carrying the met allele of the BDNF gene, higher vascular risk burden, and reporting distorted smell sensations (parosmia). Olfactory dysfunction was, however, not related to phantosmia. The most frequently reported phantom smell was smoky/burnt. A novel finding was that some individuals reported phantom smells with an autobiographical connotation. The results from this study indicate that the prevalence of phantosmia in the general older population is not negligible and that some factors that are beneficial for preserved olfactory function, such as female gender and the BDNF met allele, are also associated with the occurrence of phantom smells.

APOE-ɛ4 effects on longitudinal decline in olfactory and non-olfactory cognitive abilities in middle-aged and old adults

Characterizing aging-related decline trajectories in mental abilities, and relationships of the ɛ4 allele of the Apolipoprotein gene, helps to identify individuals at high risk for dementia. However, longitudinal changes in olfactory and non-olfactory cognitive abilities have not been investigated in relation to the ɛ4 allele. In the present study, participants from a large population-based study (657 middle-aged and 556 old) were tested over 10 years on their performance on an odor identification task and three non-olfactory cognitive tasks; MMSE, episodic memory, and semantic memory. Our key finding is that in middle-aged participants, odor identification declined twice as fast for ɛ4/4 homozygotes, compared to non-carriers. However, in old participants, the ɛ4/4 homozygotes showed an impaired odor identification ability, but they declined at a similar rate as the non-carriers. Furthermore, in old participants all assessments displayed aging-related declines, but exaggerated declines in ɛ4-carriers were found only in MMSE and episodic memory assessments. In sum, we present evidence that odor identification ability starts to decline already in middle-aged, and that carriers of ɛ4/4, who are at highest risk of developing dementia, decline twice as fast. Our results may have implications for use of odor identification assessment in detection of early-stage dementia.

Olfactory Functions in Adults With Autism Spectrum Disorders

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