Steven Nordin

Odor identification as an early marker for Alzheimer's disease: Impact of lexical functioning and detection sensitivity

The impact of lexical functioning and detection sensitivity on the deficit of odor identification in Alzheimers disease (AD) was studied in persons diagnosed with probable and questionable AD. Tests consisted of lexical-based odor identification, lexical-based picture identification, picture-based odor identification, and odor-detection threshold. Results suggest (1) that odor identification is poorer than picture identification in probable and questionable AD, (2) that odor identification continues to be poor even when lexical demands are eliminated, (3) that odor detection does contribute to the odor-identification deficit, but does not account for it completely, and (4) that odor identification tests have a correct classification rate of 83-100%. Odor identification tests can be very useful tools in diagnosing AD and should be considered an important addition to existing diagnostic test batteries.

Olfactory event-related potentials and aging: normative data.

Unlike the clinical usages of evoked potentials (e.g. brain stem auditory evoked potentials for the assessment of auditory function), normative data for the olfactory event-related potential (OERP) have been unavailable. The principal objective was to establish normative data across the human life span for OERPs with a given set of parameters. Participants were 140 persons from seven age groups (16-19, 20-29, 30-39, 40-49, 50-59, 60-69 and 70-79 years of age), with equal numbers of males and females, screened for nasal health and dementia. The odor stimulus was amyl acetate, presented at nasal temperature in a humidified airstream delivered by an air-dilution olfactometer at a constant flow rate, using a 60-s inter-stimulus interval. OERPs were recorded at Fz, Cz, and Pz electrode sites, amplified and averaged over trials. Amplitudes of the N1/P2 and P3 and latencies of the P2 and P3 were analyzed. Processing speed decreased at a constant rate over decades for the sensory (P2 latency) as well as cognitive (P3 latency) components. Decline in amplitude over decades was also apparent. Normative data will be useful in research on olfactory function and in clinical assessment of olfactory functional status.

Odor learning, recall, and recognition memory in young and elderly adults.

use of an odor learning test and the California Verbal Learning Test in young and elderly adults enabled comparison of age-related effects on recall and recognition memory. Assessment of odor identification further enabled study of which odor function (recall, identification, recognition) is most affected by aging, the odor functions interrelationships, and predictors of odor recall. Results suggested that both recall and recognition were significantly affected by aging and that the odor-recall decline cannot simply be referred to poor identification. Very similar age-related effect sizes were found for the 3 types of odor functions. Finally, the combined ability to encode, store, and retrieve odors appears to predict overall recall performance (including its identification component) better than do identification and recognition.

Odor Memory in Normal Aging and Alzheimer's Diseasea

ABSTRACT: The ability in normal elderly to verbally recall previously presented odors and to learn this task across trials was studied by applying a design which compared performance on the California Verbal Learning Test (CVLT) with an analogous odor test. Results suggest that both immediate and delayed recall of odors, both free and cued, as well as the ability to learn across trials is impaired in normal aging, perhaps more so for olfaction than for audition, which can be referred to poor use of semantic‐clustering strategies and poor identification. Olfactory decline in memory in normal aging is, however, far from as affected as in Alzheimers disease (AD). Two studies of persons with questionable AD demonstrated significant deficits in both recognition memory and identification of odors. Although further research is required, the findings from these preclinical cases imply that performance on olfactory‐mediated tasks may contribute to early diagnosis of AD.

Prevalence and Assessment of Qualitative Olfactory Dysfunction in Different Age Groups

The prevalence of parosmia and phantosmia among 363 chemosensory and nasal/sinus patients was studied, as was the accuracy with which our clinical questionnaire could assess these dysfunctions. We then investigated whether patients with parosmia or phantosmia, matched for odor intensity, perform poorer on odor identification than do patients with no dysosmia. More than 40% of the study group evidenced either parosmia (18.7%) and/or phantosmia (25.6%), a finding that suggests that more attention should be paid by the medical practitioner in addressing qualitative olfactory dysfunction. Furthermore, it appears that assessment of these dysfunctions may aid in differential diagnosis, and that questionnaires can be used with reasonable validity irrespective of the patients age. Finally, the results imply that parosmia may be reflected in a discrepancy between odor identification and detection.

Odor identification impairment in carriers of ApoE-ɛ4 is independent of clinical dementia

The ApoE gene is expressed in olfactory brain structures and is believed to play a role in neuronal regenerative processes as well as in development of Alzheimers disease (AD), the most common form of dementia. The varepsilon4 allele has been reported to be associated with compromised odor identification ability in the elderly, and this deficit has been interpreted as a sign of pre-diagnostic AD. However, because it has not been demonstrated that the relationship between the varepsilon4 allele and odor identification is mediated by dementia, it is possible that the varepsilon4 allele may have an effect on odor identification over and above any effects of dementia. The present study investigated effects of ApoE-status on odor identification in a large, population-based sample (n=1236) of adults (45-80 years), who were assessed for dementia at time of testing and 5 years later. The results showed that the varepsilon4 allele was associated with an odor identification deficit among elderly participants (75-80). Critically, this effect remained after current and pre-diagnostic dementia, vocabulary, global cognitive status and health variables were partialled out. The present results suggest that the ApoE gene plays a role in olfactory functioning that is independent of dementia conversion within 5 years.

Substance and tongue-region specific loss in basic taste-quality identification in elderly adults

Physiological anorexia, decreased dietary variation, and weight loss associated with poor health are common conditions in the elderly population, with changes in chemosensory perception as important contributing causes. The present study of age-related taste loss aimed to investigate the question whether this loss is generalised and unspecific, or whether it exhibits differences in relation to certain tastants and/or differences in the topographical distribution of age-related loss. Impregnated “taste strips” with four concentrations of each of the tastants sucrose, NaCl, quinine-hydrochloride, and citric acid were applied on the tip, midlateral and posteromedial tongue regions to be identified as either sweet, salty, bitter, or sour by 30 young and 26 elderly adults. The results showed more pronounced age-related loss in identification for citric acid and quinine-hydrochloride than for sucrose and NaCl at both the tip and midlateral regions, but not at the posteromedial region where both age groups performed close to chance level. These findings may have implications for food preferences, and thus, the diets of elderly people.

Odor Identification Deficit as a Predictor of Five-Year Global Cognitive Change: Interactive Effects with Age and ApoE-ε4

Olfactory impairments are present in common neurodegenerative disorders and predict conversion to dementia in non-demented individuals with cognitive impairment. In cognitively intact elderly, evidence is sparse regarding the role of olfactory deficits in predicting cognitive impairment. The present study investigated predictors of 5-year prospective decline in the Mini-Mental State Examination (MMSE) in a large (nxa0=xa0501), population-based sample of elderly (65–90xa0years) individuals. All participants were genotyped for the ApoE gene, assessed for health factors, and were non-demented at the baseline assessment. After partialling out the influences of demographic and health-factors at baseline and dementia at follow-up, poor odor identification ability in combination with older age and the ApoE-ε4 allele predicted larger prospective global cognitive decline. This effect could not be produced by a vocabulary test. In sum, the findings suggest that an olfactory deficit can dissociate between benign and malign global cognitive development in non-demented, very old ε4-carriers, who are at high risk of developing dementia.

Age-associated increases in intensity discrimination for taste.

Impaired taste sensation in the aging person may affect the appreciation of food and beverages and compromise nutritional status. Changes in flavor perception may be due to altered ability to discriminate between intensities of suprathreshold taste stimuli. An interesting question is whether all taste qualities (sweet, salty, sour, bitter) show similar age-associated decline in intensity discrimination. Taste intensity discrimination has been shown to be significantly poorer in elderly than in young women for the bitter stimulus caffeine, but not for the sweet stimulus sucrose. The present experiment investigated effects of taste substance and age on taste intensity discrimination by assessing Weber ratios (WRs) for citric acid and sodium chloride (NaCl) in 60 people, half elderly, and half women. Results indicate a significant effect of age on WRs for citric acid and NaCl, suggesting the importance of suprathreshold intensity discrimination for taste perception in the elderly.

Circadian rhythm and desensitization in chemosensory event-related potentials in response to odorous and painful stimuli

Olfactory (H2S) and trigeminal (CO2) event-related potentials (ERPs) were studied with respect to circadian rhythm and desensitization. ERPs, perceived odor and pain intensity, oral temperature, blood pressure, heart rate, nasal volume, and sleepiness were assessed four times at 04:00, 08:00, 12:00, 16:00, 20:00, and 24:00 hr in five young men. For each of these 24 sessions per participant, H2S and CO2 were each presented in 15 series of five stimuli with a 5-s ISI within and 30-s ISI between series. ERP amplitudes, but not latencies, followed a circadian rhythm (largest at 16:00 and smallest at 04:00) similar to oral temperature and opposite to sleepiness. Amplitudes decreased (most pronounced at 16:00 and 20:00) and latencies increased with repeated stimulation, suggesting desensitization, in accordance with odor and pain intensity. These findings imply that circadian rhythm and desensitization should be considered in chemosensory ERP studies.