Perceived intensity of odor as a function of time of adaptation

Effect of olfactory stimulation from aromatherapy on the autonomic nervous activity during aerobic exercises

Variations in the autonomic nervous system activity during exercise therapy in patients with cardiovascular diseases may lead to adverse events. Aromatherapy may reduce these adverse events by enhancing parasympathetic nervous activity (PNA). However, the effects of aromatherapy during exercise remain relatively unknown. This study aimed to evaluate the effect of aromatherapy on autonomic nervous activity during exercise and recovery. This randomized crossover study included 20 healthy men subjected to both aroma and placebo conditions which involved rest and moderate-intensity aerobic exercise on a cycle ergometer, followed by recovery. Blood pressure, heart rate variability indices, and SpO2 were measured during the rest, exercise, and recovery phases. Moreover, aroma preferences and emotional changes in response to the aroma were assessed. Under the placebo condition, high frequency (HF), root mean square of successive differences indices, and heart rate showed delayed recovery (P < 0.05). Furthermore, a moderate positive correlation was identified between aroma preference, pleasant emotions induced by aromatherapy, and the HF index (P < 0.05). These results indicate that aromatherapy facilitates the recovery of PNA after exercise. Furthermore, these effects were more pronounced among individuals who exhibited a stronger preference for and more positive emotions toward aromas.

Orthonasal olfactory influences on consumer food behaviour

It is often suggested in the popular press that food chains deliberately introduce enticing product aromas into (and in the immediate vicinity of) their premises in order to attract customers. However, despite the widespread use of odours in the field of sensory marketing, laboratory research suggests that their effectiveness in modulating people's food behaviours depends on a range of contextual factors. Given the evidence that has been published to date, only under a subset of conditions is there likely to be a measurable effect of the presence of ambient odours on people's food attitudes and choices. This narrative historical review summarizes the various ways in which food odours appear to bias people's food preferences (appetite) and food choices (food consumption and purchase). Emphasis is placed on those experimental studies that have been designed to investigate how the characteristics of the olfactory stimuli (e.g., the congruency between the olfactory cues and the foods, intensity and duration of exposure to odours, and taste properties of odours) modulate the effects of olfactory cues on food behaviour. The review also explores the moderating roles of individual differences, such as dietary restraint, Body Mass Index (BMI), genetic and cultural differences in odour sensitivity and perception. Ultimately, following a review of empirical studies on food-related olfaction, current approaches in scent marketing are discussed and a research agenda is proposed to help encourage further studies on the effective application of scents in promoting healthy foods.

Abnormal visual and olfactory sensations during radiation therapy: a prospective study

PURPOSE

Patients sometimes report phosphene and phantosmia during radiation therapy (RT). However, the detail features and related factors are not well understood. Our prospective study aimed to investigate the characteristics of phantosmias and phosphenes, to identify factors that influence the occurrence, intensity and hedonic (pleasantness/unpleasantness) ratings of such sensations during RT.

METHODS

We included a total of 106 patients (37 women), who underwent RT in regions of the brain, ear, nose, throat (ENT), and other areas of the body for a duration of 43 ± 5 days. Medical history and treatment parameters were collected in a structured medical interview. Olfactory function was measured using the Sniffin' Stick Odor Identification Test at baseline. Phantosmia and phosphene were recorded weekly based on a self-report questionnaire.

RESULTS

There were 37% of the patients experiencing phantosmias, 51% experiencing phosphenes, and 29% simultaneously experiencing both sensations. Phosphenes were typically perceived as a flashily blue, white and/or purple light, phantosmias were typically perceived as a chemical-like, metallic or burnt smell. Younger age (F = 7.81, p < 0.01), radiation in the brain region (χ2 = 14.05, p = 0.02), absence of taste problems (χ2 = 10.28, p = 0.01), and proton RT (χ2 = 10.57, p = 0.01) were related to these abnormal sensations. History of chemical/dust exposure predicted lower intensity (B = -1.52, p = 0.02) and lower unpleasantness (B = 0.49, p = 0.03) of phantosmia. In contrast, disease (tumor) duration (B = 0.11, p < 0.01), food allergy (B = 2.77, p < 0.01), and epilepsy (B = -1.50, p = 0.02) influence phosphenes intensity. Analgesics intake predicted a higher pleasantness of the phosphenes (B = 0.47, p < 0.01).

CONCLUSIONS

Phantosmias and phosphenes are common during RT. The treatment settings and individual arousal level influence the occurrence, intensity and hedonic of such abnormal sensations. Phantosmias and phosphenes may involve more central neural than peripheral mechanism, and they could be elicited with activation of areas that are not regarded to be part of the olfactory or visual network.

Olfactory adaptation: recordings from the human olfactory epithelium

Purpose

Olfactory adaptation is a peripheral (at the epithelium level) or a central (at the brain level) mechanism resulting from repeated or prolonged odorous exposure that can induce a perceptual decrease. The aim of this study was to assess whether a peripheral adaptation occurs when an odor is repeated ten times. Moreover, the specificity of the peripheral adaptation to the nature of the odorant was investigated.

Methods

Four odorants (eugenol, manzanate, ISO E Super and phenylethanol) were presented using precisely controlled air-dilution olfactometry. They differed in terms of their physicochemical properties. Electrophysiological recordings were made at the level of the olfactory mucosa, the so-called electro-olfactogram (EOG). Thirty-five right-handed participants were recruited.

Results

Sixty-nine percent of the participants presented at least one EOG, whatever the odor condition. The EOG amplitude did not significantly decrease over 10 repeated exposures to any odorant. The intensity ratings tended to decrease over stimulations for manzanate, PEA, and eugenol. No correlation was found between the mean EOG amplitudes and the mean intensity ratings. However, the presence of EOG amplitude decreases over stimulations for few subjects suggests that peripheral adaptation might exist.

Conclusion

Overall, our results did not establish a clear peripheral adaptation measured with EOG but indicate the eventuality of such an effect.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00405-021-07170-0.

Older and Young Adults Experience Similar Long-Term Olfactory Habituation

Olfactory habituation corresponds to a decreased behavioral or perceptual response to an odor after a prolonged exposure to this odor. Our aim was to investigate whether long-term olfactory habituation and its recovery are similar in young (<35 years old) and older adults (>50). Fifty-seven participants were recruited for a 5-week longitudinal study. They were exposed to one of the two odors (manzanate alpha [MA], irone alpha [IA]) for 2 weeks at home. Olfactory detection thresholds for both odors were measured before and after exposure. Results showed that the two age groups behaved similarly. The long-term exposure to an odor led to a temporary increase of its detection threshold (lower sensitivity to the odor). IA thresholds were more sensitive to the duration of exposure with the odor than MA thresholds. One week after termination of exposure, participants fully recovered and even became more sensitive to both odors. No cross-habituation was found between the two odors. Our findings highlight that long-term habituation is specific to the odor exposed, behaves the same in young and older adults, and is fully reversible in both age groups after 1 week.

Olfactory Cues of Restaurant Wait Staff Modulate Patrons' Dining Experiences and Behavior

Ambient scents at retail stores have been found to modulate customer perceptions and attitudes toward retail products and stores. Although ambient scent effects have also been observed in restaurant settings, little is known about the scent-related influences of restaurant wait staff on patron perception and behavior. This study aimed to determine whether olfactory cues from restaurant wait staff can affect patrons’ dining experiences and interpersonal behavior with respect to menu choice, flavor perception, overall liking of meal items, meal satisfaction, consumption amount, and tip amount for wait staff. A total of 213 adults with no olfactory impairments were asked to select and consume one of four chicken meat menu items: baked, broiled, fried, and smoked chicken, in a mock restaurant setting, under one of the three most likely scents of wait staff: congruent (smoky barbecue scent), fragrance (perfume scent), and no scent (control) applied to fabric aprons of wait staff. The results showed that menu choice and flavor perception of chicken meat items did not differ in the presence of the three scent conditions. The effects of wait staff scents on overall liking of chicken meat items, meal satisfaction, and tip amount for wait staff were found to differ as a function of patron gender. Female patrons gave higher ratings of overall liking and meal satisfaction under the fragrance scent condition than under the no scent condition, while male patrons showed no effect with respect to overall liking and an opposite result in the meal satisfaction. Female patrons gave larger tips to wait staff under the congruent scent condition than under the no scent condition, while male patrons exhibited no effect. Patrons also were found to consume chicken meat items the least under the congruent scent condition. In conclusion, this study provides new empirical evidence that wait staff scents at restaurants can affect patrons’ dining experiences and interpersonal behavior and that the effects of such scents vary as a function of patron gender.

Short or long runs: An exploratory study of odor-induced fMRI design

OBJECTIVE

Functional magnetic resonance imaging (fMRI) is a non-invasive neuroimaging technique widely used in olfactory research. During a typical fMRI olfactory block-design, one functional "run" refers to a combination of multiple blocks with continuous brain image acquisition. The current study investigated the length of functional runs on odor-induced brain response signals (blood oxygen level dependent [BLOD]) within the primary and key secondary olfactory areas.

METHODS

Twenty-five female adults (age range 19 to 30 years, mean age 25 years) underwent a block-design fMRI measurement with odor stimulation. Twelve participants received the odor stimuli within a short run paradigm (six blocks in each 4-minute run, eight runs in total), and 13 participants received the odor stimulation with a long-run paradigm (12 blocks in each 8-minute run, four runs in total). For each paradigm, two odors (peach and rose) were alternatingly presented between runs. Participants rated odor intensity and pleasantness at the end of each run. Ratings and fMRI data were analyzed for different subsections and compared between groups.

RESULTS

There was a higher level of brain activation in the insula and orbitofrontal cortex during the short-run paradigm as compared to the long-run paradigm. However, there was no difference for odor intensity or pleasantness ratings.

CONCLUSION

The current study suggested the employment of short runs with multiple repetitions for odor stimulation during fMRI research.

LEVEL OF EVIDENCE

3 Laryngoscope, 130:1110-1115, 2020.

Associations Between Vision, Hearing, and Olfactory Impairment With Handgrip Strength

Objectives: We aimed to assess the cross-sectional associations between sensory impairments (vision, hearing, and/or olfactory loss) and handgrip strength. Method: In the Blue Mountains Eye Study, 947 participants aged 65+ years had handgrip strength measured using a dynamometer. Visual impairment was defined as visual acuity <20/40 (better eye), and hearing impairment as average pure-tone air conduction threshold >25 dBHL (500-4,000 Hz). Olfaction was measured using the San Diego Odor Identification Test. Results: Marginally significant associations between sensory impairment and handgrip strength were observed after multivariable adjustment. For example, women with two or three sensory impairments had lower adjusted mean handgrip strength (17.47 ± 0.5 kg) versus women who had no sensory loss (18.59 ± 0.3 kg; p = .06) or only one sensory impairment (18.58 ± 0.3 kg; p = .05), respectively. No significant associations were observed in men. Discussion: Women who had multiple sensory impairments had reduced muscle strength as indicated by ~1.1 kg lower mean handgrip strength.

Attentional modulation of desensitization to odor

Subjective and behavioral responsiveness to odor diminishes during prolonged exposure. The precise mechanisms underlying olfactory desensitization are not fully understood, but previous studies indicate that the phenomenon may be modulated by central-cognitive processes. The present study investigated the effect of attention on perceived intensity during exposure to a pleasant odor. A within-subjects design was utilized with 19 participants attending 2 sessions. During each session, participants continuously rated their perceived intensity of a 10-minute exposure to a pleasant fragrance administered using an olfactometer. An auditory oddball task was implemented to manipulate the focus of attention in each session. Participants were instructed to either direct their attention toward the sounds, but still to rate odor, or to focus entirely on rating the odor. Analysis revealed three 50-second time windows with significantly lower mean intensity ratings during the distraction condition. Curve fitting of the data disclosed a linear function of desensitization in the focused attention condition compared with an exponential decay function during distraction condition, indicating an increased rate of initial desensitization when attention is distracted away from the odor. In the focused-attention condition, perceived intensity demonstrated a regular pattern of odor sensitivity occurring at approximately 1−2 minutes intervals following initial desensitization. Spectral analysis of low-frequency oscillations confirmed the presence of augmented spectral power in this frequency range during focused relative to distracted conditions. The findings demonstrate for the first time modulation of odor desensitization specifically by attentional factors, exemplifying the relevance of top-down control for ongoing perception of odor.

Taste Perception and Caffeine Consumption: An fMRI Study

Caffeine is ubiquitous, yet its impact on central taste processing is not well understood. Although there has been considerable research on caffeine’s physiological and cognitive effects, there is a paucity of research investigating the effects of caffeine on taste. Here we used functional magnetic resonance imaging (fMRI) to investigate group differences between caffeine consumers and non-consumers in blood-oxygenation-level-dependent (BOLD) activation during hedonic evaluation of taste. We scanned 14 caffeine consumers and 14 caffeine non-consumers at 3 Tesla, while they rated three tastes: caffeine (bitter), sucrose (sweet), and saccharin (sweet with bitter after taste), in aqueous solutions. Differences in BOLD activation were analyzed using voxel wise independent samples t-tests within Analysis of Functional Neuroimage (AFNI). Results indicated that during the hedonic evaluation of caffeine or sucrose, caffeine non-consumers had significantly greater activation in neuronal areas associated with memory and reward. During the hedonic evaluation of saccharin, caffeine consumers had significantly greater activation in areas associated with memory and information processing. The findings suggest caffeine consumption is associated with differential activation in neuronal areas involved in reward, memory, and information processing. Further research on intensity and hedonics of bitter and sweet stimuli in caffeine consumers and non-consumers will be of great interest to better understand the nature of differences in taste perception between caffeine consumers and non-consumers.

Left Posterior Orbitofrontal Cortex Is Associated With Odor-Induced Autobiographical Memory: An fMRI Study

Autobiographical odor memory (AM-odor) accompanied by a sense of realism of a specific memory elicits strong emotions. AM-odor differs from memory triggered by other sensory modalities, possibly because olfaction involves a unique sensory process. Here, we examined the orbitofrontal cortex (OFC), using functional magnetic resonance imaging (fMRI) to determine which OFC subregions are related to AM-odor. Both AM-odor and a control odor successively increased subjective ratings of comfortableness and pleasantness. Importantly, AM-odor also increased arousal levels and the vividness of memories, and was associated with a deep and slow breathing pattern. fMRI analysis indicated robust activation in the left posterior OFC (L-POFC). Connectivity between the POFC and whole brain regions was estimated using psychophysiological interaction analysis (PPI). We detected several trends in connectivity between L-POFC and bilateral precuneus, bilateral rostral dorsal anterior cingulate cortex (rdACC), and left parahippocampus, which will be useful for targeting our hypotheses for future investigations. The slow breathing observed in AM-odor was correlated with rdACC activation. Odor associated with emotionally significant autobiographical memories was accompanied by slow and deep breathing, possibly involving rdACC processing.

Combining Ordinary Kriging with wind directions to identify sources of industrial odors in Portland, Oregon

This study combines Ordinary Kriging, odor monitoring, and wind direction data to demonstrate how these elements can be applied to identify the source of an industrial odor. The specific case study used as an example of how to address this issue was the University Park neighborhood of Portland, Oregon (USA) where residents frequently complain about industrial odors, and suspect the main source to be a nearby Daimler Trucks North America LLC manufacturing plant. We collected 19,665 odor observations plus 105,120 wind measurements, using an automated weather station to measure winds in the area at five-minute intervals, logging continuously from December 2014 through November 2015, while we also measured odors at 19 locations, three times per day, using methods from the American Society of the International Association for Testing and Materials. Our results quantify how winds vary with season and time of day when industrial odors were observed versus when they were not observed, while also mapping spatiotemporal patterns in these odors using Ordinary Kriging. Our analyses show that industrial odors were detected most frequently to the northwest of the Daimler plant, mostly when winds blew from the southeast, suggesting Daimler’s facility is a likely source for much of this odor.

Habituation and adaptation to odors in humans

Habituation, or decreased behavioral response, to odors is created by repeated exposure and several detailed characteristics, whereas adaptation relates to the neural processes that constitute this decrease in a behavioral response. As with all senses, the olfactory system continually encounters an enormous variety of odorants which is why mechanisms must exist to segment them and respond to changes. Although most olfactory habitation studies have focused on animal models, this non-systematic review provides an overview of olfactory habituation and adaptation in humans, and techniques that have been used to measure them. Thus far, psychophysics in combination with modern techniques of neural measurement indicate that habituation to odors, or decrease of intensity, is relatively fast with adaptation occurring more quickly at higher cerebral processes than peripheral adaptation. Similarly, it has been demonstrated that many of the characteristics of habitation apply to human olfaction; yet, evidence for some characteristics such as potentiation of habituation or habituation of dishabituation need more support. Additionally, standard experimental designs should be used to minimize variance across studies, and more research is needed to define peripheral-cerebral feedback loops involved in decreased responsiveness to environmental stimuli.

Nosewitness Identification: Effects of Lineup Size and Retention Interval

Although canine identification of body odor (BO) has been widely used as forensic evidence, the concept of nosewitness identification by human observers was only recently put to the test. The results indicated that BOs associated with male characters in authentic crime videos could later be identified in BO lineup tests well above chance. To further evaluate nosewitness memory, we assessed the effects of lineup size (Experiment 1) and retention interval (Experiment 2), using a forced-choice memory test. The results showed that nosewitness identification works for all lineup sizes (3, 5, and 8 BOs), but that larger lineups compromise identification performance in similarity to observations from eye- and earwitness studies. Also in line with previous eye- and earwitness studies, but in disagreement with some studies on odor memory, Experiment 2 showed significant forgetting between shorter retention intervals (15 min) and longer retention intervals (1-week) using lineups of five BOs. Altogether this study shows that identification of BO in a forensic setting is possible and has limits and characteristics in line with witness identification through other sensory modalities.

Neural Coding of Perceived Odor Intensity

Stimulus intensity is a fundamental perceptual feature in all sensory systems. In olfaction, perceived odor intensity depends on at least two variables: odor concentration; and duration of the odor exposure or adaptation. To examine how neural activity at early stages of the olfactory system represents features relevant to intensity perception, we studied the responses of mitral/tufted cells (MTCs) while manipulating odor concentration and exposure duration. Temporal profiles of MTC responses to odors changed both as a function of concentration and with adaptation. However, despite the complexity of these responses, adaptation and concentration dependencies behaved similarly. These similarities were visualized by principal component analysis of average population responses and were quantified by discriminant analysis in a trial-by-trial manner. The qualitative functional dependencies of neuronal responses paralleled psychophysics results in humans. We suggest that temporal patterns of MTC responses in the olfactory bulb contribute to an internal perceptual variable: odor intensity.

Impact of asthma, exposure period, and filters on human responses during exposures to ozone and its initiated chemistry products

The impact of asthma, exposure period, and filter condition downstream of the mixing box of air-conditioning system on building occupants' perceptual response, work performance, and salivary α-amylase secretion during exposures to ozone and its initiated chemistry products is studied. The experiments were conducted in a field environmental chamber (FEC) (240 m(3)) simulating an office environment. Experiments were conducted during periods when the air-handling system operated with new or used pleated panel filters at constant recirculation (7/h) and ventilation (1/h) rates. Average ozone and secondary organic aerosols (ozone-initiated chemistry products) measured during non-asthmatic and asthmatic subjects' 3-h exposures in the FEC were in the ranges approximately 20-37 ppb and approximately 1.6-3 μg/m(3), respectively. Asthmatic subjects' perceived odor intensity and sensory (eye, nose, and throat) irritation ratings were generally lower than those of non-asthmatic subjects, possibly explaining why asthmatic subjects accept perceived air quality more than non-asthmatic subjects. However, asthmatic subjects' perceived physiological-like symptom ratings (flu, chest tightness, and headache) and concentrations of secreted salivary α-amylase were generally higher than those of non-asthmatic subjects. Asthmatic subjects had significantly lower accuracy than non-asthmatic subjects in a task that required higher concentration although they had higher work speed. Filter condition did not make any significant difference for subjects' responses.

Dietary intakes of fats, fish and nuts and olfactory impairment in older adults

It is unclear whether lifestyle modifications, such as dietary changes, should be advocated to prevent olfactory dysfunction. We investigated the association between dietary intakes of fats (saturated, mono-unsaturated and polyunsaturated fats, and cholesterol) and related food groups (nuts, fish, butter, margarine) with olfactory impairment. There were 1331 and 667 participants (older than 60 years) at baseline and 5-year follow-up, respectively, with complete olfaction and dietary data. Dietary data were collected using a validated semi-quantitative FFQ. Olfaction was measured using the San Diego Odor Identification Test. In a cross-sectional analysis of baseline data, those in the highest v. lowest quartile of n-6 PUFA intake had reduced odds of having any olfactory impairment, multivariable-adjusted OR 0.66 (95% CI 0.44, 0.97), P for trend = 0.06. Participants in the highest v. lowest quartile of margarine consumption had a 65% reduced odds of having moderate/severe olfactory impairment (P for trend = 0.02). Participants in the highest quartile compared to the lowest quartile (reference) of nut consumption had a 46% (P for trend = 0.01) and 58% (P for trend = 0.001) reduced odds of having any or mild olfactory impairment, respectively. Older adults in the highest v. lowest quartile of fish consumption had 35% (P for trend = 0.03) and 50% (P for trend = 0.01) reduced likelihood of having any or mild olfactory impairment, respectively. In longitudinal analyses, a marginally significant association was observed between nut consumption and incidence of any olfactory impairment, highest v. lowest quartile of nut consumption: OR 0.61 (95% CI 0.37, 1.00). Older adults with the highest consumption of nuts and fish had reduced odds of olfactory impairment, independent of potential confounding variables.

Olfactory impairment in older adults is associated with poorer diet quality over 5 years

PURPOSE

Decreased smell could cause appetite suppression and malnutrition. However, there is a paucity of longitudinal data between olfaction and nutritional status in older adults. We aimed to prospectively examine the relationship between olfactory impairment and overall diet quality (reflecting adherence to dietary guidelines) in a population-based cohort of older adults.

METHODS

We used 5-year follow-up data from 557 adults (aged 60+ years at baseline) whose olfaction was measured using the San Diego Odor Identification Test (SDOIT). Dietary data were collected using a validated semiquantitative food frequency questionnaire. A total diet score (TDS) was calculated for intake of selected food groups and nutrients for each participant as described in the national dietary guidelines. Final scores ranged from 0 to 20; higher scores indicated closer adherence to dietary guidelines.

RESULTS

After adjusting for all potential confounders, older adults with moderate/severe olfactory impairment (SDOIT score ≤ 3; lower scores indicate impairment) compared with those with no olfactory impairment had significantly lower adjusted mean (±SE) TDS, 9.09 (0.40) versus 9.94 (0.10), p = 0.04. Women with moderate/severe impaired olfaction (i.e., scored poorly on the odor identification test) compared with those with normal olfaction had significantly lower adjusted mean TDS, 8.87 (0.69) versus 10.31 (0.13), p = 0.04. No associations were observed between olfaction and TDS in men.

CONCLUSIONS

Olfactory impairment in older women could signal an increased risk of poorer diet quality, defined as adherence to national dietary guidelines. Additional longitudinal studies are needed to confirm or refute the observed link between olfactory loss and overall patterns of food intake in older adults.

Time-course of trigeminal versus olfactory stimulation: evidence from chemosensory evoked potentials

Habituation of responses to chemosensory signals has been explored in many ways. Strong habituation and adaptation processes can be observed at the various levels of processing. For example, with repeated exposure, amplitudes of chemosensory event-related potentials (ERP) decrease over time. However, long-term habituation has not been investigated so far and investigations of differences in habituation between trigeminal and olfactory ERPs are very rare. The present study investigated habituation over a period of approximately 80 min for two olfactory and one trigeminal stimulus, respectively. Habituation was examined analyzing the N1 and P2 amplitudes and latencies of chemosensory ERPs and intensity ratings. It was shown that amplitudes of both components - and intensity ratings - decreased from the first to the last block. Concerning ERP latencies no effects of habituation were seen. Amplitudes of trigeminal ERPs diminished faster than amplitudes of olfactory ERPs, indicating that the habituation of trigeminal ERPs is stronger than habituation of olfactory ERPs. Amplitudes of trigeminal ERPs were generally higher than amplitudes of olfactory ERPs, as it has been shown in various studies before. The results reflect relatively selective central changes in response to chemosensory stimuli over time.

Education level predicts retrospective metamemory accuracy in healthy aging and Alzheimer's disease

The current study investigated the effect of education on retrospective metamemory accuracy in 143 healthy older adults and 143 early to moderate Alzheimer's disease (AD) patients, using retrospective measures of confidence in the accuracy of retrieval responses in an episodic odor recognition memory task. Relative confidence accuracy was computed as the difference between confidence judgments for correct and incorrect responses. In both AD patients and controls, individuals reporting 17 years of education or more had significantly more accurate levels of confidence than individuals with 12 years or less. Thus, education was a significant predictor of retrospective metamemory accuracy in healthy aging and AD.

Analgesia Is Enhanced by Providing Information regarding Good Outcomes Associated with an Odor: Placebo Effects in Aromatherapy?

No previous report has described whether information regarding an odor used in aromatherapy has placebo effects. We investigated whether placebo analgesia was engendered by verbal information regarding the analgesic effects of an odor. Twelve of 24 subjects were provided with the information that a lavender odor would reduce pain (informed), whereas the other 12 subjects were not (not-informed). Concurrent with respiration recording, the subjects were administered a lavender-odor or no-odor treatment during application of painful stimulation to the forefinger. The subjects reported their experience of pain and its unpleasantness on a visual analogue scale after the painful stimulation. The lavender-odor treatment significantly alleviated pain and unpleasantness compared with the no-odor treatment in the informed (P < 0.01) and not-informed groups (P < 0.05). The no-odor treatment in the informed group significantly alleviated pain and unpleasantness compared with both the no-odor and lavender-odor treatments in the not-informed group (P < 0.05). Rapid and shallow breathing induced by the painful stimulation became slow and deep during the lavender-odor and no-odor treatments in both groups. Information regarding a lavender odor, the lavender odor itself, and slower breathing contributed to reduced perceptions of pain and unpleasantness during painful stimulation, suggesting that placebo effects significantly contribute to analgesia in aromatherapy.

The perception of odor is not a surrogate marker for chemical exposure: a review of factors influencing human odor perception

CONTEXT

Clinical toxicologists perform risk assessments and clinical evaluations for patients with potential exposure to airborne toxicants in which the patient's self-reported perception of odor may be the only indicator that an exposure may have taken place.

OBJECTIVE

To review the factors that may affect the human ability to perceive chemical odors and relate those odors to specific chemical exposures.

METHODS

The medical literature, from 1950 through 2012, was searched using the OVID database and the PUBMED database. The searches returned 238 articles, of which 113 involved human studies and were published in the English language. Of these 113 articles, 40 articles discussed odor issues and thus were chosen as specifically relevant to the topic. Bibliographies of all articles were also searched for other relevant references and this found six additional articles, making a total of 46. FACTORS THAT MAY AFFECT OLFACTION AND THE ABILITY TO PERCEIVE ODOR: Genetic/population: Ethnic background is associated with widely differing odor detection abilities and thresholds. A significant genetic influence for the ability to smell and perceive odor has been reported. Gender: Women are superior to men in their ability to identify odors. Age. Increasing age is correlated with higher odor detection thresholds. Medical conditions: A variety of medical conditions have been associated with deficits in olfaction, including diseases of the nose and sinuses, multiple sclerosis, and schizophrenia. Alcoholism and smoking: Abuse of alcohol results in impaired olfactory sense, and smoking tobacco products alters odor detection threshold in a dose-related manner. Occupational and environmental factors: Repeated inhalation of any chemical results in olfactory fatigue over relatively short time frames that leads to a decreased ability to accurately detect and identify an odor. Recent exposure to relatively high concentrations of a chemical has been shown to affect sensitivity to that particular odorant, altering subsequent detection thresholds by up to three orders of magnitude. Applicability of proposed odor thresholds: Humans are only able to identify three to four components of complex olfactory mixtures and the odorants present in the mixture affect which individual components are detected. Odorants present in suprathreshold concentrations in a mixture may effectively mask the presence of odorants present in perithreshold concentrations. Self-rating of olfactory function may not correlate with actual olfactory ability. It is even more difficult to accurately determine intensity of an odor in a quantifiable way. For example, under conditions of constant stimulation with hydrogen sulfide, perceptual intensity was reported to decrease exponentially with time of stimulation. Concomitant visual stimulation also affects odor intensity. Some chemicals, such as hydrogen sulfide, may induce reactions in humans related solely to their odor, even when they are present in concentrations substantially lower than those levels usually associated with the development of adverse clinical effects. There is a wealth of literature suggesting that the intensity of perceived odor, the degree of irritation, and the reported health effects of exposure to an odorant chemical are affected by psychological state and bias. Multiple theories have been proposed to explain the cognitive basis for perceived illness in association with the perception of odor. The concept of odor has been reported to be intrinsically and cognitively associated with illness rather than with health. Assigning negative bias to an odor prior to an exposure results in the reporting of significantly more health-related symptoms following exposure. This suggests that those symptoms are not mediated by the odor directly, but rather by an individual's cognitive associations between odor and health.

CONCLUSIONS

Attempts to verify exposure intensity based on the report of a perceived odor is unreliable and has no useful application in legitimate exposure assessment paradigms. Detection of an odor does not imply a medically significant exposure to a toxicant and, due to subject bias and the difficulty of detecting individual odorants in mixtures, may not constitute an exposure to the purported substance.

Individuals at risk for Alzheimer's disease show differential patterns of ERP brain activation during odor identification

BACKGROUND

Studies suggest that older adults at risk of developing Alzheimer's disease may show olfactory processing deficits before other signs of dementia appear.

METHODS

We studied 60 healthy non-demented individuals, half of whom were positive for the genetic risk factor the Apolipoprotein E ε4 allele, in three different age groups. Event-related potentials to visual and olfactory identification tasks were recorded and analyzed for latency and amplitude differences, and plotted via topographical maps.

RESULTS

Varying patterns of brain activation were observed over the post-stimulus epoch for ε4- versus ε4+ individuals on topographical maps. Individuals with the ε4 allele demonstrated different ERP peak latencies during identification of olfactory but not visual stimuli. High correct ApoE classification rates were obtained utilizing the olfactory ERP.

CONCLUSIONS

Olfactory ERPs demonstrate functional decline in individuals at risk for Alzheimer's disease at much earlier ages than previously observed, suggesting the potential for pre-clinical detection of AD at very early stages.

Prevalence and neurodegenerative or other associations with olfactory impairment in an older community

OBJECTIVE

To determine the prevalence of olfactory impairment and its associations with neurodegenerative and other conditions in older adults.

METHOD

1,636 participants (>/=60 years) enrolled in the Blue Mountains Eye Study (2002-2004) were analyzed. Olfaction was assessed by the San Diego Odor Identification Test and used to classify mild impairment (4 or 5), moderate impairment (</=3), or any impairment (<6).

RESULTS

Prevalent olfactory impairment was 27.0%. After multivariate adjustment, the likelihood increased twofold with each decade of life after 60 years and was higher in men than women. Olfactory impairment and body mass index (BMI) were inversely associated. Persons with Parkinson's disease and cognitive impairment had an increased likelihood of mild and moderate olfactory impairment.

DISCUSSION

Over one in four older persons had olfactory impairment. The prevalence was higher in men, increased with age and decreasing BMI, and was higher among persons with Parkinson's disease and cognitive impairment.

Olfactory ERPs in an odor/visual congruency task differentiate ApoE ε4 carriers from non-carriers

Alzheimer's disease (AD) is a progressive, neurodegenerative disorder that impairs memory and semantic processing. AD patients and MCI patients at risk for AD show altered N400 ERP responses to incongruent visual and verbal stimuli. AD patients exhibit neuropathology in olfactory brain areas before cognitive symptoms, suggesting the potential for olfactory processing to reflect early pathology. Despite this, odor congruency has not been examined. We investigated odor-image congruency in older adults at genetic risk for AD. ApoE ε4 carriers and non-carriers were screened for anosmia, severe hyposmia, and dementia. Olfactory ERPs were measured 600-1300 ms following odor-image pairs. Odors were each presented once congruently and once incongruently via an olfactometer. Pz amplitude significantly decreased on incongruent trials in e4 carriers. Pz amplitude differences on congruous and incongruous trials were larger in non carriers. Regression indicated that congruency showed very high sensitivity and specificity for correctly classifying ε4 carriers from non-carriers.

The association between olfactory impairment and total mortality in older adults

BACKGROUND

Population-based data on the relationship between impaired olfaction and risk of mortality among older adults are lacking. We used a representative cohort of adults aged 60 years or older to assess whether olfactory loss is a predictor of mortality, independent of potential confounders.

METHODS

Olfaction was measured by the San Diego Odor Identification Test (SDOIT) among 1,636 participants enrolled in the Blue Mountains Eye Study (2002-2004). Five-year all-cause mortality was confirmed using the Australian National Death Index.

RESULTS

More than one in five participants (21.8%) with olfactory impairment had died over the 5 years compared with less than 10% of participants without olfactory loss. Moderate olfactory loss (SDOIT score ≤3) was associated with a 68% increased risk of all-cause mortality (multivariable-adjusted hazard ratio, 1.68; 95% confidence interval, 1.10-2.56). This association did not persist after further adjustment for cognitive impairment. The association between olfactory loss and all-cause mortality was more marked among older participants (≥70 years) than younger participants (<70 years) with olfactory impairment (multivariable-adjusted hazard ratio, 1.48; 95% confidence interval, 1.02-2.15). However, adjusting for cognitive impairment diminished this association.

CONCLUSIONS

Older adults with moderately impaired olfaction compared with those with normal olfaction had a higher risk of dying 5 years later. The relationship between olfaction and mortality, however, may be largely mediated by cognitive impairment in these older adults. Our findings highlight the value of identifying olfactory loss in the preclinical stage in the older patient before the development of related comorbidities.

Calcium-stores mediate adaptation in axon terminals of olfactory receptor neurons in Drosophila

Background

In vertebrates and invertebrates, sensory neurons adapt to variable ambient conditions, such as the duration or repetition of a stimulus, a physiological mechanism considered as a simple form of non-associative learning and neuronal plasticity. Although various signaling pathways, as cAMP, cGMP, and the inositol 1,4,5-triphosphate receptor (InsP₃R) play a role in adaptation, their precise mechanisms of action at the cellular level remain incompletely understood. Recently, in Drosophila, we reported that odor-induced Ca²⁺-response in axon terminals of olfactory receptor neurons (ORNs) is related to odor duration. In particular, a relatively long odor stimulus (such as 5 s) triggers the induction of a second component involving intracellular Ca²⁺-stores.

Results

We used a recently developed in-vivo bioluminescence imaging approach to quantify the odor-induced Ca²⁺-activity in the axon terminals of ORNs. Using either a genetic approach to target specific RNAs, or a pharmacological approach, we show that the second component, relying on the intracellular Ca²⁺-stores, is responsible for the adaptation to repetitive stimuli. In the antennal lobes (a region analogous to the vertebrate olfactory bulb) ORNs make synaptic contacts with second-order neurons, the projection neurons (PNs). These synapses are modulated by GABA, through either GABAergic local interneurons (LNs) and/or some GABAergic PNs. Application of GABAergic receptor antagonists, both GABA_A or GABA_B, abolishes the adaptation, while RNAi targeting the GABAB_R (a metabotropic receptor) within the ORNs, blocks the Ca²⁺-store dependent component, and consequently disrupts the adaptation. These results indicate that GABA exerts a feedback control. Finally, at the behavioral level, using an olfactory test, genetically impairing the GABA_BR or its signaling pathway specifically in the ORNs disrupts olfactory adapted behavior.

Conclusion

Taken together, our results indicate that a relatively long lasting form of adaptation occurs within the axon terminals of the ORNs in the antennal lobes, which depends on intracellular Ca²⁺-stores, attributable to a positive feedback through the GABAergic synapses.

Olfactory impairment in older adults is associated with depressive symptoms and poorer quality of life scores

OBJECTIVES

We assessed the association between impaired olfaction and depressive symptoms and poor quality of life.

METHODS

A total of 1,375 participants aged 60 years or older had their olfaction measured using the San Diego Odor Identification Test. Quality of life was assessed using the 36-Item Short-Form Survey (SF-36). Depressive symptoms were assessed by either the SF-36, which included the Mental Health Index, and/or the Center for Epidemiologic Studies Depression Scale (CES-D-10).

RESULTS

Among participants with olfactory impairment, 15.4% and 20.2% had depressive symptoms assessed by the Mental Health Index and CES-D-10, respectively. Among participants aged 70 years or older, olfactory impairment was associated with depressive symptoms (assessed by the CES-D-10), multivariate-adjusted odds ratio, OR: 1.66 (95% confidence interval, CI: 1.03-2.66). Subjects with olfactory impairment compared to those without, had lower SF-36 scores in six out of the eight indices.

CONCLUSIONS

Olfactory impairment was independently associated with depressive symptoms and poorer quality of life.

Presynaptic Ca2+ stores contribute to odor-induced responses in Drosophila olfactory receptor neurons

In both vertebrates and invertebrates, olfactory receptor neurons (ORNs) respond to several odors. They also adapt to stimulus variations, and this is considered to be a simple form of non-associative learning and neuronal plasticity. Different mechanisms have been described to support neuronal and/or synaptic plasticity. For example in vertebrates, presynaptic Ca(2+) stores relying on either the ryanodine receptor (RyR) or the inositol (1,4,5)-trisphosphate receptor (InsP(3)R) have been reported to participate in synaptic transmission, in hippocampal pyramidal neurons, and in basket cell-Purkinje cell synapses. However, in invertebrates, especially in sensory neurons such as ORNs, similar mechanisms have not yet been detected. In this study, using Drosophila and taking advantage of an in vivo bioluminescence Ca(2+)-imaging technique in combination with genetic and pharmacological tools, first we show that the GFP-aequorin Ca(2+) sensor is sensitive enough to detect odor-induced responses of various durations. Second, we show that for a relatively long (5 s) odor application, odor-induced Ca(2+) responses occurring in the axon terminals of ORNs involve intracellular Ca(2+) stores. This response is decreased by specifically targeting InsP(3)R or RyR by RNAi, or application of the specific blockers thapsigargin or ryanodine, suggesting that Ca(2+) stores serve to amplify the presynaptic signal. Furthermore, we show that disrupting the intracellular Ca(2+) stores in the ORNs has functional consequences since InsP(3)R- or RyR-RNAi expressing flies were defective in olfactory behavior. Altogether, our results indicate that for long odor applications in Drosophila, the olfactory response depends on intracellular Ca(2+) stores within the axon terminals of the ORNs.

Intensity of odor and sensory irritation as a function of hexanal concentration and interpresentation intervals: an exploratory study

Hexanal is a suspected irritant in indoor air. Free-number magnitude estimation was used to measure intensity of odor and sensory irritation of two test concentrations (64 or 178 ppb) as a function of five concentrations and four interpresentation intervals. 9 of 12 participants (6 men, 6 women, ages 20-30 years) were able to detect the odor and report sensory irritation. The method of constant stimuli was applied to calculate the absolute thresholds of hexanal, which were 25 ppb for odor and 281 ppb for sensory irritation. Well-fitting power functions had a higher exponent for sensory-irritation intensity than for odor intensity (0.71 vs 0.66). A statistically significant effect on odor intensity was found for the concentration of presentations preceding the test stimuli and an interaction between concentrations and interpresentation intervals; however, sensory irritation was experienced to last longer than the odor of the same concentration.

Familial aggregation of olfactory impairment and odor identification in older adults

OBJECTIVES/HYPOTHESIS

The objective of this analysis was to estimate the genetic contributions to olfactory impairment.

STUDY DESIGN

Population based.

METHODS

Olfactory impairment was measured using the San Diego Odor Identification Test at the 5-year follow-up examination for the population-based Epidemiology of Hearing Loss study. Subjects were classified as impaired if they correctly identified fewer than six out of eight odorants. To reduce confounding by age, analysis was restricted to subjects who were 60 to 79 years of age. Familial aggregation was evaluated by heritability estimates, tetrachoric correlations, and odds ratios in 207 sibling pairs from 135 sibships.

RESULTS

The prevalence of olfactory impairment was 20.2% overall and was higher in men. After adjustment for sex, age, and smoking, heritability of olfactory impairment was moderate (h(2) = 0.55), although not statistically significantly different from 0 (P = .09). By contrast, the adjusted heritability estimate for bubble gum, one of the individual odorants, was significant (h(2) = 0.51; P = .01).

CONCLUSIONS

Genetic factors might contribute to general olfactory impairment in older adults, but the strength of familial aggregation differs for individual odorants, a finding consistent with prior research.

Multiple sensory impairment and quality of life

PURPOSE

To evaluate the independent impact of vision, hearing, and olfactory impairment on quality of life.

METHODS

Subjects (n = 1854, mean age = 67 years) were participants in the 1998-2000 and 2003-05 examinations of the Epidemiology of Hearing Loss Study and Beaver Dam Eye Study, population-based, prospective studies set in Beaver Dam, Wisconsin. Sensory capacities were measured in 1998-2000 and quality of life was measured in 2003-05. Vision impairment was assessed using current binocular visual acuity and contrast sensitivity. Hearing impairment was defined by the pure tone threshold average and word recognition scores in competing message and olfaction was measured with the San Diego Odor Identification Test. The Short Form 36 Health Survey (SF-36) was used to assess quality of life.

RESULTS

Significant independent effects of vision impairment and hearing impairment on the SF-36 social functioning domain score were observed (P < 0.01). The adjusted mean social functioning score for participants with vision and hearing impairment was 5.9 units lower than the mean score in participants with no vision and hearing impairment. A significant independent effect of vision impairment was also observed for the physical functioning and mental health domains (P < 0.01). Olfaction impairment was not significantly associated with the SF-36 indices.

CONCLUSIONS

Impairments in vision and hearing demonstrated independent effects on quality of life. The impact was observed for physical and emotional health (vision) and social functioning (vision and hearing). Evaluation and rehabilitation of sensory deficits may contribute to an improvement in functioning and well-being in the later years of life.

Developmental differences in memory for cross-modal associations

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

Age-related differences in the neural substrates of cross-modal olfactory recognition memory: an fMRI investigation

Impaired ability to remember what has gone before is one of the most distressing aspects of the aging process. Odor recognition memory is particularly vulnerable to the effects of aging, yet the underlying neural substrate is unknown. This study investigated the neural substrate of cross-modal olfactory recognition memory in young and older adults using fMRI. Participants were presented with 16 familiar odors immediately before entering the scanner, and were then tested for retrieval with words, either names of odors previously presented (targets) or names of new odors (foils), while being scanned at 3 T. Activation was reduced in the old subjects, both in regions involved in episodic memory retrieval and in regions involved in olfactory processing. Greater activation in the cerebellum of older adults was observed, suggesting increased response to attentional demands or compensatory mechanisms. Unlike in a number of studies in other sensory modalities, no increase in activation in frontal areas in older adults was observed during retrieval.

Differential effects of normal aging on memory for odor-place and object-place associations

Odor-place and object-place associative memory were compared in healthy older (over the age of 65) and young (18 to 25 years of age) adults. Twelve spatial locations were defined on a tabletop board. Either six odors or six objects were presented one at a time and each was paired with a location on the board. The participant then was presented with each stimulus individually and asked to place it in its paired location. Older adults showed impaired odor-place associative memory but unimpaired object-place memory compared to young adults. Item recognition memory for the individual stimuli or locations used on the associative memory task was similar in both groups. The results suggest that odor-place associative memory is particularly affected by age-related brain changes.

Sexual differentiation in sensitivity to male body odor(1)

We have confirmed that more female subjects than male subjects evaluate male body odor as significantly unpleasant. Through an investigation on sexual differentiation in sensitivity to male body odor, we concluded that one of the volatile steroids, androstenone, had two effects on female olfactory sense. First, female subjects perceived androstenone itself to be more unpleasant than male subjects. Second, for only female subjects, androstenone, at a concentration of one-tenth of detection threshold, enhanced the intensity and unpleasantness of body-odor constituents such as short-chain fatty acids.

Apolipoprotein E epsilon4 genotype and gender: effects on memory

OBJECTIVE

Episodic recognition memory for odors and visual was assessed in apolipoprotein E (ApoE) epsilon4-positive and epsilon4-negative men and women diagnosed with Alzheimer disease (AD) and a healthy age- and gender-matched comparison group.

METHODS

A total of 38 AD patients and 38 age- and gender-matched healthy older adults completed a recognition memory task involving three categories of stimuli: odors, faces, and symbols.

RESULTS

In the healthy comparison group, men who were epsilon4 negative outperformed epsilon4-positive men in recognition memory for odors and committed fewer false-positive errors. However, there were no significant differences between epsilon4-negative and epsilon4-positive women in the comparison group. No significant gender or ApoE status differences were detected in recognition memory for faces or symbols in the comparison group. In patients with AD, epsilon4-negative women outperformed epsilon4-positive women in recognition memory for odors and committed significantly fewer false-positive errors. However, there were no significant differences between epsilon4-positive and epsilon4-negative men. There were no significant gender or ApoE status differences in recognition memory for faces or symbols in AD patients.

CONCLUSION

The results demonstrate that recognition memory for olfactory stimuli may be particularly impaired in healthy older men with the epsilon4 allele. In patients with AD, odor memory impairments may be less severe in women who are negative for the epsilon4 allele. The results offer new insight into how recognition memory is affected by gender, the epsilon4 allele, and the modality of the stimulus to be remembered in healthy older adults and patients with AD.