Olfactory Detection Thresholds Research Articles

The Training Level of Experts Influences their Detection Thresholds for Key Wine Compounds

Wine experts usually rely on chemical tracers of qualities or defects to judge wines. While part of their expertise is determined by their sensory ability to detect these key compounds, their level of sensitivity is generally unknown. The olfactory detection thresholds for 10 key odorant compounds in wine were, therefore, measured in a large sample of professionals (100 3 log10 units). Comparing the abilities of the experts to detect the whole sample of chemicals tested, we showed that their sensitivity profiles were very different. Detection threshold distribution asymmetries suggested specific hyposmias or hyperosmias for b-ionone, 2-isobutyl-3-methoxypyrazine, 2,4,6-trichloroanisole, diacetyl, and linalool. Interestingly, we found that academic degrees in tasting and enology do have an impact on odor detection thresholds for two compounds, diacetyl and mixed ethylphenols.

Olfactory Detection Thresholds and Adaptation in Adults with Autism Spectrum Condition

Sensory issues have been widely reported in Autism Spectrum Conditions (ASC). Since olfaction is one of the least investigated senses in ASC, the current studies explore olfactory detection thresholds and adaptation to olfactory stimuli in adults with ASC. 80 participants took part, 38 (18 females, 20 males) with ASC and 42 control participants (20 males, 22 females). A subgroup of participants (N = 19 in each group) also conducted an adaptation task. Standardized "Sniffin' Sticks" were used to measure olfactory detection levels and adaptation. Adults with and without ASC showed similar olfactory detection thresholds, and similar adaptation to an olfactory stimulus. Since diminished adaptation in ASC has been previously suggested, future research needs to examine adaptation in other modalities as well.

Agreeable Smellers and Sensitive Neurotics – Correlations among Personality Traits and Sensory Thresholds

Correlations between personality traits and a wide range of sensory thresholds were examined. Participants (N = 124) completed a personality inventory (NEO-FFI) and underwent assessment of olfactory, trigeminal, tactile and gustatory detection thresholds, as well as examination of trigeminal and tactile pain thresholds. Significantly enhanced odor sensitivity in socially agreeable people, significantly enhanced trigeminal sensitivity in neurotic subjects, and a tendency for enhanced pain tolerance in highly conscientious participants was revealed. It is postulated that varied sensory processing may influence an individual's perception of the environment; particularly their perception of socially relevant or potentially dangerous stimuli and thus, varied with personality.

Ghrelin Enhances Olfactory Sensitivity and Exploratory Sniffing in Rodents and Humans

Olfaction is an integral part of feeding providing predictive cues that anticipate ingestion. Although olfactory function is modulated by factors such as prolonged fasting, the underlying neural mechanisms remain poorly understood. We recently identified ghrelin receptors in olfactory circuits in the brain. We therefore investigated the role of the appetite-stimulating hormone ghrelin in olfactory processing in rodents and humans, testing the hypothesis that ghrelin lowers olfactory detection thresholds and enhances exploratory sniffing, both being related to food seeking. In rats, intracerebroventricular ghrelin decreased odor detection thresholds and increased sniffing frequency. In humans, systemic ghrelin infusions significantly enhanced sniff magnitudes in response to both food and nonfood odorants and air in comparison to control saline infusions but did not affect the pleasantness ratings of odors. This is consistent with a specific effect on odor detection and not the hedonic value of odors. Collectively, our findings indicate that ghrelin stimulates exploratory sniffing and increases olfactory sensitivity, presumably enhancing the ability to locate, identify, and select foods. This novel role is consistent with ghrelin's overall function as a signal amplifier at the molecular interface between environmental and nutritional cues and neuroendocrine circuits controlling energy homeostasis.

Change of olfactory function associated structures in Parkinson's disease: a voxel ⁃ based morphometry study

Objective To investigate the structural differences of olfactory associated brain areas between patients with Parkinson's disease (PD) and normal controls, and their relationship to olfactory dysfunction by voxel ⁃ based morphometry (VBM), and to explore the possibility for early diagnosis. Methods Olfactory detection threshold (DT) and olfactory identification threshold (IT) were determined with five odors olfactory detection arrays kit provided by Chinese Academy of Sciences on 26 PD patients, and 26 age and gender matched healthy controls. The relationship between olfactory function and age or duration or severity degree [total Unified Parkinson's Disease Rating Scale (UPDRS) scores] was analysed. The analysis of brain structures were performed at a Siemens 3.0T by using magnetization prepared rapid gradient echo imaging (MPRAGE). The data were processed by using SPM5. Results The olfactory thresholds (DT and IT) of PD patients (0.66 ± 0.84, 2.41 ± 0.74) were significantly higher than those of the controls (⁃ 0.64 ± 0.83, 1.08 ± 0.54; Z = 4.455, P = 0.000; t = 4.898, P = 0.000). No significant correlations were seen between olfactory thresholds (DT and IT) and age (DT: rs = 0.199, P = 0.330; IT: rs = 0.256, P = 0.207) or duration (DT: rs = 0.123, P = 0.550; IT: rs = 0.055, P = 0.789) or UPDRS Ⅲ scores (DT: rs = 0.229, P = 0.260; IT: rs = 0.379, P = 0.056) in all PD patients. Compared to controls, significant clusters of increased white matter density were found in bilateral occipital lobes (BA17-19), left posterior cingulate gyrus (BA23, 30, 31) and left paracentral lobule (BA3-5) in PD patients. Significant clusters of increased white matter volume included bilateral occipital lobes (BA17-19), left posterior cingulate gyrus (BA23, 30, 31) and left paracentral lobule (BA3-5). Meanwhile, there were negative relationship between the increase of white matter density in left posterior cingulate gyrus and olfactory IT (rs = 0.496, P = 0.010). Conclusion The olfactory function was found significantly decreased in PD patients, and unrelated to age and duration. Changes of olfactory associated structures, particularly the white matter areas were found by using VBM in early PD with olfactory dysfunction. Our data suggest that early olfactory dysfunction in PD results from changes in the brain areas associated with processing olfaction. VBM can be widely used for the analysis of the diagnosis of PD or neurodegenerative diseases. DOI：10.3969/j.issn.1672-6731.2011.01.012

Olfactory sensitivity for sperm-attractant aromatic aldehydes: a comparative study in human subjects and spider monkeys

Using a three-alternative forced-choice ascending staircase procedure, we determined olfactory detection thresholds in 20 human subjects for seven aromatic aldehydes and compared them to those of four spider monkeys tested in parallel using an operant conditioning paradigm. With all seven odorants, both species detected concentrations <1 ppm, and with several odorants single individuals of both species even discriminated concentrations <1 ppb from the solvent. No generalizable species differences in olfactory sensitivity were found despite marked differences in neuroanatomical and genetic features. The across-odorant patterns of sensitivity correlated significantly between humans and spider monkeys, and both species were more sensitive to bourgeonal than to lilial, cyclamal, canthoxal, helional, lyral, and 3-phenylpropanal. No significant correlation between presence/absence of an oxygen-containing moiety attached to the benzene ring or presence/absence of an additional alkyl group next to the functional aldehyde group, and olfactory sensitivity was found in any of the species. However, the presence of a tertiary butyl group in para position (relative to the functional aldehyde group) combined with a lack of an additional alkyl group next to the functional aldehyde group may be responsible for the finding that both species were most sensitive to bourgeonal.

Comparison of two different odorants in an olfactory detection threshold test of the Sniffin’ Sticks

The olfactory test battery Sniffin’ Sticks is a test of nasal chemosensory function that is based on pen-like devices for odour presentation. It consists of three olfactory subtests: threshold, discrimination, and identification. The detection threshold can be measured using two different odorants--n-butanol or PEA (phenylethyl alcohol). Both tasks are commonly applied in published studies, but little is known about the formal comparison of values obtained using them. Unlike the Sniffin’ Sticks with n-butanol as odorant, there is poor validation for the threshold subtest with the odorant PEA. The purpose of this study was to compare these two different odorants. Both odorants were applied to 100 normosmic, healthy subjects (50 females). The experiment was divided into two sessions performed on two different days. After each threshold test the discrimination and identification subtests were conducted. We obtained significant differences in detection thresholds of PEA and n-butanol. The mean score of PEA threshold and PEA TDI (sum of threshold, discrimination, identification) was significantly higher compared to n-butanol. No significant correlation between individual PEA and n-butanol thresholds was observed. The differences between both odorants indicate that a formal validation of the Sniffin’ Sticks with PEA as odorant for probing olfactory thresholds may be required.

Comparison of two different odorants in an olfactory detection threshold test of the Sniffin’ Sticks

The olfactory test battery Sniffin’ Sticks is a test of nasal chemosensory function that is based on pen-like devices for odour presentation. It consists of three olfactory subtests: threshold, discrimination, and identification. The detection threshold can be measured using two different odorants--n-butanol or PEA (phenylethyl alcohol). Both tasks are commonly applied in published studies, but little is known about the formal comparison of values obtained using them. Unlike the Sniffin’ Sticks with n-butanol as odorant, there is poor validation for the threshold subtest with the odorant PEA. The purpose of this study was to compare these two different odorants. Both odorants were applied to 100 normosmic, healthy subjects (50 females). The experiment was divided into two sessions performed on two different days. After each threshold test the discrimination and identification subtests were conducted. We obtained significant differences in detection thresholds of PEA and n-butanol. The mean score of PEA threshold and PEA TDI (sum of threshold, discrimination, identification) was significantly higher compared to n-butanol. No significant correlation between individual PEA and n-butanol thresholds was observed. The differences between both odorants indicate that a formal validation of the Sniffin’ Sticks with PEA as odorant for probing olfactory thresholds may be required.

Human Male Superiority in Olfactory Sensitivity to the Sperm Attractant Odorant Bourgeonal

Recent studies have shown that sperm chemotaxis critically involves the human olfactory receptor OR1D2, which is activated by the aromatic aldehyde bourgeonal. Given that both natural and sexual selection may act upon the expression of receptors, we hypothesized that human males are more sensitive than human females for bourgeonal. Using a 3-alternative forced-choice test procedure, olfactory detection thresholds were determined for a total of 500 subjects, 250 males, and 250 females between 18 and 40 years of age. We found that male subjects detected bourgeonal at significantly lower concentrations (mean value: 13 ppb) compared with female subjects (mean value: 26 ppb), whereas no such gender difference in olfactory sensitivity was found with helional, a structural analog of bourgeonal, and with n-pentyl acetate, an aliphatic ester, which were tested in parallel. Males and females did not differ in their frequency of specific anosmia for any of the 3 odorants. The frequency distributions of olfactory detection thresholds were monomodal with all 3 odorants in both genders. Olfactory detection thresholds did not differ significantly between pre- and postovulatory females with any of the 3 odorants. To the best of our knowledge, this is the first study ever to find a human male superiority in olfactory sensitivity. Single nucleotide polymorphisms and/or copy number variations in genes coding for olfactory receptors may be the proximate cause for our finding, whereas a gender difference in the behavioral relevance of bourgeonal may be the ultimate cause.

Olfactory Perception of 6 Amino Acids by Human Subjects

The olfactory properties of 6 amino acids were assessed in 20 human subjects using psychophysical tests of detectability, discriminability, and chemesthesis. Mean olfactory detection thresholds were found to be 10 microM for D-methionine, 80 microM for L-methionine, 200 microM for L-cysteine, 220 microM for D-cysteine, 75 mM for D-proline, and 100 mM for L-proline. When presented at clearly detectable and intensity-matched concentrations, the subjects readily discriminated between the odors of the L-forms of cysteine, methionine, and proline, whereas they failed to distinguish between the L- and D-forms of a given amino acid. The subjects also failed in localizing the side of monorhinal stimulation with all 6 amino acids when presented at the same concentrations as in the discrimination tasks. These results suggest that amino acids may contribute to the flavor of food not only as taste stimuli but also as olfactory stimuli perceived via ortho- or retronasal smelling. In contrast, it is unlikely that amino acids contribute to flavor perception via chemesthesis. Given that the odors of 4 of the 6 amino acids tested here were detected at concentrations lower than their corresponding taste detection thresholds, this may have important implications for the widespread use of amino acids as food additives as well as for the evaluation of off-flavors caused by amino acids.

How big is the gap between olfactory detection and recognition of aliphatic aldehydes?

The aim of the present study was to determine the magnitude of the difference in concentration between olfactory detection and recognition thresholds of aliphatic aldehydes. To this end, we first determined olfactory detection thresholds for n-butanal, n-pentanal, n-hexanal, n-heptanal, and n-octanal in a group of 16 subjects and then assessed their ability to discriminate between all possible binary pairs of the same odorants presented at different concentrations above their individual detection thresholds. We found that the gap between detection and recognition of aliphatic aldehydes is odorant pair dependent and, at the group level, spans at least a factor of 100. However, single subjects successfully discriminated between certain aldehyde pairs presented at a factor as low as 3 above detection threshold. Our approach to determining olfactory recognition thresholds, using a performance-based measure rather than verbal labeling, not only avoids the problem of semantic ambiguity and arguable criteria, but also is applicable to nonhuman species, allowing for interspecific comparisons of recognition thresholds and of the gap between detection and recognition of odorants. The raw discrimination data from this study are available as a supplement from http://app.psychonomic-journals.org/content/supplemental.

Attitudes toward Everyday Odors for Children with Visual Impairments: A Pilot Study

The question of how the processing of stimuli from the external world is organized or reorganized when a sensory modality is altered or missing has been the subject of numerous studies, although the studies have mostly been on tactile and auditory abilities (Hatwell, 2003). In contrast, olfaction has been poorly investigated in people who are visually impaired, despite the increasing evidence that humans have a keen sense of smell (Schaal & Porter, 1991). Odors influence mood; well-being (Ehrlichman & Bastone, 1992); and social interactions, such as the choice of partners (Herz & Inzlicht, 2002). Emotional and social implications of odors go back to the earliest periods of development (Schaal, 1988). Olfaction should thus be considered a significant source of environmental information and emotions in persons with visual impairments. Most, if not all, studies of the relationship between olfaction and blindness aimed to test the intuitive hypothesis of increased sensitivity of the unimpaired senses (for a review, see Ferdenzi, Holley, & Schaal, 2004). The comparison of olfactory detection thresholds in participants with and without visual impairments first led to inconsistent results (Boccuzzi, 1962; Griesbach, 1899). More recent studies that have used more reliable methods found no difference between the two groups in olfactory sensitivity, discrimination, or cued identification (that is, the choice of the name of an odor from among several alternatives) (Diekmann, Walger, & von-Wedel, 1994; Schwenn, Hundorf, Moll, Pitz, & Mann, 2002; Smith, Doty, Burlingame, & McKeown, 1993). Conversely, more ecological perceptual tasks, such as noncued odor identification, revealed better performances by participants with visual impairments (Murphy & Cain, 1986; Rosenbluth, Grossman, & Kaitz, 2000; Wakefield, Homewood, & Taylor, 2004). This advantage was interpreted as reflecting higher attention to olfactory stimuli, resulting in deeper knowledge and the better ability to reactivate associated information. Thus, possible differences in favor of people with visual impairments may be a result more of advantages in attentional strategies than of enhanced sensitivity. This view was advocated by Tilney (1929), who examined Helen Keller: [Her] olfactory sense shows nothing above the normal average.... Her sensory supremacy is entirely in the realm of intellect (pp. 1242, 1254). Outstanding olfactory abilities of individuals with visual impairments have repeatedly been reported in everyday life contexts. For instance, Julia Brace (James, 1890) and an anonymous young boy (Hinds, 1984) were able to sort the freshly washed linen of acquaintances by smell alone; Willetta Huggins was able to identify the color of fabrics according to the odor of the dyes (Gault, 1923). Describing children with visual impairments sniffing out objects, people, or themselves, Hinds (1984) interpreted these frequent behaviors as an unrestrained seeking of information. Odors seem to help build representations of the environment, as Rosenfeld (2001) also suggested. In Rosenfeld's survey, respondents with visual impairments declared more often than their sighted counterparts that odors provide useful information to characterize or identify places and people. These sparse observations stimulated us to investigate olfaction-blindness interactions in everyday settings. The purpose of our study was to conduct a pilot investigation of the self-reported awareness and reactivity to odors of children with visual impairments and sighted children. A questionnaire related to relevant everyday contexts involving food and social cues, as well as the general environment, was used to determine whether, and in which conditions, odors would constitute salient cues for children with visual impairments. METHOD Participants Six boys and two girls with visual impairments, aged 8 to 11, were recruited from a specialized center in Dijon, France (see Table 1 for the characteristics of the participants). …

Olfactory dysfunction in Parkinsonism caused by PINK1 mutations

Hyposmia is a common nonmotor feature of Parkinson's disease (PD) and has been variably detected in monogenic Parkinsonisms. To assess olfactory dysfunction in PINK1-related Parkinsonism, we evaluated olfactory detection threshold, odor discrimination, and odor identification in five groups of subjects: sporadic PD (n = 19), PINK1 homozygous (n = 7), and heterozygous (n = 6) parkinsonian patients, asymptomatic PINK1 heterozygous carriers (n = 12), and Italian healthy subjects (n = 67). All affected subjects and all healthy heterozygotes but one resulted hyposmic, with most patients in the range of functional anosmia or severe hyposmia. Detection threshold was more preserved and discrimination more impaired in patients with PINK1 mutations than in PD cases. Alterations of detection and discrimination were observed also in PINK1 asymptomatic heterozygotes. On the contrary, odor identification appeared to be mostly related to the disease status, as it was impaired in nearly all patients (including PD and PINK1 cases) and preserved in healthy heterozygotes. Our data indicate that olfactory dysfunction is common in PINK1 Parkinsonism and consists typically in defective odor identification and discrimination. A milder olfactory deficit, mostly involving discrimination, can be found in asymptomatic heterozygotes, possibly indicating an underlying preclinical neurodegenerative process.

Peripheral Olfactory System for Clinical and Basic Psychiatry: A Promising Entry Point to the Mystery of Brain Mechanism and Biomarker Identification in Schizophrenia

Peripheral Olfactory System for Clinical and Basic Psychiatry: A Promising Entry Point to the Mystery of Brain Mechanism and Biomarker Identification in Schizophrenia

SFGP 2007 - An Adsorption and Photocatalysis Study of Ethyl Hexanoate

Titanium dioxide photocatalysis is an emerging and very promising technology to reduce odorous industrial pollution. Using an adsorbent could offer an interesting way to enhance the pollutants photodecomposition rate. Our project deals with industrial emissions that contain a high concentration of esters such as ethyl hexanoate (EH) which has a very low olfactory detection threshold and it is very unpleasant both in industrial indoor air and in outer emission.Photocatalysis is performed here within a mixed flow reactor involving two fibrous media. The first one is a media coated with TiO2, SiO2 and zeolite and the second one is a mixture of TiO2, SiO2 and activated carbon (AC). A three-level full factorial design of experiments is performed with TiO2 – zeolite media. It permits us to determine the impact of two main parameters on adsorption and photocatalysis phenomena; moisture inflow (from 0 to 15 g.m-3) and pollutant concentration (from 50 to 150 mg/m3). Adsorption capacity ranges between 4 to 37 mg EH/g of media. It decreases while humidity increases due to competitive adsorption of water and pollutants on photocatalyst sites. Moreover the EH conversion rate increases when inlet concentration decreases. An optimal relative humidity can be deduced to reach an optimal conversion rate for a fixed inlet concentration. Conversion rate values of 24, 39 and 25 % are observed at respective humidity values of 0, 7.5 and 15 g.m-3 for a 100 mg/m-3 inlet concentration. The designs of the experiment are descriptive and predictive for adsorption capacity and degradation rates.With TiO2 – AC media, experiments are carried out at 15 g.m-3 of humidity and 100 mg/m3 of EH inlet concentration. As expected, a high-grade adsorbent media leads to a higher adsorption capacity compared with TiO2 – zeolite media (130 instead of 4 mg EH/g of media). Nevertheless, even if adsorption capacity is higher, conversion rate decreases (23 % instead of 46 %). Thus, in our experimental conditions, a very high content of adsorbent in the photocatalyst media does not improve the global degradation efficiency probably due to the lack of desorption of pollutants from AC.

Activation of olfactory and trigeminal cortical areas following stimulation of the nasal mucosa with low concentrations of S(-)-nicotine vapor--an fMRI study on chemosensory perception.

Applied to the nasal mucosa in low concentrations, nicotine vapor evokes odorous sensations (mediated by the olfactory system) whereas at higher concentrations nicotine vapor additionally produces burning and stinging sensations in the nose (mediated by the trigeminal system). The objective of this study was to determine whether intranasal stimulation with suprathreshold concentrations of S(-)-nicotine vapor causes brain activation in olfactory cortical areas or if trigeminal cortical areas are also activated. Individual olfactory detection thresholds for S(-)-nicotine were determined in 19 healthy occasional smokers using a computer-controlled air-dilution olfactometer. Functional magnetic resonance images were acquired using a 1.5T MR scanner with applications of nicotine in concentrations at or just above the individual's olfactory detection threshold. Subjects reliably perceived the stimuli as being odorous. Accordingly, activation of brain areas known to be involved in processing of olfactory stimuli was identified. Although most of the subjects never or only rarely observed a burning or painful sensation in the nose, brain areas associated with the processing of painful stimuli were activated in all subjects. This indicates that the olfactory and trigeminal systems are activated during perception of nicotine and it is not possible to completely separate olfactory from trigeminal effects by lowering the concentration of the applied nicotine. In conclusion, even at low concentrations that do not consistently lead to painful sensations, intranasally applied nicotine activates both the olfactory and the trigeminal system.

Test-Retest Reliability of the Olfactory Detection Threshold Test of the Sniffin' Sticks

The aim of the present study was to investigate the test-retest reliability of the olfactory detection threshold subtest of the Sniffin' Sticks test battery, if administered repeatedly on 4 time points. The detection threshold test was repeatedly conducted in 64 healthy subjects. On the first testing session, the threshold test was accomplished 3 times (T(1) = 0 min, T(2) = 35 min, and T(3) = 105 min), representing a short-term testing. A fourth threshold test was conducted on a second testing session (T(4) = 35.1 days after the first testing session), representing a long-term testing. The average scores for olfactory detection threshold for n-butanol did not differ significantly across the 4 points of time. The test-retest reliability (Pearson's r) between the 4 time points of threshold testing were in a range of 0.43-0.85 (P < 0.01). These results support the notion that the olfactory detection threshold test is a highly reliable method for repeated olfactory testing, even if the test is repeated more than once per day and over a long-term period. It is concluded that the olfactory detection threshold test of the Sniffin' Sticks is suitable for repeated testing during experimental or clinical studies.

Olfactory sensitivity for putrefaction-associated thiols and indols in three species of non-human primate

Using a conditioning paradigm, the olfactory sensitivity of four spider monkeys, three squirrel monkeys and three pigtail macaques to four thiols and two indols, substances characteristic of putrefaction processes and faecal odours, was assessed. With all odorants, the animals significantly discriminated concentrations below 1 p.p.m. (part per million) from the odourless solvent, and in several cases individual animals even demonstrated thresholds below 1 p.p.t. (part per trillion). The detection thresholds of 0.03 p.p.t. for indol in Saimiri sciureus and Macaca nemestrina and 0.96 p.p.t. for ethanethiol in Ateles geoffroyi represent the lowest values among the more than 50 odorants tested so far with these species and are in the same order of magnitude as the lowest detection thresholds reported so far in the rat and the mouse. The results showed (a) all three species of non-human primate to have a highly developed olfactory sensitivity for putrefaction-associated odorants, and (b) a significant correlation between perceptibility in terms of olfactory detection threshold and carbon chain length of the thiols, and a marked effect of the presence vs absence of a methyl group on perceptibility of the indols tested in two of the three species. The results support the hypotheses that (a) between-species differences in neuroanatomical or genetic features may not be indicative of olfactory sensitivity, and (b) within-species differences in olfactory sensitivity may reflect differences in the behavioural relevance of odorants.

Genetic Elucidation of Human Hyperosmia to Isovaleric Acid

The genetic basis of odorant-specific variations in human olfactory thresholds, and in particular of enhanced odorant sensitivity (hyperosmia), remains largely unknown. Olfactory receptor (OR) segregating pseudogenes, displaying both functional and nonfunctional alleles in humans, are excellent candidates to underlie these differences in olfactory sensitivity. To explore this hypothesis, we examined the association between olfactory detection threshold phenotypes of four odorants and segregating pseudogene genotypes of 43 ORs genome-wide. A strong association signal was observed between the single nucleotide polymorphism variants in OR11H7P and sensitivity to the odorant isovaleric acid. This association was largely due to the low frequency of homozygous pseudogenized genotype in individuals with specific hyperosmia to this odorant, implying a possible functional role of OR11H7P in isovaleric acid detection. This predicted receptor–ligand functional relationship was further verified using the Xenopus oocyte expression system, whereby the intact allele of OR11H7P exhibited a response to isovaleric acid. Notably, we also uncovered another mechanism affecting general olfactory acuity that manifested as a significant inter-odorant threshold concordance, resulting in an overrepresentation of individuals who were hyperosmic to several odorants. An involvement of polymorphisms in other downstream transduction genes is one possible explanation for this observation. Thus, human hyperosmia to isovaleric acid is a complex trait, contributed to by both receptor and other mechanisms in the olfactory signaling pathway.

Olfaction in patients with mild cognitive impairment and Alzheimer's disease

Understanding of olfactory dysfunction in Alzheimer's disease (AD) remains limited. In particular, it is not known how early in the course of the disease olfactory deficits occur, and whether they are restricted to identification or involve other aspects of olfaction. We studied olfactory (odor detection thresholds, quality discrimination, and identification) and cognitive (attention, reasoning, memory, naming and fluency) functioning in patients with AD, with mild cognitive impairment (MCI), and in normal elderly control (NEC) participants. MCI patients were impaired in olfactory sensitivity and identification, while a discrimination deficit was accounted for by abnormal thresholds. AD patients were impaired in all three domains, and were worse than the MCI group. Odor discrimination (OD) and identification performance correlated more prominently than detection thresholds with performance on neuropsychological tests. We concluded that deficits in olfactory detection thresholds and identification occur early in AD, before clinical symptoms are fully developed, and decline further over the course of the disease. High detection thresholds, together with impaired identification, may be useful as an early indicator of AD.