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PubMed1997

Application of statistical thermodynamics to the olfaction mechanism.

The application of the grand canonical ensemble in statistical thermodynamics to the stimulus adsorption on the olfactory receptor sites, assuming some simplifying hypotheses, leads us to an expression of the olfactory response R, which is a function of various physico-chemical parameters involved in the olfaction mechanism, e.g. the stimulus concentration, the saturated vapor pressure, the power law exponent and the partition coefficient. This expression of R is in agreement with the olfactory response of the Hill model, but is more explicit. Stevens' law and the olfactory threshold expression are easily deduced from R. The expression of the threshold we established from R enabled us to explain some empirical relations in the literature between the parameters quoted above. The use of the grand canonical ensemble with the chemical potential notion gave us an interpretation of Stevens' law and a better understanding of the role of some parameters involved in the olfaction mechanism, such as saturated vapor pressure and power law exponent.

Adsorption↗
PubMed2006

Cross-modal interactions between olfaction and vision when grasping.

This study used kinematics to investigate the integration between vision and olfaction during grasping movements. Participants were requested to smell an odorant and then grasp an object presented in central vision. The results indicate that if the target was small (e.g., a strawberry), the time and amplitude of maximum hand aperture were later and greater, respectively, when the odor evoked a larger object (e.g., an orange) than when the odor evoked an object of a similar size as the target or no odor was presented. Conversely, the time and amplitude of maximum hand aperture were earlier and reduced, respectively, when the target was large (e.g., a peach) and the odor evoked a smaller sized object (e.g., an almond) than when the odor evoked an object of a similar size as the target or no odor was presented. Taken together, these results support the evidence of cross-modal links between olfaction and vision and extend this notion to goal-directed actions.

Adult↗
PubMed2005

Functional magnetic resonance imaging study of human olfaction and normal aging.

BACKGROUND: The function of human olfaction declines with advancing age. An important question centers on whether functional alterations to olfactory brain structures accompany age-related behavioral changes. In the present study, we tested the hypothesis that aged adults have intact though reduced activity in the central olfactory system using functional magnetic resonance imaging (fMRI). METHODS: University of Pennsylvania Smell Identification Test (UPSIT) was used to test the smell function of 11 young (23.9 +/- 1.6 years) and 8 aged (66.4 +/- 4.4 years) healthy participants. Then, the participants received fMRI at 3.0 T with lavender and spearmint as stimulants. After fMRI, the participants provided ratings for the odorants' intensity and pleasantness. RESULTS: The average UPSIT score of the aged adults was 34.1 +/- 1.5, which was significantly lower than that of the young adults (37.3 +/- 1.1) (p =.0004). Both age groups showed significant activation in major olfactory brain structures, including the primary olfactory cortex, entorhinal cortex, hippocampus and parahippocampal cortex, thalamus, hypothalamus, orbitofrontal cortex, and insular cortex and its extension into the inferior lateral frontal region. The aged adults showed less brain activity in olfactory structures (p =.022), consistent with lower ratings of odor intensity and UPSIT scores. Activation intensity in bilateral primary olfactory cortex areas and right insular cortex was also comparatively weaker (p <.019). CONCLUSION: Results demonstrate that significant activation in aged adults can be observed in all the olfactory brain structures that are activated in young adults, but with lower activation volume and intensity. This finding provides a necessary baseline for further investigations in olfaction and aging.

Adult↗
PubMed1998

Spatiotemporal masking in pure olfaction.

In olfaction, it is not possible to determine which nostril is being stimulated, i.e., lateralize, when a pure olfactory substance, e.g., phenylethyl alcohol or vanillin, is administered into one nostril, and, simultaneously, an odorless, solvent blank into the contralateral nostril. We subjected volunteers to extensive training, with feedback on each trial, in an attempt to determine whether it was possible, in these well-trained subjects, to overcome this apparent impossibility. We failed to obtain any evidence to support the notion that a pure olfactory stimulus could be lateralized when the odorant and blank were presented simultaneously. The task, however, became simple when the odorant and the blank entered each nostril sequentially. We investigated, using a two-channel olfactometer, temporal parameters that enabled such discrimination. We controlled the duration of odorant and blank air puffs, as well as their mutual timing, to determine the threshold stimulus onset-disparity, i.e., the interval between stimulus onset and blank onset, that resulted in an inability to lateralize. Latencies shorter than the threshold interval would be perceived as simultaneous stimulation. We determined that the onset interval was between 200 and 400 ms, depending on the duration of the stimuli (a shorter interval was noted for stimuli of 150-ms duration relative to 300- and 450-ms stimuli). This was also true when two odorants were applied, rather than an odorant and a blank, and the subject was instructed to focus on the sequence of odorant delivery and side of stimulation. The temporal onset threshold was the same for lateralization and for order of stimulation. Whether the olfactory system per se mediates this discrimination or whether inputs from olfaction and chemesthesis, via trigeminal free nerve endings stimulated by air-stream onset, combine to allow this discrimination has yet to be determined.

Evoked Potentials↗
PubMed2005

Microsurgical anatomic features of the olfactory nerve: relevance to olfaction preservation in the pterional approach.

OBJECTIVE: The pterional approach represents the standard approach for most lesions of the anterior and middle cranial fossa. It requires some degree of frontal lobe retraction, which may result in temporary or permanent damage of olfaction because of nerve avulsion or mechanical compression. The purpose of this study, based on microanatomic dissection of human cadaveric specimens, was to review the microsurgical anatomic features of the nerve and suggest operative nuances that may contribute to reducing the rate of postoperative olfactory dysfunction. METHODS: Twenty olfactory nerves and tracts were examined in 10 human cadaveric heads obtained from three fresh and seven formalin-fixed adult cadavers. A standard pterional craniotomy was performed. The olfactory nerve was dissected from its arachnoidal envelopes and then mobilized for an average length of 30 mm (range, 25-35 mm). RESULTS: The possible retraction of the frontal lobe was 10 to 15 mm. More retraction invariably resulted in nerve disruption. CONCLUSION: The standard sylvian and basal cistern opening may be insufficient to guarantee preservation of olfactory function. Early identification and arachnoidal dissection of the nerve may reduce the rate of olfaction compromise. The opening of the subarachnoidal space should be performed in a proximal-to-distal manner to allow early visualization of the olfactory bulb and its dissection. The arachnoidal dissection should be performed with sharp instruments, avoiding any traction on the posterior portion of the olfactory tract. Any direct retractor compression should also be avoided to spare the microvasculature lying on the dorsal surface of the nerve.

Cadaver↗
PubMed2004

A network of stimulatory and inhibitory Galpha-subunits regulates olfaction in Caenorhabditis elegans.

The two pairs of sensory neurons of C. elegans, AWA and AWC, that mediate odorant attraction, express six Galpha-subunits, suggesting that olfaction is regulated by a complex signaling network. Here, we describe the cellular localization and functions of the six olfactory Galpha-subunits: GPA-2, GPA-3, GPA-5, GPA-6, GPA-13, and ODR-3. All except GPA-6 localize to sensory cilia, suggesting a direct role in sensory transduction. GPA-2, GPA-3, GPA-5, and GPA-6 are also present in cell bodies and axons and GPA-5 specifically localizes to synaptic sites. Analysis of animals with single- to sixfold loss-of-function mutations shows that olfaction involves a balance between multiple stimulatory and inhibitory signals. ODR-3 constitutes the main stimulatory signal and is sufficient for the detection of odorants. GPA-3 forms a second stimulatory signal in the AWA and AWC neurons, also sufficient for odorant detection. In AWA, signaling is suppressed by GPA-5. In AWC, GPA-2 and GPA-13 negatively and positively regulate signaling, respectively. Finally, we show that only ODR-3 plays a role in cilia morphogenesis. Defects in this process are, however, independent of olfactory behavior. Our findings reveal the existence of a complex signaling network that controls odorant detection by C. elegans.

Animals↗
PubMed2002

Insect pheromone olfaction: new targets for the design of species-selective pest control agents.

Insects communicate extensively with chemical signals specific to their species (pheromones). The highly sensitive and selective olfactory system involved in detection of these signals has attracted attention as a target for the design of novel pest control agents. This review summarizes efforts in understanding the structure-activity relationships of pheromone olfaction and in the design of compounds that selectively interfere with transport, recognition and degradation of pheromones in the peripheral olfactory system. Pheromone olfaction inhibitors are potential environmentally benign insect control agents.

Animal Communication↗
PubMed1992

Relative importance of vision and olfaction for detection of estrus by bulls.

The objective of this experiment was to determine the relative importance of olfaction and visual observation of heifer mounting behavior to the detection of estrus by bulls. An observation pen was designed to allow the evaluation of the preference of five sexually experienced bulls under three sets of stimuli. The observation pen was 4 m x 17 m with a smaller enclosure (2 m x 4 m) at each end that housed either a pair of heifers in diestrus (D), a pair of heifers in estrus that were allowed to mount one another (EM), or a pair of heifers in estrus that were separated by an aluminum panel to prevent mounting behavior (E). The preference of bulls was determined between EM heifers compared to D heifers, EM heifers compared to E heifers, and E heifers compared to D heifers. Each bull was individually allowed 5 min inside the observation pen to demonstrate its preference. Preference was defined as the total time that bulls spent within 2.5 m of either pair of heifers. Each bull was subjected to 10 observation periods of each set of stimuli during a 4-mo period. Bulls preferred to be near EM heifers compared with either E or D heifers (P less than .05). However, the bulls demonstrated no preference (P greater than .05) for E heifers compared with D heifers. These data indicate that when physical contact is denied, bulls use visual observation of female homosexual behavior as the primary indicator of estrus and that olfaction alone provides insufficient stimuli for bulls to indicate preference toward heifers in estrus compared with heifers in diestrus.

Animals↗
PubMed1999

A technique for assessing the effects of olfaction on feed preference in lactating Holstein cows.

Our objective was to develop a method for assessing the effects of olfaction on feed preference. Two multiparous lactating Holstein cows were offered a totally mixed ration consisting of corn silage, alfalfa haylage, and a ground corn and soybean meal-based concentrate mixture (25:25:50 on a DM basis) for their ad libitum consumption in four consecutive 2.5-h periods daily for 5 d. An apparatus was developed that allowed odorants to be distributed at a set rate over two feeding containers with limited possibility of odor carryover. Four odorants and a control (no odorant) were compared against each other. All possible comparisons were conducted on the left and right feeding sides to avoid potential lateral-preference effects. Rank values of 0 or .5 were assigned to each odorant based on the percentage of total feed consumed in a period. A test of overall equality based on the sums of squares of ranks was used to determine whether odors affected preference. The limited results indicated that inhalation of odorants did not affect preference. Rank values were doubled for several odorants when compared with others, which suggested that the sample size limited experimental sensitivity. To attain reasonable power, we estimated that at least six cows were needed per study. Large effects of odorants on feed preference would have been required to reach statistical significance in this trial; however, the method provides a practical technique for testing the effects of olfaction on feed preference in cattle when the suggested number of cows is used.

Animal Feed↗
PubMed2003

Olfaction as a traumatic reminder in posttraumatic stress disorder: case reports and review.

BACKGROUND: Memory for odors that are associated with intense emotional experiences is often strongly engraved. Odors are claimed to be more closely connected to affect than other sensory experiences. They can serve as potent contextual cues for memory formation and emotional conditioning and can also serve as cues for olfactory flashbacks. Though trauma-related smells have long been noted by clinicians to be precipitants of traumatic memories in patients with posttraumatic stress disorder (PTSD), very few reports have been published that document this. CASE REPORTS: We review olfactory memories and olfactory flashbacks by presenting 3 cases that illustrate the role of olfaction in PTSD. In these cases olfaction is either a precipitant of PTSD symptoms or an important component of reexperiencing. DISCUSSION: In PTSD, seemingly nonspecific cues have the potential to precipitate traumatic memories with strong emotional components. These conditioned responses in PTSD are hypothesized to be mediated by specific brain areas, i.e., amygdala, hippocampus, and orbitofrontal cortex. Questions about smells as a traumatic reminder should be part of the routine assessment of intrusive memories in PTSD. In addition, smells may have the potential to provide cues to exposure situations in therapy or to facilitate de novo conditioning.

Adult↗
PubMedDate not supplied

Evidence for gender-specific associations between leptin and olfaction.

BACKGROUND: The adipocyte-derived hormone leptin regulates food intake by stimulation of the long leptin receptor isoform in the hypothalamus. The long leptin receptor is also expressed in the piriform cortex, an area involved in the relay of olfactory cues. In rodents, both olfaction and leptin influence food seeking. OBJECTIVE: To examine whether serum leptin levels are associated with olfaction in humans. SUBJECTS: Two distinct samples were analyzed. The population-based sample, 60 men and 61 women, was randomly selected from a population living in Mölndal, Sweden. The obese sample, 31 men and 27 women, was from the ongoing Swedish Obese Subjects (SOS) study. METHODS: Olfactory function was assessed with a two-part test used at Connecticut Chemosensory Clinical Research Center. RESULTS: In the population-based sample, multiple regression analysis revealed a gender difference (interaction gender x leptin; P = .016) between the association of odor identification and logarithmically transformed (log) leptin when adjusting for smoking and log body mass index (BMI). In men the association was positive (beta = 13.2; P = .0026), whereas in women it was negative (beta = -11.4; P = .050). When further adjusting for the influence of menopause and estrogen treatment, the negative association between odor identification and leptin became stronger for women in the population-based sample (beta = -13.7; P = .027). In the obese sample, the associations were similar in direction to those observed in the population-based sample, although nonsignificant. CONCLUSION: Serum leptin levels were associated with odor identification in a randomly selected population. The association was gender-specific and independent of BMI. High odor identification scores were associated with high serum leptin levels in men and low serum leptin levels in women. This provides further support for previously recognized gender differences in the leptin system and suggests alternative ways for leptin to modulate its effects.

Adipose Tissue↗
PubMed1978

Olfaction in health & disease.

The significance of olfaction is frequently overlooked by health professionals. The purpose of this presentation is to briefly review the neurophysiology of olfaction, survey the relevant research, and present specific implications for occupational therapists working in both physical disabilities and psychiatric settings.

Adult↗
PubMed1996

Cross-modal correspondence between vision and olfaction: the color of smells.

Cross-modal sensory correspondences between vision and audition have been well described, but those between vision and olfaction have not. In Experiment 1, a method previously used to relate color names, mood names, and line elements was replicated and extended to describe odors by color. Significant color characterizations were found for all 20 test odors. Test-retest correlations showed color-odor correspondences to be as stable as nonodor measures after 2 years. In Experiment 2, new subjects matched Munsell color chips to the test odors. Thirteen odors had characteristic hues; there was significant variation in chroma and value. The selected Munsell hues corresponded to the color names endorsed in Experiment 1. Together, these experiments suggest the existence of robust correspondences between vision and olfaction.

Adolescent↗
PubMed1997

OSM-9, a novel protein with structural similarity to channels, is required for olfaction, mechanosensation, and olfactory adaptation in Caenorhabditis elegans.

Although cyclic nucleotide-gated channels mediate sensory transduction in olfaction and vision, other forms of sensory transduction are independent of these channels. Caenorhabditis elegans cyclic nucleotide-gated channel mutants respond normally to some olfactory stimuli and to osmotic stimuli, suggesting that these chemosensory responses use an alternative sensory transduction pathway. One gene that may act in this pathway is osm-9, which is required for each of these responses as well as a mechanosensory response to nose touch. osm-9 encodes a protein with ankyrin repeats and multiple predicted transmembrane domains that has limited similarity to the Drosophila phototransduction channels transient receptor potential (TRP) and TRP-like (TRPL). The sequence of OSM-9 and other TRP-like genes reveals a previously unsuspected diversity of mammalian and invertebrate genes in this family. osm-9 is required for the activity of the predicted G-protein-coupled odorant receptor ODR-10, which acts in the AWA olfactory neurons; its similarity to other G-protein-regulated transduction channels suggests that OSM-9 is involved in AWA signaling. osm-9:: GFP fusion genes are expressed in a subset of chemosensory, mechanosensory, and osmosensory neurons. osm-9 also affects olfactory adaptation within neurons that require the cyclic nucleotide-gated channel for olfaction; in these neurons, the gene has a regulatory function and not a primary role in sensory transduction.

Adaptation, Physiological↗
PubMed2000

Rehabilitation of olfaction after laryngectomy by means of a nasal airflow-inducing maneuver: the "polite yawning" technique.

OBJECTIVE: To develop a nasal airflow-inducing maneuver and apply it in the olfactory rehabilitation of patients who have undergone laryngectomy. DESIGN: Intervention study; before-and-after trial. SETTING: National cancer center. PATIENTS: Forty-four patients who underwent laryngectomy; 34 men and 10 women; mean age, 64 years (range, 42-80 years); mean time since surgery, 6 years (range, 8 months to 18 years). INTERVENTION: In a prospective clinical intervention study, we assessed the effectiveness of a nasal airflow-inducing maneuver ("polite yawning," ie, yawning with closed lips). Speech therapists trained the patients in the maneuver, and its effectiveness in inducing nasal airflow was checked with digital and water manometers. MAIN OUTCOME MEASURES: Olfactory acuity was assessed before and after the intervention by means of an odor detection test and a structured questionnaire concerning olfaction, taste, and appetite. Patients were categorized as "smellers" and "nonsmellers" on the basis of the results of the odor detection test and the present odor perception scale derived from the questionnaire. RESULTS: The nasal airflow-inducing maneuver could be taught to all patients, mostly in only one 30-minute therapy session. Fifteen of the 33 patients in the pretreatment nonsmeller category converted to smellers, for a success rate of 46% (P<.001). CONCLUSION: The nasal airflow-inducing maneuver (the "polite yawning" technique) allowed almost half of the patients to recover their sense of smell.

Adult↗
PubMed2003

Olfaction and social drive in schizophrenia.

BACKGROUND: The neurobiology of social dysfunction in schizophrenia is unknown, but smell identification deficits (SIDs) exist in schizophrenia, and olfaction is related to social affiliation in other mammals. The SIDs have been linked with negative symptoms and the deficit syndrome, but any specificity of SIDs for social dysfunction is unstudied. Low intelligence might explain this relationship, if it is associated with both negative symptoms and SIDs. We examined whether SIDs in schizophrenia were related broadly to negative symptoms, as are a number of other neuropsychological measures, or whether they might show a more specific relationship with social drive. METHODS: Smell Identification Test scores, Wechsler Adult Intelligence Scale-Revised IQ, symptomatology assessed with the Positive and Negative Syndrome Scale, and the deficit syndrome were determined in 70 patients with DSM-IV schizophrenia. RESULTS: The SIDs were related to negative symptoms and the deficit syndrome, but the association of SIDs with diminished social drive explained both relationships. Smell identification was also related to Wechsler Adult Intelligence Scale-Revised IQ, but intelligence was independent of the relationship of SID and social drive. The worse Smell Identification Test scores in male patients were attributable to a greater preponderance of men with the deficit syndrome. CONCLUSIONS: These analyses demonstrated independent relationships of Smell Identification Test scores to social drive and intelligence that together accounted for almost 50% of the variance in Smell Identification Test scores. There may be common neural substrates for the low social drive and SIDs in schizophrenia.

Drive↗
PubMed2002

Disabling disturbance of olfaction in a dental technician following exposure to methyl methacrylate.

It is often difficult to diagnose dysosmia due to occupational olfactotoxic substances. The authors present a case of disabling disturbance of olfaction in a dental technician. This is very likely to have been caused by exposure to methyl methacrylate. From 1988-1992, the dental technician had very extensive and sustained contact with a self-polymerizing acrylic resin based on methyl methacrylate. Her perception of smell was still normal in 1988, but it deteriorated up to 1992. The olfactory disorders have persisted and impede social life and occupational rehabilitation.

Dental Technicians↗
PubMed2007

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.

Aged↗