Odor Experience Research Articles

Fragrant mechanisms: The impact of odours — direct and indirect effects

Whilst many previous studies have reported the effects of individual variables on odour perception, very little work has been reported which identifies the contribution of each of these variables to the odour experience. Few investigators have considered how these different factors are related to one another. It is unclear, at this stage, whether indirect effects such as expectations, beliefs, and personality are interactive or whether there is a single factor underpinning all psychological factors. How then, is this of interest to aromatherapists? In the first instance, professional aromatherapists should be aware of how essential oils influence the individual they are treating. If it becomes evident that the application of essential oils to a client results in direct physiological changes then one needs to identify which oils will be suitable for the particular application required. This would provide a rather strict framework from which aromatherapists should work. However, should it be found that the effects of essential oils are largely indirect, or cognitive, by nature, then a much more relaxed structure of which oils are suitable could be employed. This would allow the aromatherapist to “negotiate” which oils a particular client would like used during their treatment. The future is uncertain at the moment, however from the evidence discussed in this article, it is likely that both direct and indirect effects influence how a particular essential oil will perform.

Perceptual Learning in Olfaction: Professional Wine Tasters versus Controls

By having professional wine tasters and controls perform olfactory tasks of absolute detection (1-butanol), discrimination (lemon and cloves), and identification (common household odors), the present two experiments studied (a) if perceptual odor learning takes place from odor experience acquired under nonlaboratory conditions, (b) if this learning generalizes to odors for which experience is limited, and (c) if generalized learning can be referred to increased general interest for odors that increases attention to odorous features. The results showed that whereas wine tasters were not better than controls on detection, they were superior to controls on discrimination and identification, the latter due to only a few odors. Ratings of experience with certain odors during professional evaluation suggest that generalized perceptual learning may take place in discrimination but not in identification. Wine tasters did not show more general interest for odorous features than did controls. The nonsuperiority in detection may be explained by the fact wine tasters have no professional experience of a detection task per se, implying that perceptual odor learning does not generalize from the olfactory tasks of discrimination and identification to detection.

Relationship between development of odor perception and language

The paper integrates the data on children's experience of odor and their inclination and ability to describe them verbally. Experimental data and questions about the validity of the earlier sensory methodology are reviewed along with the debate about whether children's odor preferences are learned or innate. The odor preference data are then evaluated linguistically. Attention is called to the meaning expressed in the one-word stage and in first sentences, particularly expression of attribute in early language development. A review of this literature reveals no evidence that young children express odor preferences. There are two possible reasons. One is the semantic/syntactic complexity of the verbe "to smell" demonstrated in research on the use of perceptual verbs in more than 50 languages. The other is the generally established fact that children 's early language reflects prior and salient experiences.

The role of learning in adult food location by the larval parasitoid,Microplitis croceipes (Hymenoptera: Braconidae)

Wind tunnel experiments were conducted to determine roles of odor learning in food foraging of the larval parasitoid,Microplitis croceipes (Hymenoptera: Braconidae). Females that had neither fed on sucrose water nor experienced any odor and females that had experienced an odor without feeding failed to respond to any odors in a wind tunnel. Most of the females that had fed without an odor also did not respond to odors. However, most of the females that had experienced an odor during feeding on sucrose water flew to the odor. These results indicate that when females experience an odor during feeding, they learn to associate the odor with food and subsequently respond to the odor. As age of females increased, their response to an experienced odor increased, peaked 2 to 5 days after emergence, and then decreased. With an increasing number of odor experiences while feeding, accuracy of females choosing the experienced odor increased. Females that experienced an odor while feeding three to five times chose the experienced odor 90% of the time. When females experienced an odor while feeding five times, the memory of food associated odor lasted at least 2 days. When they experienced food with two odors successively, they could memorize both odors, and multiple experiences did not cause memory interference. Even when females had learned a food-associated odor, their response to the learned odor ceased after several visits on patches containing the odor but no food. Such “negative experience” may cause switching of food searching to new odors by females.

Functional mapping of odor-activated neurons in the olfactory bulb.

Induction of immediate-early gene expression, in particular c-fos, can be used to map neural activity in many brain areas, including the olfactory system. By making use of the resolution provided by cellular localization of c-fos mRNA or Fos protein, those neurons activated by a particular odor stimulus can be identified. Odor presentation to awake rats increases c-fos expression by bulb neurons located in discrete portions of the glomerular layer and in the underlying mitral and granule cell layers. The translaminar distribution of co-ordinately activated cells corresponds to the 'functional unit' predicted by the synaptic organization of the bulb, and the distribution of these units throughout the bulb as a whole differs for different odors. The bulbar pattern of activity is spatially altered by changes in odor intensity and during the course of postnatal development. These findings support the idea that distributed patterns of odor-induced neuronal activity contribute to the encoding of olfactory information. Moreover, the role of c-fos in the transcriptional regulation of other genes suggests a mechanism whereby odor experience can lead to long-term changes in the olfactory system.

Chlordiazepoxide reduces the generalised anxiety, but not the direct responses, of rats exposed to cat odor

Rats were treated for 5 days with vehicle or chlordiazepoxide (CDP, 5, 10, or 20 mg/kg/day) and then exposed to a cloth impregnated with a neutral or cat odor. Those exposed to cat odor made significantly fewer contacts with the cloth and spent less time in contact with it and more time sheltering than those exposed to the neutral odor. CDP (5 mg/kg) significantly increased the time in contact with both odor cloths, but there were no other significant effects in the cat odor group. Rats previously exposed to cat odor showed significant anxiogenic responses in the social interaction and elevated plus-maze tests that were significantly reversed by CDP. There was no reduction in the responses to the cat odor on a second occasion as a result of the first exposure occurring after treatment with CDP (5 or 20 mg/kg). The anxiogenic effects of pentylenetetrazole (20 mg/kg) as detected in the social interaction and plus-maze tests were unaffected by prior odor experience. It is suggested that during exposure to the cat odor the responses of rats reflect avoidance components of a phobic anxiety state. Benzodiazepines are relatively ineffective against these responses in contrast to their efficacy against the generalised anxiety responses detected in the social interaction and plus-maze tests.

Low-dimensional chaos maps learning in a model neuropil (olfactory bulb).

Quantification of a chaotic system can be made by calculating the correlation dimension (D2) of the data that the system generates (Packard et al., 1980). The D2 algorithm, however, requires stationarity of the generator, a feature that biological data rarely reflect (Mayer-Kress et al., 1988). So we developed the "point correlation dimension" (PD2), an algorithm that accurately tracks D2 in linked data of different dimensions (Carpeggiani et al., 1991). We now present a mathematical argument that, for stationary data, individual PD2s converge to D2 and we demonstrate that the algorithm rejects contributions made by bursts of noise. Data were obtained from the surface of the olfactory bulb of the conscious rabbit (64 electrodes, 640 Hz each, 1.3 sec epochs) before and after presentation of a novel or habituated odor. D2 could be calculated in only 1 of 10 novel-odor trials, whereas PD2 could be calculated in all. Both algorithms indicated that a novel odor evokes a spatially uniform dimensional increase. The PD2 uniquely exhibited the dimensional decreases that occur during inspiration and the gradients of mean dimension present during the nonstimulated control state. These control gradients remained unchanged without odor experience, but showed spatially specific PD2 increases following odor habituation. It is interpreted that, 1) the PD2 is sensitive, accurate, and appropriate for dimensional assessment of biological data, 2) that during analysis of unfamiliar information a single global process is transiently evoked in the neuropil, and 3) after experience multiple spatially specific processes tonically map the sites of learning.

Norepinephrine-induced plasticity and one-trial olfactory learning in neonatal rats

The influence of norepinephrine (NE) on the acquisition of a conditioned odor preference and enhanced focal uptake of [ 14C]2-deoxyglucose (2-DG) within the olfactory bulb was assessed in neonatal rat pups. On postnatal day (PN) 6, pups were injected with either an NE receptor agonist (isoproterenol), NE receptor antagonist (propranolol or timolol), or saline before one-trial odor conditioning. The experimental conditioning group received a 10-min exposure to an odor (peppermint) and reinforcing tactile stimulation similar to that received from the dam. Control groups received only the odor, only the tactile stimulation, backwards presentation of the odor and tactile stimulation or neither of these stimuli. The next day, pups were either tested for an olfactory preference (Expts. 1 and 2) or assessed for differential olfactory bulb activity using the 2-DG technique (Expt. 3). The results indicate that early odor experience with either tactile stimulation or isoproterenol is sufficient to produce a learned behavioral preference and enhanced focal 2-DG uptake within the olfactory bulb. Moreover, an NE receptor blocker injected prior to training with odor and tactile stimulation blocks the acquisition of both behavioral preference and the enhanced 2-DG uptake. In Expt. 4, the effects of tactile stimulation and isoproterenol were further assessed. An odor paired with a moderate level of either of these stimuli produces learning. However, the simultaneous presentation of a moderate level of these stimuli paired with an odor does not result in an odor preference. An odor preference may be reinstated by simultaneous presentation of these stimuli, provided the level of each of these stimuli is too low to produce an odor preference when presented alone with an odor. These data suggest that exogenous NE and tactile stimulation are additive in their effect on learning. These results are discussed in terms of the neural mechanisms underlying reinforcement in infant rats.

The influence of early odour experience on the neural response of the olfactory bulb in laboratory mice.

In mice (strain NMRI) the influence of olfactory rearing conditions on the ontogenetic development of the bulbar electroencephalogram (EEG) was investigated. The cages of control animals were perfused continually with filtered air, whereas in the three experimental groups geraniol was added to the atmosphere at different times (group G0-13, from birth till day 13; group G0-6, from birth till day 6; group G6-12, from day 6 till day 12). At various ages the EEG of the bulbus olfactorius was studied by means of permanently implanted tungsten electrodes, and the neural response to nest odour and geraniol (10(-2) vol. %) was recorded. No differences were found between the groups regarding the overall development of the bulbar EEG, nor did the raising conditions affect the neural response to nest odour. However, in groups G0-13 and G6-12 a marked response to the odour of geraniol was recorded, while in the controls and the individuals that had experienced geraniol only during their first week of life, the bulbar response to this odourant did not differ from that obtained following stimulation with clean air. In the animals of group G0-13, which were investigated as adults (day 70), the prominent geraniol response was still recordable 2 months after the last contact with the odour. These results indicate that odours experienced during a sensitive period in the nest evoke neuronal alterations in the olfactory system of the mouse that facilitate processing of a known odourant.

Dependence of single unit activity in the olfactory bulb on early odor experience in the laboratory mouse

Dependence of single unit activity in the olfactory bulb on early odor experience in the laboratory mouse

Glycogen phosphorylase activity in the olfactory bulb of the young rat

The activity of glycogen phosphorylase, the enzyme that controls glycogen breakdown, was histochemically mapped in the olfactory bulbs of 19-day-old rats. The effect of early odor experience on subsequent olfactory bulb phosphorylase activity was also examined. The highest level of phosphorylase staining in the bulb (and seemingly the highest in the brain) was in the glomerular layer, followed by the external plexiform, internal plexiform, granule cell, and olfactory nerve layers. Virtually no activity was visible in the large output neurons of the bulb, mitral, and tufted cells. Early peppermint odor experience, previously shown to increase metabolic activity in specific glomerular foci as measured by 2-deoxyglucose uptake, had no apparent effect on glomerular-layer phosphorylase activity. In some odor-familiar animals, however, patches of activity were seen in the internal plexiform layer in the area of the bulb where foci of high deoxyglucose uptake are seen in response to peppermint. The patches were directly in line with modified glomerular clusters often seen to underlie foci of enhanced deoxyglucose uptake. The existence of particularly heavy activity in the peripheral third of the glomerular layer, where glycogen-containing modified Schwann cells have been localized, raises the possibility that the glomerular-layer activity is at least partially glial in origin. Finally, because of its rich noradrenaline and serotonin innervation and high density of insulin receptors, the olfactory bulb is proposed as a model system to study the interaction of glycogen/glucose metabolism with neural activity in a relatively well-defined neuronal circuit.

Correlates of Anxiety, Taste and Odor Experiences in Chemotherapy Cancer Patients

Abstract Fifty cancer patients undergoing chemotherapy were studied with respect to the following variables: (1) Anxiety, nausea, and vomiting before, during, and after chemotherapy administration; (2) Treatment-related taste and odor sensations experienced outside the treatment setting; and (3) Responses to the Autonomic Perception Questionnaire (APQ). Patients reporting taste and odor experiences plus anxiety before chemotherapy (Group TOA) were significantly more likely to experience anticipatory nausea and vomiting than patients reporting either (TO/A) or none of these (NIL). TOA patients also scored higher on the APQ than NIL patients. Taste/odor sensations reminding of chemoterapy treatment, but experienced outside the treatment setting are suggested as a measure of individual “ease of conditioning” in cancer patients.

Do infusion-related tastes and odors facilitate the development of anticipatory nausea? A failure to support hypothesis.

Distinctive tastes and odors have been identified as potent nausea-eliciting stimuli in cancer chemotherapy patients who develop anticipatory nausea or vomiting (ANV). Based on the experimental research on illness-aversion learning and based on previous clinical research with chemotherapy patients, it was hypothesized that the presence of tastes and odors during infusions should increase the likelihood that a patient will subsequently develop ANV. Seventy-eight new chemotherapy outpatients were interviewed immediately following each of their infusions with regard to the experience of infusion-related tastes, odors, and body sensations. Results failed to support the hypothesis. The subsequent development of ANV was unrelated to reports of tastes and odors both during patients' initial two chemotherapy infusions and during the two infusions preceding their initial report of ANV. Furthermore, reports of tastes and odors were surprisingly infrequent relative to previous research. Methodological and environmental explanations for this difference in taste and odor prevalence are considered. It is concluded that, when present, infusion-related tastes and odors may indeed increase the likelihood of subsequent development of ANV. However, future research should examine the extent to which the physical characteristics of chemotherapy clinics might affect the prevalence of infusion-related tastes and odors.

Alcohol drinking patterns of young adult rats as a function of infantile aversive experiences with alcohol odor

Recent studies have demonstrated that in the rat, alcohol intake patterns can be regulated by prior experiences with the odor of this drug. The efficacy of such regulation appeared to be limited to early postnatal stages of development. The present study supports the possibility, however, that early ethanol odor experiences are retained over considerable amounts of time and may play an effective role in the control of adult patterns of alcohol ingestion. Specifically, it was observed that rats exposed to pairings of ethanol odor and lithium chloride toxicosis (Etoh-LiCl group) during Postnatal Days 5, 10, 15, and 20 displayed as young adults (52-58 days) significant decreases in voluntary alcohol intake scores. This decrease was determined relative to control rats that had been safely exposed to ethanol odor (Etoh group) or given only lithium toxicosis but no ethanol odor (LiCl group) during Postnatal Days 5, 10, 15, and 20. Relative to these controls (Etoh and LiCl groups) the experimental subjects (Etoh-LiCl group) also exhibited significant decreases in their adult preference for ethanol odor, as assessed through an olfactory locational test. The present results indicate several ways in which conditioned aversion to ethanol intake may arise and imply that the transfer between olfactory and gustatory aversions takes place at the time of memory storage rather than at some later stage of memory processing. In a more general sense, the present results add to others in our series to support the notion that consideration of the effects of early experience with alcohol may aid in the clarification and control of voluntary alcohol intake patterns.

Odor specificity of the enhanced neural response following early odor experience in rats

The enhanced neural response in the olfactory bulbs of rat pups following early olfactory experience is specific to the familiar odor. Pups were exposed daily to either peppermint or cyclohexanone odor for the first 18 postnatal days. On day 19, peppermint-familiar pups exposed to peppermint had significantly higher [ 14C]2-deoxyglucose (2-DG) uptake in a focal glomerular area compared with the response to peppermint by cyclohexanone-familiar pups. We also found that cyclohexanone-experienced pups had a subsequent enhanced response to cyclohexanone odor in glomerular areas medial and caudal to those responding to peppermint. None of the 2-DG uptake differences were attributable to respiration differences between the groups during any part of the odor test.

Enhanced neural response by adult rats to odors experienced early in life

The enhanced olfactory bulb neural response to familiar odors by young rats persists into adulthood. Ninety-day-old rats who had received neonatal odor exposure had an enhanced uptake of [14C]2-deoxyglucose (2-DG) when exposed to the familiar odor. The odor-familiar rats did not have an increased respiration rate during the 2-DG test. A long-lasting change in neuronal response is consistent with the observation of behavioral effects of early odor experience persisting into adulthood.

Olfactory bulb responses after odor aversion learning by young rats

The increased olfactory bulb response by young rats to familiar odors was not observed in response to odors which have attained their familiarity in aversive situations. Odor experience associated with toxicosis induced a behavioral aversion to the odor which was not accompanied by the enhanced uptake of [ 14C]2-deoxyglucose (2-DG) that accompanies attractive familiar odors. A single odor exposure on day 17 was sufficient to induce a small increase in 2-DG uptake in specific glomerular areas. We hypothesize that a different neural substrate underlies familiarity associated with an aversive odor than that associated with an attractive odor.

Ultrasonic vocalizations by male house mice (Mus musculus) to novel odors: Roles of infant and adult experience.

Two experiments were conducted to examine 70-kHz ultrasonic courtship vocalizations by adult male mice (Mus musculus) to novel odors following exposure to these odors in infancy and/or adulthood. The research was performed in hopes of better understanding the experiences giving rise to vocalizations to naturally occurring chemosignals. Experiment 1 demonstrated that adult males normally do not vocalize to the urine of female rats but would come to do so if adult female mice odorized with female rat urine were repeatedly encountered postpubertally. On the other hand, encountering their own mother odorized with female rat urine from birth until weaning did not promote vocalizations to the urine of female rats. Experiment 2 was designed to examine vocalizations to the urine of female mice whose urinary odor was altered by the ingestion of fenugreek, a spice. Although the magnitude of the effect was smaller in this experiment, greater amounts of vocalization again were seen by males that as adults encountered females that had ingested fenugreek. Males with such experience also showed a small but significant elevation in vocalizations to the fenugreek odor itself. Again, experience with the novel odor during infancy was not associated with elevated vocalizations during adulthood either to fenugreek-altered urine or to the fenugreek odor itself. Thus vocalizations to two different novel odors occurred only after an adult male had encountered an adult female odorized with the novel odor. On the other hand, none of the novel odor experiences eliminated vocalizations to the naturally occurring chemosignal in female mouse urine.(ABSTRACT TRUNCATED AT 250 WORDS)

Preference for natural odors in rat pups: Implications of a failure to replicate

The results of the present experiment indicate that very minor changes in the diet on which a rat dam is maintained can have profound effects on the attractiveness of her feces to her pups. Rat pups exhibited a strong preference for the odor of feces taken from dams maintained on one sample of Purina Rodent Laboratory Chow No. 5001, but no preference for the odor of the feces of dams maintained on a second sample of the same diet. These data point to the need for very great care in the design of experiments employing, as independent variables, stimuli which are not under direct experimenter control. The results also suggest that experience of a natural odor during ontogeny may not be sufficient for the development of a preference for that odor in young rats.

Intranasal trigeminal stimulation from odorous volatiles: Psychometric responses from anosmic and normal humans

Psychometric ratings of the perceived intensity, pleasantness, coolness, warmth, and presumptive safety of high concentrations of 47 nasally-inhaled chemicals commonly used in olfactory research were established for three groups of human observers (n = 15/group): (1) anosmics lacking olfactory (CN I), but not trigeminal (CN V), nerve function; (2) normals asked to rate only intranasal trigeminal (CN V) sensations (trigeminal focus group); and (3) normals asked to rate the overall odor experience in the traditional fashion. Forty-five of the 47 compounds were detected by at least some proportion of the anosmics in a forced-chice test. Although differences in the rated intensities of the stimuli were present between the three experimental groups, the relative rankings of the intensity responses were quite similar (rs ranging from 0.92 to 0.97). The pleasantness and presumed safety of the chemicals varied inversely with the perceived intensity in all three groups. The use of 11 to 13 readily-available and computer-derived molecular descriptors in linear learning machine pattern recognition analyses separated the 47 stimuli correctly into four discrete intensity classes. A multiple linear regression equation based upon such molecular descriptors (multiple R = .88) proved successful in predicting the perceived trigeminal intensities of 12 chemical stimuli similar in general structure to members of the original stimulus set (r = .80 between predicted and observed intensities). These results emphasize the importance of trigeminal input in human nasal chemoreception and support the notion that the perceived intensities of nasally-inhaled stimulants can be mathematically predicted from relatively simple physicochemical and molecular structural parameters.