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PubMed1975

Olfaction in the development of social preferences in the human neonate.

Olfactory perception in the human neonate has been largely ignored. The present experiments examine the possibility that neonates can use smell to locate a food source and that they can differentiate between their own mother and another mother on the basis of smell. Head-turning to breast pads was used in perference tests. Although the neonate did not appear to be able to use smell to localize a food source, significantly more babies spent more time turning towards their own mother's breast pad than towards a clean breast pad at five days of age. By six days of age babies were showing a differential response between their own mother's breast pad and another mother's breast pad, although this differentiation was not present at two days of age.

Age Factors↗
PubMed2004

Passive perception of odors and semantic circuits.

The sense of smell has been traditionally assumed to be different from other sensory modalities in that odors are encoded perceptually, without a semantic component. Recent findings of improved odor memory upon encoding with verbal cues question this view. Furthermore, familiar odors are easier to remember and discriminate than are unfamiliar ones, and odor familiarity is reported to predict odor naming. To investigate whether familiar odors are processed by different cerebral structures than those that process unfamiliar odors, (15)O H(2)O-positron emission tomography (PET) measurements of cerebral blood flow were carried out in 14 healthy men. The task was passive, birhinal, smelling of familiar odors (FAM), unfamiliar odors (uFAM), and odorless air (AIR). Significant activations (P < 0.05) were calculated using the contrasts FAM-AIR, uFAM-AIR, and FAM-uFAM, and deactivations running these contrasts in the opposite direction. In relation to AIR, both FAM and uFAM activated amygdala, piriform cortex, and parts of anterior cingulate cortex. FAM activated, in addition, left frontal cortex (Brodmann's areas 44,45,47), left parietal cortex incorporating precuneus, and right parahippocampus. Clusters covering parahippocampus and precuneus were observed also in FAM-uFAM. The activation of left frontal cortex and right parahippocampus was positively correlated with familiarity ratings. Smelling of familiar but not unfamiliar odorants seems to engage cerebral circuits mediating memory and language functions, in addition to the engagement of olfactory cortex. Already the most elemental form of odor processing, passive perception thus seems to engage semantic circuits. This is achieved by the ability of odorants to immediately elicit associations and judgments of odor characteristics.

Adult↗
PubMed2005

Basic and clinical aspects of olfaction.

Disturbances of olfaction are a common occurrence in many neurological and neurosurgical patients and their correct diagnosis might be helpful in management and enhancement of quality of life. However, olfaction is seldom checked in most neurosurgical units and the "smell bottles" are often either absent or out of date. This chapter reviews systematically recent advances in our understanding of the anatomy, physiology (olfactory coding) and measurement of olfactory function in the human. The causes and symptoms of smell disorders, risk of damage to the olfactory system by various surgical procedures and, finally, the natural history of recovery and treatment of smell disorders, for example after trauma, are discussed.

Animals↗
PubMedDate not supplied

Sick-building syndrome fatigue as a possible predation defense.

Sick-building syndrome is an illness characterized by fatigue, headache, and upper-respiratory complaints. It is usually associated with modern office buildings, structures with an impervious outer shell and inoperable windows. Poor air quality, specific pollutants, and inadequate ventilation are considered common causes. The ability to smell faint odors requires air that is free of contamination. Human evolutionary ancestors depended on odors for survival. Even the slightest increase in the ability to smell a predator conveyed a distinct, immediate survival advantage. Conversely, an enormous survival advantage would also accrue to the animal that sought protection or avoided activity when this vital olfactory information was unavailable. Such would be the case with fire on the savannah. The foraging, olfactory dependent animal, unable to smell predators because of contaminated air, would be quickly snatched by a keen-sighted carnivore. There exist, however, well-described reflexes from the nose mediated through the trigeminal nerve that discourage activity when these free nerve endings are irritated. This mechanism may serve as a defense against predation. In adulterated atmosphere the animal, subdued by these reflexes, would be less likely to venture forth and, therefore, less vulnerable to predators. Similar reflexes may persist in humans, activated by poor air quality, air ill-suited for the dissemination of odors. I suggest that the human perception of these inhibitory reflexes is the feeling of fatigue associated with the sick building syndrome.

Air Pollution, Indoor↗
PubMed2004

Olfactory impairment in monozygotic twins discordant for schizophrenia.

OBJECTIVE: Several studies demonstrated olfactory dysfunction in patients with schizophrenia, some reported deficient olfaction in unaffected relatives of schizophrenics as well. This study differentially assessed olfactory acuity as well as smell identification and smell discrimination in monozygotic twins discordant for schizophrenia and healthy, monozygotic control twins, to determine the genetic basis of different olfactory modalities and their association to schizophrenia. METHOD: The Sniffin'Sticks test,a comprehensive and standardized olfactory test, was employed to assess the olfactory function of 10 monozygotic twin pairs discordant for schizophrenia versus 10 age- and sexmatched healthy,monozygotic twin pairs. RESULTS: Olfaction of affected monozygotic twins was globally impaired. Partial olfactory impairment of their unaffected co-twins may point to a genetic cause of olfactory impairment in schizophrenia. The influence of genetic factors was most evident for olfactory acuity and least evident for smell identification. All olfactory functions declined with duration of illness. Side of stimulus presentation did not influence olfactory performance. CONCLUSIONS: Genetic factors associated with olfactory dysfunction may contribute to schizophrenia. The degree of the genetic influence on olfaction depends on the olfactory domain under examination.

Adult↗
PubMed2006

Ethanol and methanol as possible odor cues for Egyptian fruit bats (Rousettus aegyptiacus).

Frugivorous bats from the Old and New World use odor cues to locate and assess fruit condition. We hypothesized that Egyptian fruit bats (Rousettus aegyptiacus) use as odor cues those volatile compounds that increase in emission rate as fruit ripens. We examined whether the smell of fermentation products may indicate the degree of ripeness to fruit bats. We analyzed volatile compounds in the headspace (the gas space above a fruit in a closed container) of dates (Phoenix dactylifera) and rusty figs (Ficus rubiginosa), both of which are consumed by fruit bats, to elucidate which compounds originate from fermentative pathways and to determine which change in emission rate during ripening. Ethanol, acetaldehyde, and acetic acid were the only volatile compounds detected as products of fermentation in both fruits. In dates, emission rates of these compounds increased during maturation, whereas in rusty figs, they decreased or remained constant. Methanol, although not a fermentation product, increased in emission rate during ripening in both fruits. We found that R. aegyptiacus was neither attracted nor deterred by the smell of methanol at any of the concentrations used. Although the odor of ethanol emanating from food containing concentrations similar to those found in ripe fruit did not attract the bats, at relatively high concentrations (> or =1%), the smell of ethanol deterred them. Thus, ethanol at high concentrations may serve as a signal for bats to avoid overripe, unpalatable fruit.

Animals↗
PubMed1992

The effect of odours on stimulated parotid salivary flow in humans.

We have previously shown that smell has no effect on resting parotid salivary flow in humans. In this study we investigated the effect of two odours on unilateral parotid salivary flow stimulated by either mastication or mastication with gustation. Neither odour stimulated flow above that elicited by either mastication or mastication with gustation. Removing an odour by sealing the nares has been reported to reduce stimulated parotid salivary flow, suggesting that smell contributes to stimulated salivary flow. However, in the present study, sealing the nares with a nose clip caused a significant reduction in the saliva elicited by an odourless stimulus. Even placing the nose clip over the bridge of the nose without sealing the nares significantly reduced the salivary flow, suggesting that the nose clip itself causes a reduction in stimulated parotid salivary flow. In conclusion, smell has no effect on stimulated parotid salivary flow in humans.

Adult↗
PubMed1993

Hyposmia in allergic rhinitis.

BACKGROUND: The association between nasal allergy and loss or diminution of smell is frequently alluded to in the literature; however, neither the true prevalence of hyposmia in individuals with allergic rhinitis nor its bases have been established. METHODS: We assessed olfactory threshold for phenylethyl alcohol in 91 patients with symptoms of allergic rhinitis and 80 nonatopic control subjects. To determine the degree to which nasal congestion contributes to hyposmia in allergic rhinitis, total nasal resistance was measured in 64 of the patients and 72 of the control subjects. RESULTS: Olfactory thresholds were significantly higher in allergic patients than in control subjects (p < 0.001), with 23.1% of the patients demonstrating a clinically significant smell loss (defined as threshold at or above the 2.5th percentile of control values). Although nasal resistance was significantly higher among patients than among controls (p < 0.001), it was not related to olfactory threshold in either group. Clinical or radiographic evidence of sinusitis or nasal polyps or both in allergy patients was found to be significantly associated with hyposmia (p < 0.006). CONCLUSIONS: The observed prevalence of hyposmia among patients with allergic rhinitis suggests that this is a major etiologic factor contributing to smell disorders. Sinusitis or nasal polyps or both may underlie many cases of allergy-related hyposmia.

Adolescent↗
PubMed1981

Olfactory bulb responsiveness to an aversive or novel food odor in ;the unrestrained rat.

The mechanisms subserving neophobia and learned aversion have been investigated by recording multiunit olfactory bulb discharges either in hungry rats following food deprivation or in satiated rats. Under the two conditions, rats were stimulated with the smell of their familiar maintenance diet or that of a novel food or of control food-unrelated odor. Responses to the odor of the novel food were tested, following a pairing of the first or the second intake of that food with a LiCl injection, or following its first intake paired with a NaCl control injection. All rats exhibited enhanced level of discharges when they were stimulated in the hungry state with the smell of the familiar food and not when stimulated with the non-alimentary control odor. The hunger to satiety modulation of olfactory bulb discharges, also exhibited in rats tested with the smell of the novel food, previously paired with NaCl, was absent after a LiCl-induced taste aversion to this odor. The small, although significant, modulation observed when the conditioning of aversion occurred with the less novel food is consistent with the view that learned safety prevails upon learned harmfulness. Results are discussed in terms of relations of olfactory bulb electrical responses to odors with food palatability, neophobia and learned aversion.

Animals↗
PubMed2006

Sensory deficits and olfactory system injury detected by novel application of MEMRI in newborn rabbit after antenatal hypoxia-ischemia.

Sensory deficits are frequently observed in cerebral palsy patients. The motor response to smell was found to be abnormal in an animal model of cerebral palsy following fetal hypoxia-ischemia. We hypothesized that fetal hypoxia-ischemia causes long-lasting and selective olfactory tract injury. A population of newborn rabbits with motor deficits was selected after spontaneous delivery following uterine ischemia at 22 days gestation (E22, 70% term). MnCl(2), 20 mg/kg, was administered in both nostrils at postnatal day 1 (E32). One nostril was occluded to control for smell augmentation through the other open nostril by intermittent amyl acetate stimulation for 6 h. T1-weighted MRI images were obtained on newborn rabbits. Amyl acetate exposure increased augmentation of Mn(2+) uptake in olfactory epithelium on the open side in control group but the augmentation was decreased after hypoxia. The proportion of animals with a greater enhancement in the open side increased in controls after amyl acetate, but not in hypoxia. Mn(2+) took longer to arrive at the olfactory bulbs and the rate of subsequent increase was slower in hypoxia. Concomitantly, the thickness of olfactory epithelium and the number of mature olfactory neurons, detected on olfactory marker protein immunostaining, were significantly less in the hypoxic group. Functional MRI studies are superior to neurobehavioral smell testing in the rabbit kits as they are more sensitive and quantifiable measures and do not depend upon the motor response. Antenatal hypoxia-ischemia causes long-lasting injury to neuronal tracts of the olfactory system including olfactory epithelium.

Animals↗
PubMedDate not supplied

Olfactory identification in elderly Greek people in relation to memory and attention measures.

The University of Pennsylvania Smell Identification Test (UPSIT) and the Cross-Cultural Smell Identification Test (CC-SIT) were administered to nondemented Greek participants ranging in age from 49 to 88 years together with tests of verbal memory from the Wechsler Memory Scale-3rd Edition (WMS-III). The test scores of the sample administered the CC-SIT were compared with the test scores of the 12 analogous UPSIT items of the sample administered the UPSIT. The percent of individuals correctly identifying each of the odorants of the UPSIT and CC-SIT is reported, together with means and standard deviations (S.D.) of the total smell scores. UPSIT performance in both the full test and the 12 analogous items was associated with WMS-III Logical Memory I performance after accounting for the effects of age, education and gender. CC-SIT performance was associated with gender, score on the Beck Depression Inventory-II and Logical Memory I performance. The study shows that olfactory identification is associated with verbal memory in nondemented individuals after accounting for demographic variables.

Aged↗
PubMed1999

Unilateral examination of olfactory threshold using the Jet Stream Olfactometer.

OBJECTIVE: The Jet Stream Olfactometer, a modification by the T&T olfactometer, has been recently developed and is now commercially available. This Jet Stream Olfactometer can routinely measure the unilateral sense of smell. Clinical usefulness of the Jet Stream Olfactometer was evaluated. METHODS: Twenty-three patients with sinus-related symptoms were examined. Unilateral olfactory acuity was examined using the Jet Stream Olfactometer and compared it with the anatomy of the olfactory cleft by computed tomographic (CT) scans. RESULTS: In 13 of the 23 patients examined the right olfactory threshold was similar to that of the left. Of these 13, in seven patients there was transport damage of the odorants and in the other six there was sensorineural damage. Ten patients showed an apparent difference between the right and left smell thresholds. Anosmia in seven of these ten patients was due to a conductive olfactory disturbance resulting from rhinosinusitis, whereas sensorineural damage was recognized in the other three patients. The difference in the detection threshold between the right and left nasal cavities was well correlated to that of the opacity between the right and left olfactory clefts. CONCLUSION: Jet Stream Olfactometer provides a convenient and reliable means for assessing the ability of unilateral smell.

Adult↗
PubMed2003

Taste-olfactory convergence, and the representation of the pleasantness of flavour, in the human brain.

The functional architecture of the central taste and olfactory systems in primates provides evidence that the convergence of taste and smell information onto single neurons is realized in the caudal orbitofrontal cortex (and immediately adjacent agranular insula). These higher-order association cortical areas thus support flavour processing. Much less is known, however, about homologous regions in the human cortex, or how taste-odour interactions, and thus flavour perception, are implemented in the human brain. We performed an event-related fMRI study to investigate where in the human brain these interactions between taste and odour stimuli (administered retronasally) may be realized. The brain regions that were activated by both taste and smell included parts of the caudal orbitofrontal cortex, amygdala, insular cortex and adjoining areas, and anterior cingulate cortex. It was shown that a small part of the anterior (putatively agranular) insula responds to unimodal taste and to unimodal olfactory stimuli, and that a part of the anterior frontal operculum is a unimodal taste area (putatively primary taste cortex) not activated by olfactory stimuli. Activations to combined olfactory and taste stimuli where there was little or no activation to either alone (providing positive evidence for interactions between the olfactory and taste inputs) were found in a lateral anterior part of the orbitofrontal cortex. Correlations with consonance ratings for the smell and taste combinations, and for their pleasantness, were found in a medial anterior part of the orbitofrontal cortex. These results provide evidence on the neural substrate for the convergence of taste and olfactory stimuli to produce flavour in humans, and where the pleasantness of flavour is represented in the human brain.

Brain↗
PubMed2000

The discrimination of dog odours by humans.

The domestic dog is able to identify both individual conspecifics, i.e. other dogs, and individual interspecifics, e.g. humans, by smell. Whilst humans can recognise individual members of their own species using olfactory information, it is unknown whether they can identify members of any other species in this manner. We examined the ability of humans to identify individual dogs by smell. Twenty-six dog owners were required to smell two blankets, one impregnated with the odour of their own dog, the other impregnated with the odour of an unfamiliar dog. Participants were required to indicate which of the odours smelt the strongest, which smelt the most pleasant, and which of the odours belonged to their own dog. Most of the participants (88.5%) were able to recognise the odour of their own dog. They showed no significant bias, however, in responding which of the odours they thought smelt the strongest or most pleasant. The results indicate that dogs produce odours that are individually distinctive to their owners, and highlight the fact that humans can recognise members of another species using olfactory cues--an ability presumably acquired without conscious effort.

Adult↗
PubMed2004

A controlled trial of aromatherapy for agitation in nursing home patients with dementia.

OBJECTIVES: Two controlled trials of aromatherapy to decrease agitation in persons with dementia have recently produced promising results. However, both studies combined the use of essential oils with massage. Thus, it is unclear if the effect of the aromatherapy intervention was the result of smelling or the cutaneous absorption of the oils. The purpose of this study was to determine whether smelling lavender oil decreases the frequency of agitated behaviors in patients with dementia. DESIGN: The study design was within-subjects ABCBA (A = lavender oil, B = thyme oil, C = unscented grapeseed oil): 4 weeks of baseline measurement, 2 weeks for each of the five treatment conditions (10-week total intervention time), and 2 weeks of postintervention measurement. Oil was placed every 3 hours on an absorbent fabric sachet pinned near the collarbone of each participant's shirt. SETTING: A long-term care facility specifically for persons with dementia. PARTICIPANTS: Seven agitated nursing home residents with advanced dementia. MEASUREMENTS: Agitation was assessed every 2 days using a modified Cohen-Mansfield Agitation Inventory. Olfactory functioning was assessed with structured olfactory identification and discrimination tasks, and with qualitative behavioral observation during those tasks. RESULTS: Split-middle analyses conducted separately for each patient revealed no treatment effects specific to lavender, no treatment effects nonspecific to pleasant smelling substances, and no treatment effects dependent on order of treatment administration. There were no differences between participants with more and less intact olfactory abilities. CONCLUSION: There is significant evidence in the neurologic and neuropsychologic literature that persons with dementia have impaired olfactory abilities. Concordant with this literature, this study found no support for the use of a purely olfactory form of aromatherapy to decrease agitation in severely demented patients. Cutaneous application of the essential oil may be necessary to achieve the effects reported in previous controlled studies.

Aged↗
PubMed1999

Odors: implicit memory and performance effects.

In order to assess the influence of odors on human performance and implicit memory for odors, 108 subjects completed a variety of tests in weakly scented (jasmine, lavender or odorless) rooms without having been made aware of the odor. After a 30 min interval the subjects were shown slides of different surroundings, including the room they had been in, and were requested to rate how well a set of 12 odors, including a blank, would fit to these surroundings. Half of these contexts contained visual cues related to two of the presented odors (leather and coffee). After the rating of fit the subjects had to rate the odors for pleasantness, were asked to identify the odors with their correct names and to tell where and when they had last smelled these odors. One subject remembered smelling the odor (jasmine) in the room and was discarded from the analysis of the results for the rating of fit. None of the others reported recollection of the experimental odors. The results showed that in general jasmine had a negative and lavender a positive effect on test performance. If an odor-related visual cue was present in the context, the related odor was always rated highest in fit to that context. Furthermore, the subjects working in rooms with an odor subsequently assigned this odor to the visual context of that room to a significantly higher degree than subjects working in rooms with different odors. Since none of the subjects reported that they had smelled the odor in the rooms where performance testing took place, it was concluded that the memory for these odors was implicit. Further analysis showed that such memory was only found in subjects who were unable to supply the right name for the odor. The possible consequences of this latter finding for understanding the relationship between sensory (episodic) and semantic odor memory are discussed.

Adult↗
PubMed2004

Effects of perceived and imagined odors on taste detection.

We assessed the influence of different odors on detection of a sweet tastant, and the ability of imagined odors to elicit the same effects as perceived odors on taste perception. The tastant used was sucrose, and the two odorants were strawberry and ham. In the first experiment, participants either smelled or imagined one of two odors during taste detection tasks (between-subject design), whereas in the second one, subjects completed both the odor imagery and perception conditions with taste detection tasks (within-subject design). The effect was odorant-specific: detection of sucrose was significantly better when subjects smelled strawberry than when they smelled ham. Furthermore, imagined odors influenced taste perception in the same way as did perceived odors. We concluded that the odor-specific effect on taste perception is an authentic perceptual phenomenon. Our results also support the notion that odor-induced changes in taste perception are mediated centrally. Finally, our findings are in agreement with reports supporting the existence of odor imagery.

Adolescent↗
PubMed2004

Odor-taste interactions: effects of attentional strategies during exposure.

Through repeated pairings with a tastant such as sucrose, odors are able to take on the tastant's qualities, e.g. by becoming more sweet smelling. When such odors are subsequently experienced with a sweet tastant in solution, the mixture is often given a higher sweetness rating than the tastant alone. Odor-induced taste enhancement appears to be sensitive to whether an odor-taste combination is viewed analytically as a set of discrete qualities, or synthetically as a flavor. The present research attempted to determine if adoption of these different perceptual approaches during co-exposure with sucrose would influence the extent to which an odor would become sweet smelling and subsequently enhance sweetness intensity. In Experiment 1, subjects received multiple exposures to mixtures of sucrose with low sweetness, low familiarity odors or, as a control, the odors and sucrose solutions separately. Two groups that received mixtures made intensity ratings that promoted either synthesis or analysis of the individual elements in the mixtures. The odors became sweeter smelling irrespective of group. Only adopting a synthetic strategy produced odors that enhanced sweetness in solution. However, these effects were also shown with a 'non-exposed' control odor. This could be accounted for if the single co-exposure with sucrose that all odors received in the pre-test was able to produce sweeter odors. A second experiment confirmed this prediction. Thus, while even a single co-exposure with sucrose is sufficient to produce a sweeter odor, the adoption of a synthetic perceptual strategy during the co-exposure is necessary to produce an odor that will enhance sweetness. These data are consistent with associative leaning accounts of how odors take on taste qualities and also support the interpretation that these effects reflect the central integration of odors and tastes into flavors.

Adolescent↗