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Results for “Olfactory Perception”

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PubMed2002

Odorant differentiated pattern of cerebral activation: comparison of acetone and vanillin.

Whether different odorous compounds (odorants) are processed by different cerebral circuits is presently unknown. A first step to address this complicated issue is to investigate how the cerebral regions mediating signals from olfactory (i.e., unimodal) odorants, differ from those mediating the olfactory + trigeminal (i.e., bimodal) odorants. [15O]-H2O-PET scans were conducted in 12 healthy females during three separate conditions: birhinal, passive smelling of: 1) the unimodal odorant vanillin; 2) the bimodal odorant acetone; and 3) odorless air. Significant activations were calculated contrasting vanillin to air, acetone to air, and deactivations, running these contrasts in the opposite direction. Smelling of vanillin activated bilaterally the amygdala and piriform cortex. These regions were only engaged slightly by acetone. Instead, strong activations were found in the anterior and central insula and claustrum, the posterior portion of anterior cingulate, the somatosensory cortex (SI for face), cerebellum, ventral medial (VMPo) and dorsal medial (MDvc) thalamus, the lateral hypothalamus, and pons/medulla. In parallel, the somatosensory (SI, below central representation of face), secondary visual and auditory cortices, as well as the supplementary motor area and the parahippocampal gyri were deactivated. No deactivations were observed with vanillin, although the odor components of acetone and vanillin were rated similarly intense (75 +/- 17 mm vs. 61 +/- 22 mm, NS). The differentiated pattern of cerebral activation during odorant perception seems to be dependent on the signal transducing cranial nerves involved. In contrast to vanillin, which solely activates the olfactory cortex, acetone engages predominantly trigeminal projections from the nasal mucosa. Acetone's limited activation of the olfactory cortex may result from a cross-modal interaction, with inhibition of acetone's odor component by its trigeminal component.

Acetone↗
PubMed1984

Social facilitation of muricidal behavior in the rat.

A phenomenon resembling social facilitation of muricide was described. Rats, who were already established mouse killers, killed mice faster in the presence of a large number of rats continuously killing mice. Evidence was presented which supports the argument that the facilitation was transmitted through auditory rather than olfactory cues.

Aggression↗
PubMed2005

Brain mechanisms for extracting spatial information from smell.

Forty years ago, von Békésy demonstrated that the spatial source of an odorant is determined by comparing input across nostrils, but it is unknown how this comparison is effected in the brain. To address this, we delivered odorants to the left or right of the nose, and contrasted olfactory left versus right localization with olfactory identification during brain imaging. We found nostril-specific responses in primary olfactory cortex that were predictive of the accuracy of left versus right localization, thus providing a neural substrate for the behavior described by von Békésy. Additionally, left versus right localization preferentially engaged a portion of the superior temporal gyrus previously implicated in visual and auditory localization, suggesting that localization information extracted from smell was then processed in a convergent brain system for spatial representation of multisensory inputs.

Adult↗
PubMed2003

Environmental odors and health hazards.

Using the recently developed and validated 'chemical diversity approach', the potential of chemicals, to be detected by the human olfactory system and to cause adverse health effects, was investigated. The analyses found no significant association between odor perceptibility and potential for inducing health effects.

Environmental Pollutants↗
PubMed1992

Memory in the chick: multiple cues, distinct brain locations.

Training chicks on a one-trial passive avoidance task results in memory-dependent synaptic remodeling in the intermediate medial hyperstriatum ventrale (IMHV) and lobus parolfactorius (LPO). Because pretraining IMHV lesions are amnestic and posttraining IMHV lesions are not, the functional significance of this remodeling requires explanation. Chicks use various cues to classify and remember objects. If the IMHV were concerned with memory for only one such cue, then posttraining IMHV lesions would not lead to "amnesia" because animals would still avoid the aversive bead using other contextual cues. This hypothesis was tested using a color discrimination task. IMHV lesions, but not LPO lesions, impair color discrimination, suggesting that the IMHV may be involved in classifying and remembering the bitter bead on the basis of color. Thus, even simple associations are stored in the brain in the form of multiple, dispersed representations.

Animals↗
PubMed1999

Odor structure-activity relationships compared in human and nonhuman primates.

The ability of 4 squirrel monkeys to distinguish between members of 3 homologous series of substances (aliphatic alcohols, aldehydes, and ketones) was investigated, and their performance was compared with that of a group of 10 human participants. With all 3 substance classes, and in both species, a significant negative correlation was found between discrimination performance and structural similarity of odorants in terms of differences in carbon chain length. These findings suggest carbon chain length of aliphatic odorants to be one of presumably several determinants of the interaction between stimulus molecule and olfactory receptor and support the assumption that human and nonhuman primates may share common mechanisms of odor quality perception.

Adult↗
PubMed1977

Evaluation of intranasal zinc sulfate treatment on olfactory discrimination in rats.

The effects of intranasal syringing with 5% zinc sulfate were assessed in rats trained in a wind-tunnel olfactometer to detect the presence of an odor or to discriminate odors of graded intensities. The syringing produced a severe but brief interference in olfactory performance. Full recovery of detection performance occurred within 72 hr after treatment. Initial recovery of odor intensity discrimination occurred in 2-8 days and full recovery within 8-10 days. These results suggest that intranasal syringing with ZnSO4 is not an adequate control for the effects of anosmia produced by olfactory bulbectomy.

Administration, Intranasal↗
PubMed1998

Who reads temporal information contained across synchronized and oscillatory spike trains?

Our inferences about brain mechanisms underlying perception rely on whether it is possible for the brain to 'reconstruct' a stimulus from the information contained in the spike trains from many neurons. How the brain actually accomplishes this reconstruction remains largely unknown. Oscillatory and synchronized activities in the brain of mammals have been correlated with distinct behavioural states or the execution of complex cognitive tasks and are proposed to participate in the 'binding' of individual features into more complex percepts. But if synchronization is indeed relevant, what senses it? In insects, oscillatory synchronized activity in the early olfactory system seems to be necessary for fine odour discrimination and enables the encoding of information about a stimulus in spike times relative to the oscillatory 'clock. Here we study the decoding of these coherent oscillatory signals. We identify a population of neurons downstream from the odour-activated, synchronized neuronal assemblies. These downstream neurons show odour responses whose specificity is degraded when their inputs are desynchronized. This degradation of selectivity consists of the appearance of responses to new odours and a loss of discrimination of spike trains evoked by different odours. Such loss of information is never observed in the upstream neurons whose activity is desynchronized. These results indicate that information encoded in time across ensembles of neurons converges onto single neurons downstream in the pathway.

Animals↗
PubMed1996

The nature and duration of adaptation following long-term odor exposure.

Any individual living or working in an odorous environment can experience changes in odor perception, some of which are long lasting. Often, these individuals report a significant reduction in the perception of an odor following long-term exposure to that odor (adaptation). Yet, most experimental analyses of olfactory adaptation use brief odorant exposures which may not typify real-world experiences. Using a procedure combining long-term odor exposure in a naturalistic setting with psychophysical tests in the laboratory, we present evidence to show that reduced odor intensity following long-term exposure is accompanied by odorant-specific shifts in threshold. Subjects were exposed continuously to one of two odorants while in their home for a period of 2 weeks. Exposure produced an odorant-specific reduction in sensitivity and perceived intensity compared with preexposure baselines: Detection thresholds for the adapting odorant were elevated following exposure and perceived intensity ratings for weak concentrations were reduced. For most individuals, reduced sensitivity to the test odorant was still evident up to 2 weeks following the last exposure. The persistence of the change, as evidenced by the duration of recovery from adaptation, distinguishes this phenomenon from the adaptation seen following shorter exposures and highlights the need for the study of exposure durations that are more similar to real-world exposures.

Adolescent↗
PubMedDate not supplied

[Pheromones: an underestimated communication signal in humans].

The pheromones are molecules, mainly aliphatic acids, with or without perceptible odor, recognized by specific receptors, the stimulation of which induces neuroendocrine reactions and affects the individual behavior. Olfactory receptors are underexpressed in human, 70 % of genes have become nonfunctional pseudogenes. But the remaining function was tested and is able to induce emotional reactions corresponding to a non-verbal signal of social interactions. In the present study, we review the actual knowledge on the olfactory receptors. They belong to the G-protein-coupled-receptors. Their signal is transduced to the hypothalamic-pituitary-gonadal axis. Some HLA-based olfactory cues are shown with reference to recent experiments. The pathophysiological hypotheses are considered with respect to studies in anorexia nervosa and Alzheimer' disease.

Animals↗
PubMed2004

Update on olfactory mucosal metabolic enzymes: age-related changes and N-acetyltransferase activities.

We have expanded previous observations on olfactory metabolic enzymes by examining the content of various metabolic enzymes in the olfactory mucosa of the male Long-Evans rat at different ages. Age-related changes in metabolic enzyme content may be related to changes in susceptibility to toxicants with age and may also contribute to altered odorant perception in the elderly. While some enzymes did not vary over the age range examined, decreases in the microsomal content of other enzymes were observed. While mRNA for acetyltransferase enzymes has previously been described in olfactory mucosa, the markedly higher activity of olfactory acetyltransferases compared to liver had not previously been described. Acetyltransferases are important in the metabolism of drugs and toxicants that are aromatic amine derivatives and may contribute to the bioactivation of rodent olfactory mucosal carcinogens such as 2,6-dimethylaniline and alachlor. These studies show that the olfactory mucosa varies in its metabolic capacity with age, and characterize another class of metabolic enzymes in the olfactory mucosa, both of which may impact significantly on responses to toxicants and therapeutic agents in the nasal cavity.

Acetyltransferases↗
PubMed2002

The correlation between physiological and psychological responses to odour stimulation in human subjects.

OBJECTIVES: To correlate physiological and psychological responses to odour stimulation. METHODS: Olfactory event-related potentials (OERP) were recorded from human subjects in response to different odour pulse protocols. Pulse duration and interstimulus interval (ISI) were varied while the subjects recorded pulse detection by a button press. RESULTS: There was a correlation between odour strength and OERP. The amplitude of the OERP (peak positive-peak negative) declined by 48% with repetitive stimulation for all stimulus strengths. The time constant for this decline (adaptation) was concentration dependent and varied from 10 to 4 s for increasing odorant strength (from 35 to 200 ms pulse of saturated amyl acetate vapour diluted 1:3 at 3 l min(-1) at 24 degrees C). The psychometric test score (cognitive odour perception) was also concentration dependent and increased with increasing stimulus strength at all ISIs except the lowest value; 2.5 s. At this ISI adaptation/habituation interfered with the dose-response. The decline of the psychometric test score with increasing stimulus frequency (decreasing ISI) was more rapid (tau approximately 2.5 s) than that of the OERP. The psychometric test score declined to zero at a constant rate and was not dependent upon stimulus strength. CONCLUSIONS: Continuous olfactory stimulation results in a shut-down of cognitive perception with a time constant of around 2.5 s while the response of the physiological system (receptors, transduction and relay system) declines by about 50% with a slower time course (> or = 4 s). This former process defines habituation in the olfactory system while the latter describes adaptation. Since the adaptation process is concentration dependent the rate of adaptation contains information about odour strength, thus both the amplitude of the OERP and the rate of adaptation could encode stimulus strength.

Adaptation, Physiological↗
PubMed1998

Human olfactory bulb: aging of glomeruli and mitral cells and a search for the accessory olfactory bulb.

The aims of this study on the human olfactory bulb were two. First morphometry of the bulbs revealed marked declines during aging in the numbers of mitral cells and glomeruli, the bulb's principal integrative and relay elements. Numbers of glomeruli and mitral cells in each bulb of the young adult human were found to be approximately 8,000 and 40,000, respectively; these numbers declined steadily with age at an approximate rate of 10% per decade, so that in the ninth and tenth decades less than 30% of these elements remain in place. Such a marked decline with aging is suggested to underlie in part the decline in olfactory abilities (odor detection and identification) of humans with aging. In a separate study a systematic search for presence of an accessory olfactory bulb in the adult and aging bulbs was undertaken. No positive evidence for such an organized formation was found in the various regions of the adult bulbs of different age groups. The implications of these negative findings for the recent theories on human vomeronasal function and pheromonal perception are discussed.

Adult↗
PubMed2004

Experience-dependent neural integration of taste and smell in the human brain.

Flavor perception arises from the central integration of peripherally distinct sensory inputs (taste, smell, texture, temperature, sight, and even sound of foods). The results from psychophysical and neuroimaging studies in humans are converging with electrophysiological findings in animals and a picture of the neural correlates of flavor processing is beginning to emerge. Here we used event-related fMRI to evaluate brain response during perception of flavors (i.e., taste/odor liquid mixtures not differing in temperature or texture) compared with the sum of the independent presentation of their constituents (taste and/or odor). All stimuli were presented in liquid form so that olfactory stimulation was by the retronasal route. Mode of olfactory delivery is important because neural suppression has been observed in chemosensory regions during congruent taste-odor pairs when the odors are delivered by the orthonasal route and require subjects to sniff. There were 2 flavors. One contained a familiar/congruent taste-odor pair (vanilla/sweet) and the other an unfamiliar/incongruent taste-odor pair (vanilla/salty). Three unimodal stimuli, including 2 tastes (sweet and salty) and one odor (vanilla), as well as a tasteless/odorless liquid (baseline) were presented. Superadditive responses during the perception of the congruent flavor compared with the sum of its constituents were observed in the anterior cingulate cortex (ACC), dorsal insula, anterior ventral insula extending into the caudal orbitofrontal cortex (OFC), frontal operculum, ventral lateral prefrontal cortex, and posterior parietal cortex. These regions were not present in a similar analysis of the incongruent flavor compared with the sum of its constituents. All of these regions except the ventrolateral prefrontal cortex were also isolated in a direct contrast of congruent - incongruent. Additionally, the anterior cingulate, posterior parietal cortex, frontal operculum, and ventral insula/caudal OFC were also more active in vanilla + salty minus incongruent, suggesting that delivery of an unfamiliar taste-odor combination may lead to suppressed neural responses. Taken together with previous findings in the literature, these results suggest that the insula, OFC, and ACC are key components of the network underlying flavor perception and that taste-smell integration within these and other regions is dependent on 1) mode of olfactory delivery and 2) previous experience with taste/smell combinations.

Adult↗
PubMed1993

Nutrition and chemosensory perception in the elderly.

The elderly person's perception of foods and food flavor is affected by age-associated changes in the chemical senses (taste, smell, and trigeminal sensation). Both classic and modern psychophysical techniques have been applied to achieve some understanding of these changes. Taste threshold sensitivity declines with age; however, the magnitude of the decline and the degree to which taste qualities are differentially affected remains to be understood. Suprathreshold taste intensity perception is affected by age, but there is a differential effect of taste quality. Experiments with blended foods have indicated that both olfactory and taste deficits contribute to older people's difficulty with food identification. Experiments assessing threshold sensitivity, suprathreshold intensity, and suprathreshold identification have all demonstrated significant impairment in olfaction in old age. In fact, these effects are far greater than in the taste system. Patients with Alzheimer's disease show even greater olfactory deficits than normal elderly and the effect is related to the degree of dementia. We have ruled out nasal disease in these patients as the primary causes of olfactory insensitivity, because significant impairment remains when the influence of nasal airflow and nasal cytology has been removed statistically. Both normal elderly and patients with Alzheimer's disease show impairment in odor memory. Sensitivity to, familiarity with, and identifiability of the odors all play a role in odor memory performance. Flavor preference also changes over the lifespan. Older subjects, for instance, rate high concentration of sugar and salt as pleasanter than young subjects do. Multiple influences contribute to this phenomenon. Elderly persons and those of lower nutritional status have shown preferences for higher concentrations of casein hydrolysate than young persons and those of higher nutritional status, suggesting that dietary preference can be related to chemosensory cues. There are significant age-associated changes in chemosensory perception that have the potential to interact with dietary selection and nutrition in the elderly. A better understanding of these phenomena may promote health and well-being in the elderly.

Aged↗
PubMed1999

The smell map: is there a commonality of odour perception?

The normal perception of odour quality is poorly understood, so formulating meaningful tests of olfaction is difficult. While tests of odour discrimination and odour detection threshold have helped quantify olfactory dysfunction, there are not yet predictive relationships between sensitivity to particular odours and particular forms of olfactory dysfunction. Using 11 commonly encountered odours, 20 normosmics performed similarity ratings of odour pairs. Multidimensional scaling, a standard behavioural sciences data analysis method, was used to explore the perceptual relationships between the odours based on their pair-wise similarity ratings. Smell maps were created for each individual as was a common or archetypal map which indicated a commonality in individuals' odour perception, far greater than chance alone (P < 10(-6)). A preliminary analysis of four hyposmics suggests that they do not conform to the normosmic archetype. Future studies assessing the relationship between odours in the archetype should improve the selection of odours to be included in tests of odour discrimination.

Adult↗
PubMed1997

Central processing of odor concentration is a temporal phenomenon as revealed by chemosensory event-related potentials (CSERP).

Chemosensory event-related potentials (CSERP) can be used to examine central nervous odor processing. An important question for understanding odor perception is how different concentrations are processed. In the present study two odors were chosen which activate either the olfactory (linalool) or the trigeminal (menthol) system. Both odors were presented to 11 subjects in four different concentrations. Four subjects had to attend actively to the odors while the others perceived the odors under passive attention. The results showed that increased concentrations of the olfactory stimulus resulted in shorter latencies of the N1 component but did not affect the amplitudes of the CSERP. However, the amplitudes of the stimulus dependent, exogenous components (N1, P2) increased with higher concentrations of the trigeminal stimulus. The amplitude of the late positive complex, which reflects endogenous processes, was usually larger when the odorous stimuli had to be attended to actively. It is concluded that olfactory intensity coding results in a qualitatively different but not in a stronger neuronal response of the human brain.

Adult↗