Olfactory metacognition

The current paper focuses on the subjective knowledge people have about their ability to name odors. Previous investigations of such metacognitive aspects of olfactory cognition are very scarce and have yielded results that need further scrutiny. In two experiments, we investigated three metamemory judgments about odor identity. As opposed to previous findings, participants' feeling of knowing judgments about odor identity predicted later recognition. Participants were also accurate but highly overconfident in their retrospective confidence in odor identification. A strong and imminent feeling of being able to name an odor, a so-called 'tip of the nose' experience, was found to predict later recall, but was otherwise poorly related to any partial activation of the odor name or other information associated with the odor. This makes it different from the commonly investigated 'tip of the tongue' phenomenon. The current study shows that olfactory metamemory is related to actual knowledge, a finding that is in line with what has been observed for other modalities.     

Judgement of odor intensity is influenced by subjects' knowledge of the odor source

Odor perception, including intensity, is affected by knowledge of odor source. For 76 subjects tested with 24 everyday odorants, ratings of intensity, pleasantness and familiarity were enhanced when subjects either could identify the odor source themselves or were provided with the name by the experimenter. Ratings were highest when subjects judged that the names provided matched their own perception, suggesting an interaction between individuals' cognitive representation of odors and their immediate perceptual experience.     

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.     

Body odor similarity in noncohabiting twins

There is currently considerable interest in biometric approaches using human odor as a marker of disease or genetic individuality. Body odor is also thought to be used during mate choice to select genetically compatible mates. The idea that body odor reveals information about both genetic identity and genetic similarity is most readily tested by examining odor in twin pairs. However, although this idea can be traced back 130 years to Francis Galton in 1875, most studies using dogs fail to control for shared environmental effects associated with cohabitation. Here we show that odors of identical twins (but not dizygotic twins) can be matched by human sniffers at rates better than chance, even when the twins are living apart. In addition, matching frequencies for identical twin odors were not significantly different from those for duplicate odors from the same individual. These results indicate an important genetic influence on body odor and the potential for developing technologies for human odor printing in relation to underlying genotype.     

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.     

Slow breathing and emotions associated with odor-induced autobiographical memories

An important feature of olfactory perception is its dependence on respiratory activity. By inspiration, olfactory information ascends directly to olfactory-related limbic structures. Therefore, every breath with odor molecules activates these limbic areas associated with emotional experience and memory retrieval. We tested whether odors associated with autobiographical memories can trigger pleasant emotional experiences and whether respiration changes during stimulation with these odors. During presentation of odors related to autobiographical memories and control odors, we measured minute ventilation, tidal volume, respiratory frequency, O2 consumption, and end tidal CO2 concentration. Findings showed that autobiographical memory retrieval was associated with increasing tidal volume and decreasing respiratory frequency more than during presentation of control odors. Subjective feelings such as emotional arousal during retrieval of the memory, arousal level of the memory itself, or pleasantness and familiarity toward the odor evoked by autobiographical memory were more specific emotional responses compared with those related to control odors. In addition, high trait anxiety subjects responded with a stronger feeling of being taken back in time and had high arousal levels with tidal volume increases. We discussed assumptions regarding how deep and slow breathing is related to pleasantness and comfortableness of an autobiographical memory.     

Odor naming methodology: correct identification with multiple-choice versus repeatable identification in a free task

Since there is rarely a social labeling consensus in the identification of odors, it would be better to assess whether participants identify an odor by the same name upon repeated presentation rather than by the name designated as 'correct' by the experimenter (veridical label) in identification tasks. To examine the relevance of this proposition, participants were asked to identify familiar odors both in a free and a multiple-choice task. The free task was replicated in order to determine the percentage of repeatable identification. Results showed that the difference between the percentage of correct identification in the multiple-choice task and the percentage of repeatable identification in the free task was small, and that participants often used a repeatable name which differed from the veridical label. Thus, it was suggested that allowing participants to give their own name to an odor when it is not present on a pre-developed list, and measuring whether participants repeat the same name in independent measurements, might improve the relevance of multiple-choice tasks.     

Testing for Odor Discrimination and Habituation in Mice

This video demonstrates a technique to establish the presence of a normally functioning olfactory system in a mouse. The test helps determine whether the mouse can discriminate between non-social odors and social odors, whether the mouse habituates to a repeatedly presented odor, and whether the mouse demonstrates dishabituation when presented with a novel odor. Since many social behavior tests measure the experimental animal’s response to a familiar or novel mouse, false positives can be avoided by establishing that the animals can detect and discriminate between social odors. There are similar considerations in learning tests such as fear conditioning that use odor to create a novel environment or olfactory cues as an associative stimulus. Deficits in the olfactory system would impair the ability to distinguish between contexts and to form an association with an olfactory cue during fear conditioning. In the odor habitation/dishabituation test, the mouse is repeatedly presented with several odors. Each odor is presented three times for two minutes. The investigator records the sniffing time directed towards the odor as the measurement of olfactory responsiveness. A typical mouse shows a decrease in response to the odor over repeated presentations (habituation). The experimenter then presents a novel odor that elicits increased sniffing towards the new odor (dishabituation). After repeated presentation of the novel odor the animal again shows habituation. This protocol involves the presentation of water, two or more non-social odors, and two social odors. In addition to reducing experimental confounds, this test can provide information on the function of the olfactory systems of new knockout, knock-in, and conditional knockout mouse lines.     

Brief Exposure to Female Odors “Emboldens” Male Mice by Reducing Predator-Induced Behavioral and Hormonal Responses

In rodents, where chemical signals play a particularly important role in determining intersexual interactions, various studies have shown that male behavior and physiology is sensitive to female odor cues. Here we examined the effects of brief (1 min) and more prolonged (60 min) preexposure to the odors of a novel estrous female on the behavioral and hormonal responses of sexually experienced and inexperienced male mice, Mus musculus, to subsequent predator (cat and weasel) odor exposure and potential predator risk. Brief, but not prolonged, preexposure to the odors of an estrous female decreased the aversion and avoidance responses of male mice to cat odor in a Y-maze preference test, with the extent of responses being affected by a males prior sexual experience. Similarly, brief, but not prolonged, preexposure to female odors markedly attenuated the analgesic responses elicited in male mice by weasel odor. Brief exposure to a novel estrous female by itself had no significant immediate effects on either corticosterone or testosterone levels in the males. However, brief, but not prolonged, preexposure to the odors of an estrous female attenuated the marked increase in corticosterone and decrease in testosterone that were induced in males by exposure to weasel odor. The decreases in aversive responses to, and effects of, predator odor exposure that are induced by brief exposure to a novel estrous female may reflect a greater risk taking and boldness in males that could directly facilitate access to an immediately, and possibly transiently, available novel sexually receptive female.     

Information use by an Invading Species: Do Invaders Respond More to Alarm Odors than Native Species?

Two species of crayfish were tested in the laboratory to evaluate the hypothesis that successful invaders use a broader range of chemical information than do displaced native species. The invasive species Orconectes rusticus reduced responses to food odors just as strongly when heterospecific (O. propinquus, O. virilis) alarm odors were introduced with food odors as they did when conspecific alarm odors were introduced at the same time as food odors. Individuals of the displaced native species, O. propinquus, did not reduce feeding responses as strongly when O. virilis alarm odor was introduced as with conspecific alarm odor or O. rusticus alarm odor. These results are consistent with the hypothesis that successful invaders use a wider range of information about their environment than do displaced native species.     

The Emotional Distinctiveness of Odor-evoked Memories

A modified paired-associate learning paradigm was used to testwhether odors or verbal odor labels evoked more emotional memories.Subjects were presented with emotionally positive and negativepaintings (to-be-remembered items) in association with positiveand negative odors and odor labels. Painting recall and associatedemotional experience were tested after 48 h. Odor-evoked memorieswere found to be more emotional than verbally cued memorieson a variety of measures. Moreover, if the cue for recall (odoror label) was hedonically congruent with the painting to beremembered, memory for original emotional experiences was enhanced.The findings are discussed within a general cognitive frameworkand implications for using odors to dissociate the emotionaland representational aspects of memory are addressed. Chem.Senses 20: 517–528, 1995.     

Population level evidence for seasonality of the human microbiome

The objective of this study is to determine whether human body odors undergo seasonal modulation. We utilized google trends search volume from the United States of America from January 1, 2010 to June 24, 2017 for a number of predetermined body odors. Regression modeling of time series data was completed. Our primary outcome was to determine the proportion of the variability in Internet searches for each unpleasant odor (about the mean) that is explained by a seasonal model. We determined that the seasonal (sinusoidal) model provided a significantly better fit than the null model (best straight line fit) for all searches relating to human body odors (P <.0001 for each). This effect was easily visible to the naked eye in the raw time series data. Seasonality explained 88% of the variability in search volume for flatulence (i.e. R2 = 0.88), 65% of the variability in search volume for axillary odor, 60% of the variability in search volume for foot odor, and 58% of the variability in search volume for bad breath. Flatulence and bad breath tended to peak in January, foot odor in February, and Axillary odor in July. We conclude that searching by the general public for information on unpleasant body odors undergoes substantial seasonal variation, with the timing of peaks and troughs varying with the body part involved. The symptom burden of such smells may have a similar seasonal variation, as might the composition of the commensal bacterial microflora that play a role in creating them     

Impaired discrimination of and aversion to parasitized male odors by female oxytocin knockout mice

A major cost of social behavior is the increased risk of exposure to parasites, with animals utilizing social information to recognize and avoid infected conspecifics. In mice, females can discriminate between infected and uninfected males on the basis of social cues, displaying aversive responses to the odors of infected males. In the present study, using female mice whose gene for oxytocin (OT) has been selectively deleted (OT knockout mice (OTKO)), we show that at least one normal allele for OT is required for the mediation of the recognition and avoidance of parasitized males. Female wild type (OTWT) and heterozygous (OTHZ) mice distinguished between the odors of individual males infected with the louse, Polyplax serrata , and uninfected males while the KO mice did not. Exposure to the odors of infected males induced analgesia in OTWT and OTHZ females, with OTKO females displaying attenuated analgesia. OTWT and OTHZ females, but not the OTKO females, also distinguished between the odors of novel and familiar infected males and modulated their analgesic responses on the basis of prior familiarity. In an odor choice test, OTWT and OTHZ females displayed a marked initial choice for the odors of uninfected males, whereas the OTKO females showed no consistent choice. This impairment was specific to the odors of infected males. OTKO females displayed normal analgesic responses to another aversive social odor, that of a stressed male, and an aversive non-social odor, that of a cat. The OTKOs had normal non-social olfactory memory, but were impaired in their social odor memory. These findings indicate that a normal OT gene comprises an essential part of the central recognition mechanism whereby females can both reduce the transmission of parasites to themselves and select for parasite-free males.     

Color enhances orthonasal olfactory intensity and reduces retronasal olfactory intensity

The effect of color on orthonasal and retronasal odor intensities was investigated. When odorants were smelled orthonasally (i.e., through the nostrils), color enhanced odor intensity ratings, consistent with previous reports. However, when odorants were smelled retronasally (i.e., the odorous solution was put in the mouth), color reduced odor intensity ratings. These different effects of color on odor intensity (i.e., enhancement orthonasally and suppression retronasally) appear to be the result of route of olfactory stimulation rather than of any procedural artifact. This supports previous reports that retronasal and orthonasal odors are perceived differently.     

Olfactory Associative Learning of the Pupal Parasitoid Pimpla luctuosa Smith (Hymenoptera: Ichneumonidae)

Laboratory experiments were conducted to determine the role of learning in olfactory host searching by the ichneumonid pupal parasitoid, Pimpla luctuosa Smith. Females learned to associate novel odors such as vanilla and strawberry with hosts when they oviposited in at least several hosts with the odors. Repeated experiences of hosts with an odor increased the response of the experienced odor, and females that had experienced host odor seven times responded to the experienced odors 90% of the time. Although the response by females to a learned odor gradually decreased with increasing host-deprivation time, 60% of the females that had experienced host odor 7 days earlier still responded to the experienced odor. Females also learned two separate odors associated with hosts at a time and responded to both odors without a preference for one odor over the other. When trained two separate odors with hosts, females learned the second odor more quickly than the first odor. After females experienced several stings in simulated hosts with the previously learned odor, they ceased to respond to the learned odor, suggesting that repeated unrewarding experiences cause females to cease to respond to the learned odors.     

“Did You Call Me?” 5-Month-Old Infants Own Name Guides Their Attention

An infant's own name is a unique social cue. Infants are sensitive to their own name by 4 months of age, but whether they use their names as a social cue is unknown. Electroencephalogram (EEG) was measured as infants heard their own name or stranger's names and while looking at novel objects. Event related brain potentials (ERPs) in response to names revealed that infants differentiate their own name from stranger names from the first phoneme. The amplitude of the ERPs to objects indicated that infants attended more to objects after hearing their own names compared to another name. Thus, by 5 months of age infants not only detect their name, but also use it as a social cue to guide their attention to events and objects in the world.     

Odor similarity does not influence the time needed for odor processing

The brain's link between perception and action involves several steps, which include stimulus transduction, neuronal coding of the stimulus, comparison to a memory template and choice of an appropriate behavioral response. All of these need time, and many studies report that the time needed to compare two stimuli correlates inversely with the perceived distance between them. We developed a behavioral assay in which we tested the time that a honeybee needs to discriminate between odors consisting of mixtures of two components, and included both very similar and very different stimuli spanning four log-concentration ranges. Bees learned to discriminate all odors, including very similar odors and the same odor at different concentrations. Even though discriminating two very similar odors appears to be a more difficult task than discriminating two very distinct substances, we found that the time needed to make a choice for or against an odor was independent of odor similarity. Our data suggest that, irrespective of the nature of the olfactory code, the bee olfactory system evaluates odor quality after a constant interval. This may ensure that odors are only assessed after the olfactory network has optimized its representation.     

On the tip of the tongue: an event-related fMRI study of semantic retrieval failure and cognitive conflict.

The tip of the tongue (TOT) state refers to a temporary inaccessibility of information that one is sure exists in long-term memory and is on the verge of recovering. Using event-related fMRI, we assessed the neural correlates of this semantic retrieval failure to determine whether the anterior cingulate-lateral prefrontal neural circuit posited to mediate conflict resolution is engaged during metacognitive conflicts that arise during the TOT. Results revealed that, relative to successful retrieval or unsuccessful retrieval not accompanied by a TOT, retrieval failures accompanied by TOTs elicited a selective response in anterior cingulate-prefrontal cortices. During a TOT, cognitive control mechanisms may be recruited in attempts to resolve the conflict and retrieval failure that characterize this state.     

"What-Where-Which" Episodic Retrieval Requires Conscious Recollection and Is Promoted by Semantic Knowledge

Episodic memory is defined as the conscious retrieval of specific past events. Whether accurate episodic retrieval requires a recollective experience or if a feeling of knowing is sufficient remains unresolved. We recently devised an ecological approach to investigate the controlled cued-retrieval of episodes composed of unnamable odors (What) located spatially (Where) within a visual context (Which context). By combining the Remember/Know procedure with our laboratory-ecological approach in an original way, the present study demonstrated that the accurate odor-evoked retrieval of complex and multimodal episodes overwhelmingly required conscious recollection. A feeling of knowing, even when associated with a high level of confidence, was not sufficient to generate accurate episodic retrieval. Interestingly, we demonstrated that the recollection of accurate episodic memories was promoted by odor retrieval-cue familiarity and describability. In conclusion, our study suggested that semantic knowledge about retrieval-cues increased the recollection which is the state of awareness required for the accurate retrieval of complex episodic memories.     

Body odor evoked potentials: a new method to study the chemosensory perception of self and non‐self in humans

A new method will be presented which allows the perception of body odors in humans to be studied objectively. The analysis of body odor‐evoked potentials was used to investigate if and how the human brain is able to differentiate self from non‐self body odor for the first time. Six subjects (three females) participated in two experimental sessions. In each session, two body odors (axillary hair) were presented within an olfactory oddball paradigm. One of the odors was collected from the subject and the other from an odor donor of the same sex. In the first session the subjects' attention was distracted to a secondary task (passive paradigm), in the second session the subjects were asked to actively differentiate the odors (active paradigm). For the EEG recordings the odors were presented within a constantly flowing airstream. The results show that the subjects could hardly differentiate the body odors subjectively. However, it could be demonstrated that the central nervous processing of one's own odor was faster than the processing of the chemosensory non‐self signal. Moreover, in the active paradigm, the potentials appeared to be larger when the subjects perceived their own body odor. The conclusion is reached that the measurement of chemosensory event‐related potentials (CSERP) is the method of choice for the investigation of HLA‐associated body odors. This revised version was published online in July 2006 with corrections to the Cover Date.