On the similarity of odor and language perception

Augmenting insect olfaction performance through nano-neuromodulation

Biological olfactory systems are highly sensitive and selective, often outperforming engineered chemical sensors in highly complex and dynamic environments. As a result, there is much interest in using biological systems to build sensors. However, approaches to read-out information from biological systems, especially neural signals, tend to be suboptimal due to the number of electrodes that can be used and where these can be placed. Here we aim to overcome this suboptimality in neural information read-out by using a nano-enabled neuromodulation strategy to augment insect olfaction-based chemical sensors. By harnessing the photothermal properties of nanostructures and releasing a select neuromodulator on demand, we show that the odour-evoked response from the interrogated regions of the insect olfactory system can not only be enhanced but can also improve odour identification.

Functional brain network properties of healthy full-term newborns quantified by scalp and source-reconstructed EEG

OBJECTIVE

Identifying the functional brain network properties of term low-risk newborns using high-density EEG (HD-EEG) and comparing these properties with those of established functional magnetic resonance image (fMRI) - based networks.

METHODS

HD-EEG was collected from 113 low-risk term newborns before delivery hospital discharge and within 72 hours of birth. Functional brain networks were reconstructed using coherence at the scalp and source levels in delta, theta, alpha, beta, and gamma frequency bands. These networks were characterized for the global and local network architecture.

RESULTS

Source-level networks in all the frequency bands identified the presence of the efficient small world (small-world propensity (SWP) > 0.6) architecture with four distinct modules linked by hub regions and rich-club (coefficient > 1) topology. The modular regions included primary, association, limbic, paralimbic, and subcortical regions, which have been demonstrated in fMRI studies. In contrast, scalp-level networks did not display consistent small world architecture (SWP < 0.6), and also identified only 2-3 modules in each frequency band.The modular regions of the scalp-network primarily included frontal and occipital regions.

CONCLUSIONS

Our findings show that EEG sources in low-risk newborns corroborate fMRI-based connectivity results.

SIGNIFICANCE

EEG source analysis characterizes functional connectivity at the bedside of low-risk newborn infants soon after birth.

Non-food odors and the duality of smell: Impact of odorant delivery pathway and labeling convention on olfactory perception

The olfactory system encompasses two perceptual pathways (orthonasal and retronasal) that activate the same receptors in the olfactory epithelium yet are thought to elicit different perceptions. Presently, a novel matching paradigm was employed using a non-food flavor set with low retronasal familiarity (honeysuckle, lavender, rose, and jasmine) to evaluate the effect of odor type on the Duality of Smell. Additionally, the influence of cognitive strategies used by subjects was assessed by manipulating the naming convention seen by the subjects: familiar (Honeysuckle, Lavender, Rose, Jasmine), unfamiliar (Inodora, Pedunculata, Beggeriana, Didymum), and generic (A, B, C, D). Subjects were presented with a reference, either in a vial (orthonasal delivery, ON) or a 2 oz. cup (retronasal delivery, RN) and instructed to match the same aroma from four unknowns, evaluated either by the same delivery route (congruent, e.g., ON-ON, RN-RN) or different route (incongruent, e.g., ON-RN, RN-ON) than the reference evaluation. All possible combinations of orthonasal and retronasal delivery for the reference and unknowns (e.g. ON-ON, RN-RN, ON-RN, RN-ON) were assessed by all subjects. Matching performance and signal detection measures indicated that, on average, subjects performed significantly better in the congruent conditions than in the incongruent conditions. These results suggest perceptual quality of aromas is route dependent and extend the Duality of Smell hypothesis to samples with low retronasal familiarity such as non-food odors. Labeling convention also had an impact on performance but, surprisingly, not in the direction anticipated. Indeed, as the information contained in the label decreased from familiar to generic reference names, performance increased. Moreover, depending on the labeling convention used, certain aromas were easier to match than others. The present research suggests odorant matching is a function of stimulus quality, cognitive strategy, and labeling convention.

Duality of Smell: Route-Dependent Effects on Olfactory Perception and Language

Olfactory research in humans has largely focused on odors perceived via sniffing, orthonasal olfaction, whereas odors perceived from the mouth, retronasal olfaction, are less well understood. Prior work on retronasally presented odors involves animal models and focus mainly on odor sensitivity, but little is known about retronasal olfactory perception and cognition in humans. In this study, we compared orthonasal and retronasal odor presentation routes to investigate differences in odor descriptions and evaluations. Thirty-six individuals participated in a within-subjects study using twelve odors (varying in pleasantness and edibility) in perceptual and semantic tasks. Orthonasal presentation was associated with a better ability to identify odors, and with more concrete (and source-based) language. Exploratory analyses revealed that whereas orthonasal odors were described with words that had visual associations, retronasal odors were described with words that had interoceptive associations. Interestingly, these route-dependent differences in descriptor usage were not explained by differences in sensitivity and intensity, suggesting instead a cognitive and linguistic processing difference between odors presented orthonasally and retronasally. Our results indicate that olfaction is, in fact, a dual sense, in which the routes change the perception of an odor.

Human Olfaction at the Intersection of Language, Culture, and Biology

The human sense of smell can accomplish astonishing feats, yet there remains a prevailing belief that olfactory language is deficient. Numerous studies with English speakers support this view: there are few terms for odors, odor talk is infrequent, and naming odors is difficult. However, this is not true across the world. Many languages have sizeable smell lexicons - smell is even grammaticalized. In addition, for some cultures smell talk is more frequent and odor naming easier. This linguistic variation is as yet unexplained but could be the result of ecological, cultural, or genetic factors or a combination thereof. Different ways of talking about smells may shape aspects of olfactory cognition too. Critically, this variation sheds new light on this important sensory modality.

Limitations in odour simulation may originate from differential sensory embodiment

Across diverse lineages, animals communicate using chemosignals, but only humans communicate about chemical signals. Many studies have observed that compared with other sensory modalities, communication about smells is relatively rare and not always reliable. Recent cross-cultural studies, on the other hand, suggest some communities are more olfactorily oriented than previously supposed. Nevertheless, across the globe a general trend emerges where olfactory communication is relatively hard. We suggest here that this is in part because olfactory representations are different in kind: they have a low degree of embodiment, and are not easily expressed as primitives, thereby limiting the mental manipulations that can be performed with them. New exploratory data from Dutch children (9-12 year-olds) and adults support that mental imagery from olfaction is weak in comparison with vision and audition, and critically this is not affected by language development. Specifically, while visual and auditory imagery becomes more vivid with age, olfactory imagery shows no such development. This is consistent with the idea that olfactory representations are different in kind from representations from the other senses. This article is part of the Theo Murphy meeting issue 'Olfactory communication in humans'.

Impaired Odor Perception in Autism Spectrum Disorder Is Associated with Decreased Activity in Olfactory Cortex

Autism Spectrum Disorders (ASDs) are characterized by atypical sensory functioning in the visual, tactile, and auditory systems. Although less explored, olfactory changes have been reported in ASD patients. To explore these changes on a neural level, 18 adults with ASD and 18 healthy neurotypical controls were examined in a 2-phase study. Participants were first tested for odor threshold and odor identification. Then, (i) structural magnetic resonance (MR) images of the olfactory bulb were acquired, and (ii) a functional MR imaging olfaction study was conducted. ASD patients exhibited decreased function for odor thresholds and odor identification; this was accompanied by a relatively decreased activation in the piriform cortex. In conclusion, these findings suggest, that the known alterations in olfaction in ASD are rooted in the primary olfactory cortex.

Sex Differences in Human Olfaction: A Meta-Analysis

Although the view that women's olfactory abilities outperform men's is taken for granted, some studies involving large samples suggested that male and female olfactory abilities are actually similar. To address this discrepancy, we conducted a meta-analysis of existing studies on olfaction, targeting possible sex differences. The analyzed sample comprised n = 8 848 (5 065 women and 3 783 men) for olfactory threshold (as measured with the Sniffin Sticks Test; SST), n = 8 067 (4 496 women and 3 571 men) for discrimination (SST), n = 13 670 (7 501 women and 6 169 men) for identification (SST), and a total sample of n = 7 154 (3 866 women and 3 288 men) for works using University of Pennsylvania Smell Identification Test (UPSIT). We conducted separate meta-analyses for each aspect of olfaction: identification, discrimination and threshold. The results of our meta-analysis indicate that women generally outperform men in olfactory abilities. What is more, they do so in every aspect of olfaction analyzed in the current study. However, the effect sizes were weak and ranged between g = 0.08 and g = 0.30. We discuss our findings in the context of factors that potentially shape sex differences in olfaction. Nevertheless, although our findings seem to confirm the "common knowledge" on female olfactory superiority, it needs to be emphasized that the effect sizes we observed were notably small.

Psycholinguistic variables matter in odor naming

People from Western societies generally find it difficult to name odors. In trying to explain this, the olfactory literature has proposed several theories that focus heavily on properties of the odor itself but rarely discuss properties of the label used to describe it. However, recent studies show speakers of languages with dedicated smell lexicons can name odors with relative ease. Has the role of the lexicon been overlooked in the olfactory literature? Word production studies show properties of the label, such as word frequency and semantic context, influence naming; but this field of research focuses heavily on the visual domain. The current study combines methods from both fields to investigate word production for olfaction in two experiments. In the first experiment, participants named odors whose veridical labels were either high-frequency or low-frequency words in Dutch, and we found that odors with high-frequency labels were named correctly more often. In the second experiment, edibility was used for manipulating semantic context in search of a semantic interference effect, presenting the odors in blocks of edible and inedible odor source objects to half of the participants. While no evidence was found for a semantic interference effect, an effect of word frequency was again present. Our results demonstrate psycholinguistic variables—such as word frequency—are relevant for olfactory naming, and may, in part, explain why it is difficult to name odors in certain languages. Olfactory researchers cannot afford to ignore properties of an odor’s label.

On the Communicative Function of Body Odors

Humans use multiple senses to navigate the social world, and the sense of smell is arguably the most underestimated one. An intriguing aspect of the sense of smell is its social communicative function. Research has shown that human odors convey information about a range of states (e.g., emotions, sickness) and traits (e.g., individuality, gender). Yet, what underlies the communicability of these states and traits via smell? We fill this explanatory gap with a framework that highlights the dynamic and flexible aspects of human olfactory communication. In particular, we explain how chemical profiles, associative learning (i.e., the systematic co-occurrence of chemical profiles with state- or trait-related information), and top-down contextual influences could interact to shape human odor perception. Our model not only helps to integrate past research on human olfactory communication but it also opens new avenues for future research on this fascinating, yet to date poorly understood, field.

Influence of Fragrances on Human Psychophysiological Activity: With Special Reference to Human Electroencephalographic Response

The influence of fragrances such as perfumes and room fresheners on the psychophysiological activities of humans has been known for a long time, and its significance is gradually increasing in the medicinal and cosmetic industries. A fragrance consists of volatile chemicals with a molecular weight of less than 300 Da that humans perceive through the olfactory system. In humans, about 300 active olfactory receptor genes are devoted to detecting thousands of different fragrance molecules through a large family of olfactory receptors of a diverse protein sequence. The sense of smell plays an important role in the physiological effects of mood, stress, and working capacity. Electrophysiological studies have revealed that various fragrances affected spontaneous brain activities and cognitive functions, which are measured by an electroencephalograph (EEG). The EEG is a good temporal measure of responses in the central nervous system and it provides information about the physiological state of the brain both in health and disease. The EEG power spectrum is classified into different frequency bands such as delta (0.5-4 Hz), theta (4-8 Hz), alpha (8-13 Hz), beta (13-30 Hz) and gamma (30-50 Hz), and each band is correlated with different features of brain states. A quantitative EEG uses computer software to provide the topographic mapping of the brain activity in frontal, temporal, parietal and occipital brain regions. It is well known that decreases of alpha and beta activities and increases of delta and theta activities are associated with brain pathology and general cognitive decline. In the last few decades, many scientific studies were conducted to investigate the effect of inhalation of aroma on human brain functions. The studies have suggested a significant role for olfactory stimulation in the alteration of cognition, mood, and social behavior. This review aims to evaluate the available literature regarding the influence of fragrances on the psychophysiological activities of humans with special reference to EEG changes.

Odour Perception: An Object-Recognition Approach

Object recognition is a crucial component of both visual and auditory perception. It is also critical for olfaction. Most odours are composed of 10s or 100s of volatile components, yet they are perceived as unitary perceptual events against a continually shifting olfactory background (ie figure—ground segregation). We argue here that this occurs by rapid central adaptation to background odours combined with a pattern-matching system to recognise discrete sets of spatial and temporal olfactory features—an odour object. We present supporting neuropsychological, learning, and developmental evidence and then describe the neural circuitry which underpins this. The vagaries of an object-recognition approach are then discussed, with emphasis on the putative importance of memory, multimodal representations, and top—down processing.

Odor Emotional Quality Predicts Odor Identification

It is commonly agreed upon a strong link between emotion and olfaction. Odor-evoked memories are experienced as more emotional compared with verbal, visual, and tactile stimuli. Moreover, the emotional quality of odor cues increases memory performance, but contrary to this, odors are poor retrieval cues for verbal labels. To examine the relation between the emotional quality of an odor and its likelihood of identification, this study evaluates how normative emotion ratings based on the 3-dimensional affective space model (that includes valence, arousal, and dominance), using the Self-Assessment Manikin by Bradley and Lang (Bradley MM, Lang PJ. 1994. Measuring emotion: the Self-Assessment Manikin and the Semantic Differential. J Behav Ther Exp Psychiatry. 25(1):49-59.) and the Positive and Negative Affect Schedule (Watson D, Clark LA, Tellegen A. 1988. Development and validation of brief measures of positive and negative affect: the PANAS scales. J Pers Soc Psychol. 54(6):1063-1070.) predict the identification of odors in a multiple choice condition. The best fitting logistic regression model includes squared valence and dominance and thus, points to a significant role of specific emotional features of odors as a main clue for odor identification.

The muted sense: neurocognitive limitations of olfactory language

Most people find it profoundly difficult to name familiar smells. This difficulty persists even when perceptual odor processing and visual object naming are unimpaired, implying deficient sensory-specific interactions with the language system. Here we synthesize recent behavioral and neuroimaging data to develop a biologically informed framework for olfactory lexical processing in the human brain. Our central premise is that the difficulty in naming common objects through olfactory (compared with visual) stimulation is the end result of cumulative effects occurring at three successive stages of the olfactory language pathway: object perception, lexical-semantic integration, and verbalization. Understanding the neurocognitive mechanisms by which the language network interacts with olfaction can yield unique insights into the elusive nature of olfactory naming.

A Sniff of Happiness

It is well known that feelings of happiness transfer between individuals through mimicry induced by vision and hearing. The evidence is inconclusive, however, as to whether happiness can be communicated through the sense of smell via chemosignals. As chemosignals are a known medium for transferring negative emotions from a sender to a receiver, we examined whether chemosignals are also involved in the transmission of positive emotions. Positive emotions are important for overall well-being and yet relatively neglected in research on chemosignaling, arguably because of the stronger survival benefits linked with negative emotions. We observed that exposure to body odor collected from senders of chemosignals in a happy state induced a facial expression and perceptual-processing style indicative of happiness in the receivers of those signals. Our findings suggest that not only negative affect but also a positive state (happiness) can be transferred by means of odors.

Rapid stress system drives chemical transfer of fear from sender to receiver

Humans can register another person's fear not only with their eyes and ears, but also with their nose. Previous research has demonstrated that exposure to body odors from fearful individuals elicited implicit fear in others. The odor of fearful individuals appears to have a distinctive signature that can be produced relatively rapidly, driven by a physiological mechanism that has remained unexplored in earlier research. The apocrine sweat glands in the armpit that are responsible for chemosignal production contain receptors for adrenalin. We therefore expected that the release of adrenalin through activation of the rapid stress response system (i.e., the sympathetic-adrenal medullary system) is what drives the release of fear sweat, as opposed to activation of the slower stress response system (i.e., hypothalamus-pituitary-adrenal axis). To test this assumption, sweat was sampled while eight participants prepared for a speech. Participants had higher heart rates and produced more armpit sweat in the fast stress condition, compared to baseline and the slow stress condition. Importantly, exposure to sweat from participants in the fast stress condition induced in receivers (N = 31) a simulacrum of the state of the sender, evidenced by the emergence of a fearful facial expression (facial electromyography) and vigilant behavior (i.e., faster classification of emotional facial expressions).

The impact of expertise in olfaction

Olfactory expertise remains poorly understood, most likely because experts in odor, such as perfumers, sommeliers, and oenologists, are much rarer than experts in other modalities, such as musicians or sportsmen. In this review, we address the specificities of odor expertise in both odor experts and in a priori untrained individuals who have undergone specific olfactory training in the frame of an experiment, such as repeated exposure to odors or associative learning. Until the 21st century, only the behavioral effects of olfactory training of untrained control individuals had been reported, revealing an improvement of olfactory performance in terms of sensitivity, discrimination, memory, and identification. Behavioral studies of odor experts have been scarce, with inconsistent or inconclusive results. Recently, the development of cerebral imaging techniques has enabled the identification of brain areas and neural networks involved in odor processing, revealing functional and structural modifications as a function of experience. The behavioral approach to odor expertise has also evolved. Researchers have particularly focused on odor mental imagery, which is characteristic of odor experts, because this ability is absent in the average person but is part of a perfumer’s professional practice. This review summarizes behavioral, functional, and structural findings on odor expertise. These data are compared with those obtained using animals subjected to prolonged olfactory exposure or to olfactory-enriched environments and are discussed in the context of functional and structural plasticity.

Olfactory performance is predicted by individual sex-atypicality, but not sexual orientation

Many previous studies have reported robust sex differences in olfactory perception. However, both men and women can be expected to vary in the degree to which they exhibit olfactory performance considered typical of their own or the opposite sex. Sex-atypicality is often described in terms of childhood gender nonconformity, which, however, is not a perfect correlate of non-heterosexual orientation. Here we explored intrasexual variability in psychophysical olfactory performance in a sample of 156 individuals (83 non-heterosexual) and found the lowest odor identification scores in heterosexual men. However, when childhood gender nonconformity was entered in the model along with sexual orientation, better odor identification scores were exhibited by gender-nonconforming men, and greater olfactory sensitivity by gender-conforming women, irrespective of their sexual orientation. Thus, sex-atypicality, but not sexual orientation predicts olfactory performance, and we propose that this might not be limited to olfaction, but represent a more general phenomenon.

A cortical pathway to olfactory naming: evidence from primary progressive aphasia

It is notoriously difficult to name odours. Without the benefit of non-olfactory information, even common household smells elude our ability to name them. The neuroscientific basis for this olfactory language 'deficit' is poorly understood, and even basic models to explain how odour inputs gain access to transmodal representations required for naming have not been put forward. This study used patients with primary progressive aphasia, a clinical dementia syndrome characterized by primary deficits in language, to investigate the interactions between olfactory inputs and lexical access by assessing behavioural performance of olfactory knowledge and its relationship to brain atrophy. We specifically hypothesized that the temporal pole would play a key role in linking odour object representations to transmodal networks, given its anatomical proximity to olfactory and visual object processing areas. Behaviourally, patients with primary progressive aphasia with non-semantic subtypes were severely impaired on an odour naming task, in comparison with an age-matched control group. However, with the availability of picture cues or word cues, odour matching performance approached control levels, demonstrating an inability to retrieve but not to recognize the name and nature of the odorant. The magnitude of cortical thinning in the temporal pole was found to correlate with reductions in odour familiarity and odour matching to visual cues, whereas the inferior frontal gyrus correlated with both odour naming and matching. Volumetric changes in the mediodorsal thalamus correlated with the proportion of categorical mismatch errors, indicating a possible role of this region in error-signal monitoring to optimize recognition of associations linked to the odour. A complementary analysis of patients with the semantic subtype of primary progressive aphasia, which is associated with marked temporopolar atrophy, revealed much more pronounced impairments of odour naming and matching. In identifying the critical role of the temporal pole and inferior frontal gyrus in transmodal linking and verbalization of olfactory objects, our findings provide a new neurobiological foundation for understanding why even common odours are hard to name.

Binaral rivalry in the presence of visual perceptual and semantic influences

When two different odorants are presented simultaneously to the two nostrils, we experience alternations in olfactory percepts, a phenomenon called binaral rivalry. Little is known about the nature of such alternations. Here we investigate this issue by subjecting unstable and stable olfactory percepts to the influences of visual perceptual or semantic cues as participants engage in simultaneous samplings of either two different odorants (binaral) or a single odorant and water (mononaral), one to each nostril. We show that alternations of olfactory percepts in the binaral setting persist in the presence of visual perceptual and semantic modulations. We also show that perceptual cues have a stronger effect than semantic cues in the binaral case, whereas their effects are comparable in the mononaral setting. Our findings provide evidence that an inherent, stimulus-driven process underlies binaral rivalry despite its general susceptibility to top-down influences.

Genetic and environmental influences on odor identification ability in the very old

Odor identification ability and cognition were measured in a population-based cohort of 1,222 very old twins and singletons, including 91 centenarians. Heritability for identifying odors was low, in contrast to that for cognition. Common genes were found to contribute to both olfaction and cognition. In a multiple regression model, sex, age, cognitive function, and smoking, but not APOEε4 status, were significant predictors of the olfactory test scores (all ps < 0.001). This study, along with data from other studies, suggests that indices of heritability for odor identification decline with age, likely reflecting adverse environmental influences on the smell system.

Differential effects of active attention and age on event-related potentials to visual and olfactory stimuli

Normal aging impairs olfactory functioning both centrally and peripherally. The P3 peak of the event-related potential (ERP), evoked by active response to a target stimulus, is considered a reflection of central cognitive processing. It can also be evoked in a passive task to both auditory and visual stimuli. Our goal was to investigate whether age influences amplitude and latency of the ERP differentially in active and passive tasks to olfactory stimuli. Olfactory and visual event-related potentials were elicited with a single stimulus paradigm in separate active and passive task response conditions. Participants included 30 healthy individuals from three age groups, young, middle age, and older adults. Results indicated that P3 ERP latency increased with age in both sensory modalities. P3 latencies for active versus passive tasks were similar across age groups for visual ERPs, but in the olfactory modality, older adults demonstrated significantly longer latencies in the passive task compared to the active task. Future directions should include research on specific clinical populations utilizing active versus passive task conditions.

Odours influence visually induced emotion: behavior and neuroimaging

The present study was conducted to investigate the influence of olfaction on subjective valence intensity ratings of visual presentations. Pictures of five different categories (baby, flower, erotic, fear and disgust) were presented each being associated with five different odour conditions [no odour, low and high concentrations of phenylethyl alcohol (positive odour) and low and high concentrations of hydrogen sulphide (negative odour)]. Study participants had to rate the emotional content of each picture with respect to valence and intensity while brain activities were recorded with a whole-cortex magnetoencephalograph (MEG). A significant interaction between odour condition and picture category with respect to rating performance was found. In particular, positive valence intensity ratings related to flowers were increased in positive and negative odour conditions. Negative valence intensity ratings related to disgusting pictures were also increased in positive and negative odour conditions. The only decrease was found in the baby category in the high concentration negative odour condition. No behavioural effects were found for the categories erotic and fear. Around 300 ms after stimulus onset odour-related brain activity effects were found for all picture categories. On the other hand, around 700 ms after stimulus onset odour-related brain activity effects occurred only in the flower, fear and disgust picture categories. We interpret that early information processing demonstrates more pronounced olfactory and visually induced emotion interaction than later information processing. Since the early time window more likely reflects subconscious information processing we interpret that interaction between olfaction and visually induced emotion mostly occurs below the level of consciousness. Later, rather conscious information processing, seems to be differently influenced by simultaneous olfaction depending on the kind of emotion elicited through the sense of vision.

An odor is not worth a thousand words: from multidimensional odors to unidimensional odor objects

Olfaction is often referred to as a multidimensional sense. It is multidimensional in that approximately 1000 different receptor types, each tuned to particular odor aspects, together contribute to the olfactory percept. In humans, however, this percept is nearly unidimensional. Humans can detect and discriminate countless odorants, but can identify few by name. The one thing humans can and do invariably say about an odor is whether it is pleasant or not. We argue that this hedonic determination is the key function of olfaction. Thus, the boundaries of an odor object are determined by its pleasantness, which--unlike something material and more like an emotion--remains poorly delineated with words.

Comparing Mental Imagery across the Sensory Modalities

Previous studies using introspective reports have suggested that although mental images can contain elements referring to all sensory modalities, visual images tend to be experienced as most vivid, whereas olfactory and gustatory images tend to be least vivid. However, these studies have typically used arbitrarily selected events and objects as the to-be-imagined stimuli, which may have biased cross-modal comparison. Therefore, in the present study participants were instructed to imagine an event or product of their choice that elicited a conspicuous or characteristic appearance, sound, feel, smell, or taste. The results showed that the types of events imagined differed considerably across modalities. Similar to previous studies in this area, we found that the reported image quality was consistently highest for vision and audition, and lowest for smell.

Olfactory identification in non-demented elderly population and in mild cognitive impairment: a comparison of performance in clinical odor identification versus Boston Naming Test

Performance in olfactory identification was studied in mild cognitive impairment (MCI), using slightly expanded standard clinical approach to study the olfactory nerve. Four hundred and eighty-six cognitively normal individuals and 72 individuals with MCI underwent spontaneous and cued odor identification and delayed odor recall. Performance in these was compared with the performance in the CERAD version of the Boston Naming Test (BNT). The individuals with MCI scores significantly worse in all tests compared with controls, but the performance in tests assessing odor were less impaired than performance in the BNT. Standard assessment of olfactory nerve function is not sufficient to study cognitive impairment in MCI.

Non-linear quantitative electroencephalographic (qEEG) changes during processing of chemo-sensory stimulations: a preliminary study

The present study was to investigate the processing of pleasant smell and taste stimuli by non-linear EEG measures. Point correlation dimension (PD2i) has been used for studying the local, and synchronization likelihood (SL) the global dynamical organization. Nine healthy subjects participated in this study. After a baseline period of 30s the patients were given a perfume cap or a chocolate taste for 30s. The analysis was performed off-line on 16 channels. After smell stimulation an immediate bilateral but short response was seen. First a decrease and afterwards an increase were found in the mean PD2i. In contrast, the taste stimulation resulted in a later reaction mainly on the right side. The SL in the slow alpha band decreased during the first 15s after both stimulations. In the second 15s, however, a remarkable SL increase was seen mainly in the 7-14Hz and in every frequency band. The decreased mean PD2i and SL values could be interpreted by the simplified network preparation to cognitive data processing. The PD2i and SL methods detected subtle dynamical changes during olfactory and gustatory processes suitable for collection normative database to pathological conditions.

Estrogen replacement therapy induces functional asymmetry on an odor memory/discrimination test

The secondary afferents of the olfactory system largely project to the ipsilateral cortex without synapsing in the thalamus, making unilateral olfactory testing a useful probe of ipsilateral hemispheric activity. In light of evidence that lateralized performance on some perceptual tasks may be influenced by estrogen, we assessed left:right nostril differences in two measures of olfactory function in 14 post-menopausal women receiving estrogen replacement therapy (ERT) and 48 post-menopausal women receiving no such therapy. Relative to women not taking ERT, those receiving ERT exhibited better performance in the left nostril and poorer performance in the right nostril on an odor memory/discrimination test. Similar laterality effects were not observed for an odor detection threshold test employing phenyl ethyl alcohol. These results suggest that estrogen influences the lateralization of an odor memory/discrimination task and that hormone replacement therapy in the menopause may be an excellent paradigm for understanding lateralizing effects of hormones on some sensory processes.

Difficulty in evoking odor images: the role of odor naming

Many studies report that people have difficulty in evoking odor images. In this article, we explore whether this results from another commonly observed phenomenon, difficulty in naming odors. In Experiment 1, participants both named and attempted to imagine either odors or their common visual referents. More-difficult-to-name odors were reported as being more difficult to evoke as olfactory images, in comparison with the visual condition. In Experiment 2, participants received training prior to forming odor images and naming the same set of odors. As in Experiment 1, more-difficult-to-name odors were harder to imagine, but participants who had learned the odor names during training were significantly better, by their own report, at imagining many of these stimuli, relative to participants who were either exposed to the odors, exposed to their names, or who received no pretraining. In sum, these experiments suggest that odor naming may account for some of the difficulty reported by participants when attempting to evoke odor images; we discuss an associative basis for this effect.

Smell images and the flavour system in the human brain

Flavour perception is one of the most complex of human behaviours. It involves almost all of the senses, particularly the sense of smell, which is involved through odour images generated in the olfactory pathway. In the human brain, the perceptual systems are closely linked to systems for learning, memory, emotion and language, so distributed neural mechanisms contribute to food preference and food cravings. Greater recognition of the role of the brain's flavour system and its connection with eating behaviour is needed for a deeper understanding of why people eat what they do, and to generate better recommendations about diet and nutrition.

The influence of stimulus duration on odor perception

Although different parameters are known to alter the shape of olfactory event related potentials (ERP), ERP parameters are generally thought to be independent from stimulus duration. Evidence from recent studies investigating trigeminal ERP indicates that this may not be true. Aim of the present study was to investigate the relationship of stimulus duration and ERP. A total of 20 young healthy subjects participated. Subjects were investigated on 5 occasions on 5 different days. ERP were recorded to olfactory stimuli of two different concentrations and 3 different durations (100 ms, 200 ms, 300 ms). In two sessions olfactory ERP to PEA were recorded, in another two sessions H2S was applied. During the same sessions, intensity ratings were recorded. In the fifth session, subjects were asked to rate the duration of H2S stimuli and PEA stimuli. Whereas at weak stimulus concentrations no effect of stimulus duration could be observed, there was a clear effect of "duration" in ERP amplitudes following stimuli with higher concentrations: the longer the stimulus duration the larger the ERP amplitudes. No effect was found on ERP latencies. With regard to intensity ratings, strong stimuli and longer lasting stimuli lead to higher ratings. Similarly, ratings of stimulus duration were dependent from stimulus concentration and stimulus duration. Results of the present study showed that similar to trigeminal ERP, information about stimulus duration is encoded in olfactory ERP, mainly in amplitudes.

The human brain is a detector of chemosensorily transmitted HLA-class I-similarity in same- and opposite-sex relations

Studies on subjective body odour ratings suggest that humans exhibit preferences for human leucocyte antigen (HLA)-dissimilar persons. However, with regard to the extreme polymorphism of the HLA gene loci, the behavioural impact of the proposed HLA-related attracting signals seems to be minimal. Furthermore, the role of HLA-related chemosignals in same- and opposite-sex relations in humans has not been specified so far. Here, we investigate subjective preferences and brain evoked responses to body odours in males and females as a function of HLA similarity between odour donor and smeller. We show that pre-attentive processing of body odours of HLA-similar donors is faster and that late evaluative processing of these chemosignals activates more neuronal resources than the processing of body odours of HLA-dissimilar donors. In same-sex smelling conditions, HLA-associated brain responses show a different local distribution in male (frontal) and female subjects (parietal). The electrophysiological results are supported by significant correlations between the odour ratings and the amplitudes of the brain potentials. We conclude that odours of HLA-similar persons function as important social warning signals in inter- and intrasexual human relations. Such HLA-related chemosignals may contribute to female and male mate choice as well as to male competitive behaviour.

Temporal pattern of odor administration alters hemispheric processing in humans

Evidence from a variety of sensory modalities has suggested that the left hemisphere may be 'tuned' to process more rapidly changing stimuli than the right and some have suggested that this difference forms the foundation of the functional dichotomy often drawn between the two hemispheres. Odors may be thought to engage these same temporally dependent processes as portions of an odor mixture may come to be transduced into a phasic series of neural events. Using brain electrical activity, we show that the temporal sequence of the odor alters the pattern of brain electrical activity. Estimates of the source localization for this activity indicate that rapidly changing odors, like sounds, visual and tactile stimuli, show increased activity in the left hemisphere.

Olfactory imagery: a review

Olfaction's unique cognitive architecture, the apparently inconsistent evidence favoring imagery, and its difficulty of evocation have led some to conclude that there is no capacity for olfactory imagery. Using three streams of evidence, we examine the validity of this claim. First, self-reports of olfactory imagery can resemble those obtained for actual perception. Second, imagining an odor can produce effects similar to actual perception. Third, olfactory perception and memory-based images can interact. A model of olfactory imagery is then presented that utilizes the same systems employed in actual perception, with similar constraints. This model is consistent with olfaction's unique information-processing capacities and can account for previous experimental inconsistencies on the basis of difficulty of evocation, a consequence of unstable access to semantic information. In sum, the evidence presented here is favorable to the existence of an olfactory imagery capacity.

Capturing product experiences: a split-modality approach

When people interact with products, all sensory modalities are open to receive information. To assess each modality's potential contribution to overall product experiences, we developed a split-modality approach, in which subjects experienced real-life products through only one modality: vision, touch, audition, or olfaction. Responses focused on (1) description of the sensory experience, (2) product identification, and (3) descriptions of associations and memories linked to this experience. Visual and tactual information were most detailed, made product identification easiest, and yielded the clearest memories of past events, associations to persons, and associations with other products. Because vision may have an advantage over touch by the speed with which information is processed, vision is likely to dominate product experiences in real-life situations.

Olfactory Dreams: Phenomenology, Relationship to Volitional Imagery and Odor Identification

Phenomenological evidence for olfactory sensation in the absence of appropriate stimulation—imagery—is inconclusive and draws most support from reports of olfactory hallucinations. The current study examined whether more convincing phenomenological evidence could be obtained from normal participants, by studying reports of their olfactory dreams. A questionnaire approach ( N = 284) revealed that olfactory dreams were uncommon, had features similar to actual olfaction (emotive and brief), were representative of odors encountered in everyday life, and were positively related to self-report volitional imagery ability. In addition, a sub-group ( N = 116) also completed an odor identification test. Participants who experienced olfactory dreams were significantly better at identifying odors, an effect not mediated by motivational or attentional factors. These findings suggest people can experience olfactory images although their occurrence may be governed by the strength of connections between olfactory and semantic memory—notoriously weak in olfaction.

Performance in a complex task and breathing under odor exposure

We investigated the influences of odor exposure on performance and on breathing measures. The task was composed of tracking, short-term memory, and peripheral reaction parts. During rest or while performing the task, 12 participants were exposed to 4 different odors in 2 intensities. The higher intensity of the malodors induced a short-term decrement in mean inspiration flow (Vi/Ti) after stimulus onset and impaired performance in the short-term memory task, as compared with control trials; no effect was found for the positively judged odors. The study suggests that a distractor as simple as a bad smell may pull a person off task, however briefly, and may result in a detriment to performance. Actual or potential applications of this research involve designing or securing tasks in such a way that a brief withdrawal of attention does not have fatal consequences.

Convergent and divergent effects of odors and emotions in depression

The aim of the present study was to investigate the similarities and differences in the olfactory and visual processing of emotional stimuli in healthy subjects and in patients with major depressive disorder (MDD). Twenty-five inpatients were investigated after admission to the psychiatric clinic. Fifteen of them participated a second time, shortly before their discharge from the hospital. A group of healthy subjects, matched according to age and sex, served as a control. Chemsosensory event-related potentials (CSERPs) were recorded using the constant flow method. In addition, event-related potentials (ERPs), in response to colors and emotional slides, were obtained to control modality and emotion-specific effects. The subjects' task was to discriminate the colors (red/yellow) and odors (phenyl-ethylalcohol = rose/ isobutyraldehyde = rotten butter) according to their quality and to judge the valence of the emotional slides (IAPS slides). The EEG was recorded from 32 scalp locations. At the beginning of the therapy, visual stimulus processing was attenuated in depressive subjects at a relatively late processing level (reduced amplitudes of the P3 and pSW in response to colors and emotional slides), whereas olfactory stimulus processing had already been affected at an early level (reduced amplitudes of the P2 and P3-1 peaks in MDD patients). However, after successful medical treatment, ERPs did not differentiate between depressive patients and healthy controls. We discuss whether functional deviations within the primary olfactory cortex are responsible for the lower olfactory sensitivity, as well as for the altered emotional stimulus processing in MDD patients.

Olfaction and face encoding in humans: a magnetoencephalographic study

Magnetic field changes were recorded while 20 healthy young participants performed a deep face encoding task. Some of the faces were randomly associated with a simultaneously presented odor. A recognition test, during which all faces were presented again together with the same number of new faces, followed. The task was to discriminate between repeated and new faces. During the recognition test no odor was presented. The recognition performance was significantly influenced by the simultaneously associated odor during the encoding phase. Faces associated with odor were less accurately recognized. In addition, we found significant physiological differences between 'encoded faces without odor' and 'encoded faces with odor'. In particular, two effects occurred. Between about 200 and 300 ms after stimulus onset 'encoded faces without odor' evoked higher brain activity than 'encoded faces with odor'. Between about 600 and 900 ms after stimulus onset 'encoded faces with odor' evoked higher brain activity than 'encoded faces without odor'. Whereas the latter effect is interpreted as reflecting conscious olfactory information processing, the earlier effect is suggested to reflect an odor influence on face encoding. We suggest that the simultaneous odor association distracted face encoding resulting in a significantly reduced recognition performance. These findings are suggested to represent evidence of multimodal sensoric interactions between visual face processing and olfactory information.