Facial and autonomic responses to biological and artificial olfactory stimuli in human neonates: re-examining early hedonic discrimination of odors

Olfactory stimulation in newborns: Regional differences in cerebral oxygenation

BACKGROUND

The sense of smell is fully developed in newborns and plays an important role in their early development. There are several approaches to studying olfactory processing in the newborn brain, including EEG, fMRI, and near-infrared spectroscopy (NIRS). Understanding the processing of olfactory stimuli in the newborn brain is of fundamental importance for the development of supportive therapeutic odorant delivery, e.g. for weaning by gavage, and for adapting it to the developing brain. This study aimed to investigate the effect of different odors (milk, farnesol odor, and water as a control) on changes in brain activation in newborns in two different brain regions.

METHODS

Newborns older than 72 h and below an age of seven days were divided into two groups with different optode positioning strategies of NIRS, group I parietal and group II frontal. Olfactory stimulation was administered using milk, farnesol (floral odor), and water as a control.

RESULTS

A total of 26 newborns participated in the study. In the final analysis, 19 children were included. Allthough the optode positioning does not differ significantly, in group I, farnesol stimulation resulted in a significant increase in oxygenated hemoglobin compared to the control, while milk odor showed a decreased amplitude, particularly in the more parietal optode position. In group II, a significant difference was observed between the milk odor and the control, in the frontal areas.

CONCLUSIONS

This study revealed significant changes in hemoglobin oxygenation, indicating neuronal activation following different olfactory stimulation in both optode positionings. Whereas milk had more impact in frontal areas, the floral odor caused an effect in parietal areas.

Olfaction modulates cortical arousal independent of perceived odor intensity and pleasantness

Throughout history, various odors have been harnessed to invigorate or relax the mind. The mechanisms underlying odors' diverse arousal effects remain poorly understood. We conducted five experiments (184 participants) to investigate this issue, using pupillometry, electroencephalography, and the attentional blink paradigm, which exemplifies the limit in attentional capacity. Results demonstrated that exposure to citral, compared to vanillin, enlarged pupil size, reduced resting-state alpha oscillations and alpha network efficiency, augmented beta-gamma oscillations, and enhanced the coordination between parietal alpha and frontal beta-gamma activities. In parallel, it attenuated the attentional blink effect. These effects were observed despite citral and vanillin being comparable in perceived odor intensity, pleasantness, and nasal pungency, and were unlikely driven by semantic biases. Our findings reveal that odors differentially alter the small-worldness of brain network architecture, and thereby brain state and arousal. Furthermore, they establish arousal as a unique dimension in olfactory space, distinct from intensity and pleasantness.

Effects of vanilla odor on hypoxia-related periodic breathing in premature newborns: A pilot study

BACKGROUND

Periodic breathing (PB)-related intermittent hypoxia can have long-lasting deleterious consequences in preterm infants. Olfactory stimulation using vanilla odor is beneficial for apnea of prematurity in the first postnatal days/weeks. We aimed to determine for the first time whether vanilla odor can also decrease PB-related intermittent hypoxia.

METHOD

This pilot study was a balanced crossover clinical trial including 27 premature infants born between 30 and 33+6 weeks of gestation. We performed 12-h recordings on two nights separated by a 24-h period. All infants were randomly exposed to vanilla odor on the first or second study night. The primary outcome was the desaturation index, defined as the number per hour of pulse oximetry (SpO2) values <90 % for at least 5 s, together with a drop of ≥5 % from the preceding value. Univariate mixed linear models were used for the statistical analysis.

RESULTS

Overall, exposure to vanilla odor did not significantly decrease the desaturation index (52 ± 22 events/h [mean ± SD] on the intervention night vs. 57 ± 26, p = 0.2); furthermore, it did not significantly alter any secondary outcome. In a preliminary post hoc subgroup analysis, however, the effect of vanilla odor was statistically significant in infants with a desaturation index of ≥70/h (from 86 ± 12 to 65 ± 23, p = 0.04).

CONCLUSION

In this pilot study, vanilla odor overall did not decrease PB-related intermittent hypoxia in infants born at 30-33+6 weeks of gestation, which is when they are close to term. Preliminary results suggesting a beneficial effect in infants with the highest desaturation index, however, justify further studies in the presence of PB-related intermittent hypoxia as well as in infants born more prematurely.

Testing detectability, attractivity, hedonic specificity, extractability, and robustness of colostrum odor-Toward an olfactory bioassay for human neonates

Human milk odor is attractive and appetitive for human newborns. Here, we studied behavioral and heart-rate (HR) responses of 2-day-old neonates to the odor of human colostrum. To evaluate detection in two conditions of stimulus delivery, we first presented the odor of total colostrum against water. Second, the hedonic specificity of total colostrum odor was tested against vanilla odor. Third, we delivered only the fresh effluvium of colostrum separated from the colostrum matrix; the stability of this colostrum effluvium was then tested after deep congelation; finally, after sorptive extraction of fresh colostrum headspace, we assessed the activity of colostrum volatiles eluting from the gas chromatograph (GC). Regardless of the stimulus-delivery method, neonates displayed attraction reactions (HR decrease) as well as appetitive oral responses to the odor of total colostrum but not to vanilla odor. The effluvium separated from the fresh colostrum matrix remained appetitive but appeared labile under deep freezing. Finally, volatiles from fresh colostrum effluvium remained behaviorally active after GC elution, although at lower magnitude. In sum, fresh colostrum effluvium and its eluate elicited a consistent increase in newborns' oral activity (relative to water or vanilla), and they induced shallow HR decrease. Newborns' appetitive oral behavior was the most reproducible response criterion to the effluvium of colostrum. In conclusion, a set of unidentified volatile compounds from human colostrum is robust enough after extraction from the original matrix and chromatographic processing to continue eliciting appetitive responses in neonates, thus opening new directions to isolate and assay specific volatile molecules of colostrum.

How do human newborns come to understand the multimodal environment?

For a long time, newborns were considered as human beings devoid of perceptual abilities who had to learn with effort everything about their physical and social environment. Extensive empirical evidence gathered in the last decades has systematically invalidated this notion. Despite the relatively immature state of their sensory modalities, newborns have perceptions that are acquired, and are triggered by, their contact with the environment. More recently, the study of the fetal origins of the sensory modes has revealed that in utero all the senses prepare to operate, except for the vision mode, which is only functional starting from the first minutes after birth. This discrepancy between the maturation of the different senses leads to the question of how human newborns come to understand our multimodal and complex environment. More precisely, how the visual mode interacts with the tactile and auditory modes from birth. After having defined the tools that newborns use to interact with other sensory modalities, we review studies across different fields of research such as the intermodal transfer between touch and vision, auditory-visual speech perception, and the existence of links between the dimensions of space, time, and number. Overall, evidence from these studies supports the idea that human newborns are spontaneously driven, and cognitively equipped, to link information collected by the different sensory modes in order to create a representation of a stable world.

Chemosensory continuity from prenatal to postnatal life in humans: A systematic review and meta-analysis

Throughout pregnancy, fetuses are exposed to a range of chemosensory inputs influencing their postnatal behaviors. Such prenatal exposure provides the fetus with continuous sensory information to adapt to the environment they face once born. This study aimed to assess the chemosensory continuity through a systematic review and meta-analysis of existing evidence on chemosensory continuity from prenatal to first postnatal year. Web of Science Core. Collections, MEDLINE, PsycINFO, EBSCOhost ebook collection was searched from 1900 to 2021. Studies identified from the search were grouped according to type of stimuli the fetuses were exposed to prenatally that the neonatal infants' responses to were being evaluated, namely flavors transferred from the maternal diet, and the odor of their own amniotic fluid. Of the 12 studies that met the eligibility criteria for inclusion (k = 6, k = 6, respectively in the first and the second group of studies), and eight studies (k = 4, k = 4, respectively) provided sufficient data suitable for meta-analysis. Infants, during their first year of life, oriented their heads for significantly longer durations in the direction of the prenatally experienced stimuli with large pooled effect sizes (flavor stimuli, d = 1.24, 95% CI [0.56, 1.91]; amniotic fluid odor, d = 0.853; 95% CI [.632, 1.073]). The pooled effect size for the duration of mouthing behavior was significant in response to prenatal flavor exposure through maternal diet (d = 0.72; 95% CI [0.306, 1.136]), but not for the frequency of negative facial expressions (d = -0.87, 95% CI [-2.39, 0.66]). Postnatal evidence suggests that there is a chemosensory continuity from fetal to the first year of postnatal life.

Impact of diet on sensory processing in early childhood: summary of an interactive webconference / expert roundtable discussion

Pediatric feeding disorders can be seen in up to 45% of normally developing children aged under 5 years old, mainly during the first three years of life when the child has inadequate food intake and/or difficulty maintaining adequate growth, and/or lack of age-appropriate eating habit. This article describes the opinion of a group of experts on children eating patterns and how to manage pediatric feeding disorders, with the aim to improve the quality of life of children and their caregivers.

Flavor Wheel Construction and Sensory Profile Description of Human Milk

To explore the flavor characteristics of human milk, we constructed a three-tiered human milk flavor wheel based on 53 sensory descriptors belonging to different sensory categories. Fifteen sensory descriptors were selected using M-value and multivariate statistical methods, and the corresponding references were set up to realize qualitative and quantitative sensory evaluation of the human milk samples. To ensure the accuracy and reliability of the sensory evaluation, the performance of the sensory panelists was also tested. The sensory profile analysis indicated that the established sensory descriptors could properly reflect the general sensory properties of the human milk and could also be used to distinguish different samples. Further investigation exposed that the fat content might be an important factor that influence the sensory properties of human milk. To the best of our knowledge, this is the first report on the flavor wheel of human milk.

Odor Pleasantness Modulates Functional Connectivity in the Olfactory Hedonic Processing Network

Olfactory hedonic evaluation is the primary dimension of olfactory perception and thus central to our sense of smell. It involves complex interactions between brain regions associated with sensory, affective and reward processing. Despite a recent increase in interest, several aspects of olfactory hedonic evaluation remain ambiguous: uncertainty surrounds the communication between, and interaction among, brain areas during hedonic evaluation of olfactory stimuli with different levels of pleasantness, as well as the corresponding supporting oscillatory mechanisms. In our study we investigated changes in functional interactions among brain areas in response to odor stimuli using electroencephalography (EEG). To this goal, functional connectivity networks were estimated based on phase synchronization between EEG signals using the weighted phase lag index (wPLI). Graph theoretic metrics were subsequently used to quantify the resulting changes in functional connectivity of relevant brain regions involved in olfactory hedonic evaluation. Our results indicate that odor stimuli of different hedonic values evoke significantly different interaction patterns among brain regions within the olfactory cortex, as well as in the anterior cingulate and orbitofrontal cortices. Furthermore, significant hemispheric laterality effects have been observed in the prefrontal and anterior cingulate cortices, specifically in the beta ((13–30) Hz) and gamma ((30–40) Hz) frequency bands.

Odour hedonics and the ubiquitous appeal of vanilla

Our food choices and consumption behaviours are often influenced by odour hedonics, especially in the case of those orthonasally experienced aromas (that is, those odours that are food-related). The origins of odour hedonics remain one of the most intriguing puzzles in olfactory science and, over the years, several fundamentally different accounts have been put forwards to try and explain the varying hedonic responses that people have to a wide range of odorants. Associative learning, innate and molecular accounts of odour pleasantness have all been suggested. Here the origins of the hedonic response to vanilla, which is one of the most liked smells cross-culturally, are explored. The history of vanilla's use in food and medicine is outlined, with a focus on its neurocognitive appeal. While vanilla is one of the most widely liked aromas, it is also rated as smelling sweet to most people. Food scientists are becoming increasingly interested in the possibility that such 'sweet smells' could be used to help maintain the sweetness of commercial food products while, at the same time, reducing the use of calorific sweeteners. Such an approach is likely to be facilitated by the low cost of artificial vanilla flavouring (when compared with the high and fluctuating price of natural vanilla pods).

The frontal sharp transient in newborns: An endogenous neurobiomarker concomitant to the physiological and critical transitional period around delivery?

The frontal sharp transient (FST) consists of transient electrical activity recorded around the transitional period from the in to ex utero environment. Although its positive predictive value is assumed, nothing is known about its functionality or origin. The objectives were (i) to define its characteristics and (ii) to develop functional hypothesis. The 128-channels high-resolution electroencephalograms of 20 healthy newborns (37.1-41.6 weeks) were studied. The morphological and time-frequency characteristics of 418 FSTs were analyzed. The source localization of the FSTs was obtained using a finite element head model (5 layers and fontanels) and various source localization methods (distributed and dipolar). The characteristics (duration, slopes, and amplitude) and the localization of FSTs were not modulated by the huge developmental neuronal processes that occur during the very last period of gestation. The sources were located beneath the ventral median part of the frontal lobe around the interhemispheric fissure, suggesting that the olfactory bulbs and orbitofrontal cortex, essential in olfaction and the mother-infant attachment relationship, are likely candidates for the generation of FSTs. FSTs may contribute to the implementation of the functionalities of brain structures involved in the higher-order processing necessary for survival ahead of delivery, with a genetic fingerprint.

A New Perspective of Sustainable Perception: Research on the Smellscape of Urban Block Space

The smell of space is inseparable from the sustainable development of the living environment. The research on olfactory perception and smell landscape has a positive effect on landscape design and urban planning and contributes to the formation and design optimization of unique urban memory. This study combines urban smell tracking experiments with Internet social media data analysis to classify smells in the old city center of Guangzhou, China, and analyzes the study within the inner ring and six historic districts. Based on the research results, the smell map was drawn, and the reliability of the smell map was tested through social data and semantic analysis. The emotional score heat map of smell and emotion in six regions was constructed, highlighting the impact of smell in key neighborhoods on the environment. In the conclusion to the study, the thematic routes of green urban design are proposed: sightseeing routes, cultural routes, and food routes, as well as improvement strategies to promote the integration of smell and urban operation activities and the sustainable development of urban regional characteristics.

Olfactory Stimulation and the Diagnosis of Patients With Disorders of Consciousness: A Double-Blind, Randomized Clinical Trial

OBJECTIVES

The aim of this study was to determine whether behavioral responses elicited by olfactory stimulation are a predictor of conscious behavioral response and prognosis of patients with disorders of consciousness (DOC).

METHODS

Twenty-three DOC patients (8 unresponsive wakefulness syndrome [UWS]; 15 minimally conscious state [MCS]) were recruited for this study in which 1-Octen-3-ol (familiar neutral odor) and pyridine were used to test odor behavioral responses, and water was used as an odorless stimulus. One rater presented the three odors in front of each patient's nose randomly, and another one videotaped all behavioral responses (e.g., pouting, wrinkling nose, slightly shaking head, frowning, etc.). Two independent raters, blind to the stimuli and the patient's diagnosis, gave the behavioral results according to the recorded videos. One-, 3-, and 6-month follow-up evaluations were conducted to obtain a good prognostic value.

RESULTS

All MCS patients showed behavioral responses to the 1-Octen-3-ol stimulus; nine MCS and one UWS showed olfactory emotional responses to the pyridine, and two MCS showed olfactory emotional responses to the water stimulus. The incidence of behavioral response was significantly higher using 1-Octen-3-ol than it was for water by McNemar test (p < 0.001), significantly higher using pyridine than it was for water (p < 0.01). The χ2 test results indicated that there were significant differences between MCS and UWS to 1-Octen-3-ol (p < 0.001). For MCS patients, the incidence of behavioral response was no different between using 1-Octen-3-ol and pyridine (p > 0.05). There was no significant relationship between the olfactory behavioral response and the improvement of consciousness based on the χ2 test analysis (p > 0.05).

CONCLUSION

Olfactory stimuli, especially for the familiar neutral odor, might be effective for eliciting a conscious behavioral response and estimating the clinical diagnosis of DOC patients.

CLINICAL TRIAL REGISTRATION

[https://clinicaltrials.gov/ct2/show/NCT03732092], [identifier NCT03732092].

Identification of new behavioral parameters to assess odorant hedonic value in humans: A naturalistic approach

BACKGROUND

When you smell an odorant, your first reaction will certainly be either I like it or I dislike it. This primary reaction is a reflection of what is called the "hedonic value" of the odor. Very often, this hedonic value dominates the olfactory percept, more than olfactory identification or intensity. This component of olfactory perception is of primary importance for guiding behavior: avoiding danger (the smell of smoke, gas, etc.), consuming food, or seduction. Olfactory hedonics can be assessed using a large number of methods in humans, including psychophysical measures, autonomic responses, measurement of facial expressions or peripheral nervous activity. All of these techniques have their limitations: subjectivity, invasiveness, need for expertise, etc. A NEW METHOD: The olfactory system is closely linked to the reward system, the role of which is to mediate motivated behavior. In this context, we propose that the capacity odorants have of recruiting the reward system and thus inducing motivated behavior can be used to identify new behavioral parameters to assess odor hedonic value in humans.

RESULTS

We recorded freely moving human participants exploring odors emanating from flasks, and showed that five parameters linked to motivated behavior were closely linked to odor hedonics: speed of approach to the nose and withdrawal of the flask containing the odorant, distance between flask and nose, number of samplings, and withdrawal distance (maximal distance between nose and flask after odor sampling).

CONCLUSIONS

We highlighted new non-verbal and non-invasive parameters to evaluate olfactory hedonics in humans based on the assessment of odor-motivated behavior.

Crossmodal Associations with Olfactory, Auditory, and Tactile Stimuli in Children and Adults

People associate information with different senses but the mechanism by which this happens is unclear. Such associations are thought to arise from innate structural associations in the brain, statistical associations in the environment, via shared affective content, or through language. A developmental perspective on crossmodal associations can help determine which explanations are more likely for specific associations. Certain associations with pitch (e.g., pitch-height) have been observed early in infancy, but others may only occur late into childhood (e.g., pitch-size). In contrast, tactile-chroma associations have been observed in children, but not adults. One modality that has received little attention developmentally is olfaction. In the present investigation, we explored crossmodal associations from sound, tactile stimuli, and odor to a range of stimuli by testing a broad range of participants. Across the three modalities, we found little evidence for crossmodal associations in young children. This suggests an account based on innate structures is unlikely. Instead, the number and strength of associations increased over the lifespan. This suggests that experience plays a crucial role in crossmodal associations from sound, touch, and smell to other senses.

The Brainstem-Informed Autism Framework: Early Life Neurobehavioral Markers

Autism spectrum disorders (ASD) have long-term implications on functioning at multiple levels. In this perspective, we offer a brainstem-informed autism framework (BIAF) that traces the protracted neurobehavioral manifestations of ASD to early life brainstem dysfunctions. Early life brainstem-mediated markers involving functions of autonomic/arousal regulation, sleep-wake homeostasis, and sensorimotor integration are delineated. Their possible contributions to the early identification of susceptible infants are discussed. We suggest that the BIAF expands our multidimensional understanding of ASD by focusing on the early involvement of brainstem systems. Importantly, we propose an integrated BIAF screener that brings about the prospect of a sensitive and reliable early life diagnostic scheme for weighing the risk for ASD. The BIAF screener could provide clinicians substantial gains in the future and may carve customized interventions long before the current DSM ASD phenotype is manifested using dyadic co-regulation of brainstem-informed autism markers.

Olfactory sensory and perceptual evaluation in newborn infants: A systematic review

Fetuses are able to process olfactory stimuli present in the womb and continue to show a preference for these odors for months after birth. Despite the accumulated knowledge about their early ability to perceive odors, there is a lack of validated scales for odor response in newborns. The evaluation of reactions of the olfactory system to environmental stimuli in infants has been defined by methodological theoretical approaches of experimental and clinical assessment tools. These approaches are mainly based on psychophysical approaches and predominantly use behavioral and physiological measures. Examples can be found in studies describing early abilities of newborn babies for behaviors or heart rate variability showing memory of maternal food preferences or mother's breast milk. This systematic review aimed to determine whether validated odor assessment tools can be feasibly used in studies. Particularly in light of the current COVID-19 pandemic and evidence of associated olfactory impairment resulting from SARS-COV-2 infection, the study is also motivated by the need for tools to assess olfactory function in neonates.

Protocol of controlled odorant stimulation for reducing apnoeic episodes in premature newborns: a randomised open-label Latin-square study with independent evaluation of the main endpoint (PREMODEUR)

INTRODUCTION

Apnoea affects 85% of premature infants under 34 weeks of age and would be an important risk factor for subsequent neuropsychological disorders. Currently, premature children with life-threatening apnoeas receive stimulants such as methylxanthines (mainly, caffeine) or doxapram (an analeptic unlicensed in children under 15). However, these products have undesirable effects (hyperarousal, irritability, sleep disorders, tachycardia) and are not always effective because apnoea does persist in some premature newborns. Previous studies have indicated that odorant stimulation, a non-invasive intervention, may stimulate the respiratory rhythm. The objective of the present protocol is to reduce the occurrence of apnoeic episodes in premature newborns by controlled odorant stimulation added to current pharmacological treatments.

METHODS AND ANALYSIS

The project is a randomised open-label Latin-square trial with independent evaluation of the main endpoint. It will include 60 preterm neonates from two university hospital neonatal intensive care units over 2 years (2021-2023). Each newborn will receive no (S0), sham (S1) or real olfactory stimulation (S2) in random order. During S2, three distinct odorants (mint, grapefruit and vanilla) will be delivered successively, in puffs, over 24 hours. Mint and grapefruit odours stimulate the main and the trigeminal olfactory pathways, whereas vanilla odour stimulates only the main olfactory pathway. A statistical analysis will compare the incidence of apnoeic episodes during S1 versus S2 using a mixed effects Poisson model.

ETHICS AND DISSEMINATION

Ethical approval was obtained from the Comité de Protection des Personnes Île-de-France XI (# 2017-AO13-50-53). The results will be disseminated through various scientific meetings, specialised peer-reviewed journals and, whenever possible, posted on appropriate public websites.

TRIAL REGISTRATION NUMBER

NCT02851979; Pre-results.

Central Nervous System Processing of Floral Odor and Mother's Milk Odor in Infants

Newborns have a functioning sense of smell at birth, which appears to be highly significant for feeding and bonding. Still, little is known about the cerebral odor processing in this age group. Studies of olfactory function relied mostly on behavioral, autonomic, and facial responses of infants. The aim of the present study was to investigate central odor processing in infants focusing on electroencephalography (EEG)-derived responses to biologically significant odors, namely a food and a non-food odor. A total of 21 term-born, healthy infants participated (11 boys and 10 girls; age range 2-9 months, mean 5.3 ± 2.2 months). Odor stimuli were presented using a computer-controlled olfactometer. Breast milk was used as food odor. Farnesol was presented as a non-food odor. In addition, odorless air was used as a control stimulus. Each stimulus was presented 30 times for 1 s with an interstimulus interval of 20 s. EEG was recorded from 9 electrodes and analyzed in the frequency domain. EEG amplitudes in the delta frequency band differed significantly after presentation of food (breast milk) odor in comparison to the control condition and the non-food odor (farnesol). These changes were observed at the frontal recording positions. The present study indicates that central odor processing differs between a food and a non-food odor in infants. Results are interpreted in terms of focused attention towards a physiologically relevant odor (breast milk), suggesting that olfactory stimuli are of specific significance in this age group.

Effects of trans-2-nonenal and olfactory masking odorants on proliferation of human keratinocytes

Malodorous compounds induce stress responses, mood changes, an increase of skin conductance, activation of the sympathetic nervous system and other physiological changes, and it has been suggested that sensing malodors could provide warning of danger to health. Furthermore, the human body secretes various malodorous compounds as waste products of metabolism, including trans-2-nonenal ((E)-2-nonenal), the amount of which increases with aging. In the present study, we examined the effects of some endogenous malodorous compounds ((E)-2-nonenal, nonanal, pentanal, hexanal, hexanoic acid, hexylamine and isovaleric acid) on cultured human keratinocytes. (E)-2-Nonenal decreased the viability and promoted apoptosis of cultured keratinocytes. It also reduced the thickness and the number of proliferative cells in a three-dimensional epidermal equivalent model. Co-application of masking odorants (dihydromycenol, benzaldehyde, linalool, phenethyl alcohol, benzyl acetate and anisaldehyde), but not non-masking odorants (1,8-cineol, β-damascone, and o-t-butylcyclohexyl acetate), reduced the effect of (E)-2-nonenal on keratinocyte proliferation, and restored the thickness and number of proliferative cells in a three-dimensional epidermal equivalent model.

Human neonates prefer colostrum to mature milk: Evidence for an olfactory bias toward the "initial milk"?

OBJECTIVES

Colostrum is the initial milk secretion which ingestion by neonates warrants their adaptive start in life. Colostrum is accordingly expected to be attractive to newborns. The present study aims to assess whether colostrum is olfactorily attractive for 2-day-old newborns when presented against mature milk or a control.

METHODS

The head-orientation of waking newborns was videotaped in three experiments pairing the odors of: (a) colostrum (sampled on postpartum day 2, not from own mother) and mature milk (sampled on average on postpartum day 32, not from own mother) (n tested newborns = 15); (b) Colostrum and control (water; n = 9); and (c) Mature milk and control (n = 13).

RESULTS

When facing the odors of colostrum and mature milk, the infants turned their nose significantly longer toward former (32.8 vs 17.7% of a 120-s test). When exposed to colostrum against the control, they responded in favor of colostrum (32.9 vs 16.6%). Finally, when the odor of mature milk was presented against the control, their response appeared undifferentiated (26.7 vs 28.6%).

CONCLUSIONS

These results indicate that human newborns can olfactorily differentiate conspecific lacteal fluids sampled at different lactation stages. They prefer the odor of the mammary secretion - colostrum - collected at the lactation stage that best matches the postpartum age of their own mother. These results are discussed in the context of the earliest mother-infant chemo-communication. Coinciding maternal emission and offspring reception of chemosignals conveyed in colostrum may be part of the sensory precursors of attunement between mothers and infants.

A network model of affective odor perception

The affective appraisal of odors is known to depend on their intensity (I), familiarity (F), detection threshold (T), and on the baseline affective state of the observer. However, the exact nature of these relations is still largely unknown. We therefore performed an observer experiment in which participants (N = 52) smelled 40 different odors (varying widely in hedonic valence) and reported the intensity, familiarity and their affective appraisal (valence and arousal: V and A) for each odor. Also, we measured the baseline affective state (valence and arousal: BV and BA) and odor detection threshold of the participants. Analyzing the results for pleasant and unpleasant odors separately, we obtained two models through network analysis. Several relations that have previously been reported in the literature also emerge in both models (the relations between F and I, F and V, I and A; I and V, BV and T). However, there are also relations that do not emerge (between BA and V, BV and I, and T and I) or that appear with a different polarity (the relation between F and A for pleasant odors). Intensity (I) has the largest impact on the affective appraisal of unpleasant odors, while F significantly contributes to the appraisal of pleasant odors. T is only affected by BV and has no effect on other variables. This study is a first step towards an integral study of the affective appraisal of odors through network analysis. Future studies should also include other factors that are known to influence odor appraisal, such as age, gender, personality, and culture.

Olfaction scaffolds the developing human from neonate to adolescent and beyond

The impact of the olfactory sense is regularly apparent across development. The fetus is bathed in amniotic fluid (AF) that conveys the mother's chemical ecology. Transnatal olfactory continuity between the odours of AF and milk assists in the transition to nursing. At the same time, odours emanating from the mammary areas provoke appetitive responses in newborns. Odours experienced from the mother's diet during breastfeeding, and from practices such as pre-mastication, may assist in the dietary transition at weaning. In parallel, infants are attracted to and recognize their mother's odours; later, children are able to recognize other kin and peers based on their odours. Familiar odours, such as those of the mother, regulate the child's emotions, and scaffold perception and learning through non-olfactory senses. During juvenility and adolescence, individuals become more sensitive to some bodily odours, while the timing of adolescence itself has been speculated to draw from the chemical ecology of the family unit. Odours learnt early in life and within the family niche continue to influence preferences as mate choice becomes relevant. Olfaction thus appears significant in turning on, sustaining and, in cases when mother odour is altered, disturbing adaptive reciprocity between offspring and carer during the multiple transitions of development between birth and adolescence. This article is part of the Theo Murphy meeting issue 'Olfactory communication in humans'.

A novel, short and easy-to-perform method to evaluate newborns' social olfactory preferences

Humans' early olfactory perception has been studied mainly within the framework of mother-offspring interactions and only a few studies have focused on newborns' abilities to discriminate body odors per se. The aim of this study was to develop a method to evaluate olfactory social preferences of infants at term-equivalent age. Twenty dyads of infants (10 born preterm and 10 born at term) at term-equivalent age and their mothers were included. We analyzed the behavioral reactions of infants to their mother's upper-chest odor (that bears social, non-food related information). The two impregnated gauzes and a control gauze were presented to the infants for 10 s each, in a random order. We compared two durations of gauze impregnation: 30 min and 12 h. This study reveals that mothers' upper chest emits sufficient olfactory information to induce reactions in infants born full-term or born preterm and that a short impregnation is preferable to evaluate their perception of body odors, notably for those born preterm.

Weanling Infants Prefer the Odors of Green Vegetables, Cheese, and Fish When Their Mothers Consumed These Foods During Pregnancy and/or Lactation

Infants' olfactory experience begins before birth and extends after birth through milk and complementary foods. Until now, studies on the effects of chemosensory experience in utero and/or through human milk focused on experimentally controlled exposure to only 1 target food bearing a specific odor quality and administered in sizeable amounts. This study aimed to assess whether early olfactory experience effect was measurable in "everyday conditions" of maternal food intake during pregnancy and lactation, and of infant intake at weaning, leading to expose the infant to corresponding odors as fetus, neonate, and infant up to 8 and 12 months of age. Infants' early food exposures were assessed by asking mothers to fill out diaries about their food consumption during pregnancy and breastfeeding, and about their infant's consumption during complementary feeding. To test odor liking, odorants representing a priori pleasant and unpleasant food odors, as well as odorless stimuli, were presented. The infant's exploratory behavior toward odorized bottles and nonodorized control bottles was measured in terms of mouthing duration, which is thought to reflect attraction and/or appetence. At age 8 months only, positive correlations were found between liking of some unpleasant odors and early exposure to these odors through mother's diet. No correlations were found between infants' liking of the pleasant odors and early exposures to the foods bearing these odors. This study highlights that early exposure to unpleasant food odors may increase subsequent liking (or reduce subsequent dislike) of these food odors at least until the age of 8 months.

Chemosensory Event-Related Potentials and Power Spectrum could be A Possible Biomarker in 3M Syndrome Infants?

3M syndrome is a rare disorder that involves the gene cullin-7 (CUL7). CUL7 modulates odour detection, conditions the olfactory response (OR) and plays a role in the development of the olfactory system. Despite this involvement, there are no direct studies on olfactory functional effects in 3M syndrome. The purpose of the present work was to analyse the cortical OR through chemosensory event-related potentials (CSERPs) and power spectra calculated by electroencephalogram (EEG) signals recorded in 3M infants: two twins (3M-N) and an additional subject (3M-O). The results suggest that olfactory processing is diversified. Comparison of N1 and Late Positive Component (LPC) indicated substantial differences in 3M syndrome that may be a consequence of a modified olfactory processing pattern. Moreover, the presence of delta rhythms in 3M-O and 3M-N clearly indicates their involvement with OR, since the delta rhythm is closely connected to chemosensory perception, in particular to olfactory perception.

fMRI-based Neuronal Response to New Odorants in the Newborn Brain

The sense of smell is one of the oldest and the most primitive senses mammals possess, it helps to evaluate the surrounding environment. From birth, smell is an important sensory modality, highly relevant for neonatal behavioral adaptation. Even though human newborns seem to be able to perceive and react to olfactory stimuli, there is still a lack of knowledge about the ontogeny of smell and the underlying central processing involved in odor perception in newborns. Brain networks involved in chemosensory perception of odorants are well described in adults, however in newborns there is no evidence that central olfaction is functional given the largely unmyelinated neonatal central nervous system. To examine this question, we used functional magnetic resonance imaging (fMRI) in the newborn to characterize cortical response to olfactory and trigeminal odorants. Here we show that brain response to odors can be measured and localized using functional MRI in newborns. Furthermore, we found that the developing brain, only few days after birth, processes new artificial odorants in similar cortical areas than adults, including piriform cortex, orbitofrontal cortex and insula. Our work provides evidence that human olfaction at birth relies on brain functions that involve all levels of the cortical olfactory system.

Sniffin' Away the Feeding Tube: The Influence of Olfactory Stimulation on Oral Food Intake in Newborns and Premature Infants

Because of their immaturity, many premature infants are fed via nasogastric tube. One objective of the neonatal care is to feed infants orally early. The olfactory function of premature infants is developed before birth and odorants have a significant impact on nutrition in infants. The aim of the study was to test whether odor stimulation has a positive effect on the transition from gavage to oral feeding in infants. Participants were premature infants with gestational age of more than 27 weeks, with full or partial gavage feeding, stable vital parameters and without invasive ventilation. Before each feeding procedure an odorant was presented in front of the infant's nose. Infants were randomized into 1 of 3 groups and received either rose odor (not food-associated), vanilla odor (food-associated), or placebo (no odor). The primary outcome of the study was defined as the time until complete oral nutrition. About 150 children born at a postnatal age of 9.5 ± 7.8 days were included in this study. The duration until complete oral nutrition was reached after 11.8 ± 7.7 (vanilla), 12.2 ± 7.7 (rose), and 12.9 ± 8.8 (control) days. A nearly linear relation between odor presentation frequency and effect size was detectable. For infants that received the intervention for more than 66.7% of the time the length of gavage feeding (8 ± 5.4) and hospitalization (11 ± 6.5) was significantly lower in the vanilla group when compared with control (15 ± 7.3 and 21 ± 13.7, respectively). Odor stimulation with vanilla has an impact on oral feeding in premature infants, however the odor has to be presented on regular basis.

A Proximal Perspective on Disgust

The functional basis of disgust in disease avoidance is widely accepted; however, there is disagreement over what disgust is. This is a significant problem, as basic questions about disgust require knowing if single/multiple forms/processes exist. We address this issue with a new model with one form of disgust generated by multiple processes: (a) pure disgust experienced during gastrointestinal illness; (b) somatosensory disgust elicited by specific cues that activate the pure disgust state; (c) anticipatory disgust elicited by associations between distance cues for somatosensory disgust and requiring threat evaluation; (d) simulated disgusts elicited by imagining somatosensory and anticipatory disgust and frequently involving other emotions. Different contamination processes interlink (a–d). The implications of our model for fundamental questions about disgust (e.g., emotion status; continuation into animals) are examined.

Is Frozen Human Milk That Is Refused by Mother's Own Infant Suitable for Human Milk Bank Donation?

Background: Infant refusal to feed previously frozen human milk is thought possibly attributable to lipase, an enzyme that cleaves fatty acids from milk triglycerides potentially changing the taste of the milk. Previous reports suggest that this milk is not harmful to infants; however, the lipase activity, macronutrient content, concentration of free fatty acids (FFAs), pH, and bacterial load of milk that meets this criterion are not fully understood. Objective: The objective was to determine whether refused frozen milk is different in composition from typical milk deposits received at a human milk bank. Methods: Frozen milk deposits previously refused by mother's own infant were collected from 16 mothers at five different time points when available (postpartum days 30, 60, 90, 120, and 150). Lipase activity, macronutrient composition, levels of FFA, pH, and bacteriology were determined. Analysis of mature donor milk and bacteriology data from the Ontario milk bank were used as controls. Results: The lipase activity for all samples was at or below literature values for mature human milk and lower compared with control milk (p < 0.001) for all time periods except at day 30. Macronutrient composition was not different from control values and did not change significantly over 150 days, with the exception of crude protein, which declined with milk maturity (p < 0.005). The pH for all postpartum time groups was lower (p < 0.02) in refused milk, and was inversely associated with lipase activity and FFA. FFA and bacterial counts were not different from control samples. Conclusions: Infant refusal of previously frozen milk may not be entirely due to endogenous lipase activity. This milk appears suitable for donation to human milk banks.

[The Effects of Breast Milk Olfactory Stimulation on Physiological Responses, Oral Feeding Progression and Body Weight in Preterm Infants]

PURPOSE

This study was conducted to evaluate the effect of breast milk olfactory stimulation on physiological responses, oral feeding progression, and body weight in preterm infants.

METHODS

A repeated measures design with nonequivalent control group was used. The participants were healthy, preterm infants born at a gestational age of 28~32 weeks; 12 in the experimental group and 16 in the control group. Data were collected prospectively in the experimental group, and retrospectively in the control group, by the same methods. Breast milk olfactory stimulation was provided 12 times over 15 days. The data were analyzed using the chi-square test, Mann-Whitney U test, Wilcoxon signed rank test and linear mixed models using SPSS 19.

RESULTS

The gastric residual volume (GRV) of the experimental group was significantly less than that of the control group. The heart rate, oxygen saturation, respiration rate, transition time to oral feeding, and body weight were not significantly different between the two groups.

CONCLUSION

These findings indicate that breast milk olfactory stimulation reduces GRV and improves digestive function in preterm infants without inducing distress.

The human newborn's umwelt: Unexplored pathways and perspectives

Historically, newborns, and especially premature newborns, were thought to "feel nothing." However, over the past decades, a growing body of evidence has shown that newborns are aware of their environment, but the extent and the onset of some sensory capacities remain largely unknown. The goal of this review is to update our current knowledge concerning newborns' perceptual world and how ready they are to cope with an entirely different sensory environment following birth. We aim to establish not only how and when each sensory ability arises during the pre-/postbirth period but also discuss how senses are studied. We conclude that although many studies converge to show that newborns are clearly sentient beings, much is still unknown. Further, we identify a series of internal and external factors that could explain discrepancies between studies, and we propose perspectives for future studies. Finally, through examples from animal studies, we illustrate the importance of this detailed knowledge to pursue the enhancement of newborns' daily living conditions. Indeed, this is a prerequisite for assessing the effects of the physical environment and routine procedures on newborns' welfare.

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.

The Face of Distaste: A Preliminary Study

Distaste is a primitive rejection impulse triggered by the ingestion of unpleasant tasting substances, many of which are toxic. Theoretical work has suggested that distaste may be the evolutionary precursor for both physical disgust, which serves to defend against disease and other threats to biological fitness, and moral disgust, which defends against threats to the social order. Consistent with this proposal, recent work has found that the facial expression of distaste may be similar to that of disgust. Specifically, raising of the upper lip has been reported in distaste, physical disgust, and moral disgust. However, competing evidence suggests that distaste and disgust expressions may differ, and the facial expressions of adult humans in response to distasteful stimuli remain poorly specified. To address this issue, we conducted a preliminary experiment to investigate the upper lip raise in adult volunteers (N = 15) as they tasted unpleasant, pleasant, and neutral liquids. We found increased raising of the upper lip for bitter and salty tastes relative to water and sweet, suggesting that the upper lip raise is indeed part of the distaste expression. Given evidence that the upper lip raise is also present in physical and moral disgust, these results are consistent with the proposed origins of disgust in distaste.

Development of a new in-home testing method to assess infant food liking

The objective of this study was to develop a new elaborate method to evaluate infants' liking of foods that could be applied at home and to compare the results of this elaborate method with those of a basic method. Mothers of infants aged 4 to 7 (n = 44) and 12-15 months (n = 46) participated in this study. For the basic method, mothers were asked to assess their infant's global liking at the end of a meal. Then, for the elaborate method, mothers received detailed instructions on how to feed their infant, how infants might express like/dislike and when to stop the meal. During the first nine spoons, they were asked to report the presence/absence of positive and negative behaviours after each spoon, and the infant's initial liking was reported after each triplet of spoons. They also assessed their infant's global liking at the end of the meal. Both methods were applied using three commercial familiar baby foods adapted to each age range. In 4-7-month-olds, the elaborate method showed a significant difference across products for liking, whereas the basic method did not show any difference. In 12-15-month-olds, the elaborate method showed more differences across products for liking than the basic method. In both age groups, negative behaviours, despite being less frequently reported, provided better liking discrimination than positive behaviours. In conclusion, the elaborate method produced better product liking discrimination than the basic method by focusing maternal attention on infants' eating behaviours since the first spoons.

Asians' Facial Responsiveness to Basic Tastes by Automated Facial Expression Analysis System

Growing evidence shows that consumer choices in real life are mostly driven by unconscious mechanisms rather than conscious. The unconscious process could be measured by behavioral measurements. This study aims to apply automatic facial expression analysis technique for consumers' emotion representation, and explore the relationships between sensory perception and facial responses. Basic taste solutions (sourness, sweetness, bitterness, umami, and saltiness) with 6 levels plus water were used, which could cover most of the tastes found in food and drink. The other contribution of this study is to analyze the characteristics of facial expressions and correlation between facial expressions and perceptive hedonic liking for Asian consumers. Up until now, the facial expression application researches only reported for western consumers, while few related researches investigated the facial responses during food consuming for Asian consumers. Experimental results indicated that facial expressions could identify different stimuli with various concentrations and different hedonic levels. The perceived liking increased at lower concentrations and decreased at higher concentrations, while samples with medium concentrations were perceived as the most pleasant except sweetness and bitterness. High correlations were founded between perceived intensities of bitterness, umami, saltiness, and facial reactions of disgust and fear. Facial expression disgust and anger could characterize emotion "dislike," and happiness could characterize emotion "like," while neutral could represent "neither like nor dislike." The identified facial expressions agree with the perceived sensory emotions elicited by basic taste solutions. The correlation analysis between hedonic levels and facial expression intensities obtained in this study are in accordance with that discussed for western consumers.

Responses of Human Neonates to Highly Diluted Odorants from Sweat

Conjugated forms of odorants contributing to sweat odor occur not only in human sweat but also in amniotic fluid, colostrum, and milk. However, it is unclear whether the released odorants are detected and hedonically discriminated by human newborns. To investigate this issue, we administered highly diluted solutions of (R)/(S)-3-methyl-3-sulfanylhexan-1-ol (MSH), (R)/(S)-3-sulfanylhexan-1-ol (SH), (E)/(Z)-3-methylhex-2-enoic acid (3M2H), and (R)/(S)-3-hydroxy-3-methylhexanoic acid (HMHA) to 3-d-old infants while their respiratory rate and oro-facial movements were recorded. Adult sensitivity to these odorants was assessed via triangle tests. Whereas no neonatal stimulus-specific response was found for respiratory rate, oro-facial reactivity indicated orthonasal detection of MSH and SH by male neonates, and of HMHA by the whole group of neonates. Dependent on the dilution of odorants, newborns evinced neutral responses or longer negative oro-facial expressions compared with the reference stimuli. Finally, newborns appeared to be more sensitive to the target odorants than did adults.

Food-Induced Emotional Resonance Improves Emotion Recognition

The effect of food substances on emotional states has been widely investigated, showing, for example, that eating chocolate is able to reduce negative mood. Here, for the first time, we have shown that the consumption of specific food substances is not only able to induce particular emotional states, but more importantly, to facilitate recognition of corresponding emotional facial expressions in others. Participants were asked to perform an emotion recognition task before and after eating either a piece of chocolate or a small amount of fish sauce-which we expected to induce happiness or disgust, respectively. Our results showed that being in a specific emotional state improves recognition of the corresponding emotional facial expression. Indeed, eating chocolate improved recognition of happy faces, while disgusted expressions were more readily recognized after eating fish sauce. In line with the embodied account of emotion understanding, we suggest that people are better at inferring the emotional state of others when their own emotional state resonates with the observed one.

Developmental Changes in Adolescents' Olfactory Performance and Significance of Olfaction

Aim of the current work was to examine developmental changes in adolescents' olfactory performance and personal significance of olfaction. In the first study olfactory identification abilities of 76 participants (31 males and 45 females aged between 10 and 18 years; M = 13.8, SD = 2.3) was evaluated with the Sniffin Stick identification test, presented in a cued and in an uncued manner. Verbal fluency was additionally examined for control purpose. In the second study 131 participants (46 males and 85 females aged between 10 and 18 years; (M = 14.4, SD = 2.2) filled in the importance of olfaction questionnaire. Odor identification abilities increased significantly with age and were significantly higher in girls as compared to boys. These effects were especially pronounced in the uncued task and partly related to verbal fluency. In line, the personal significance of olfaction increased with age and was generally higher among female compared to male participants.