The scent of cuteness-neural signatures of infant body odors

The smell of the own baby is a salient cue for human kin recognition and bonding. We hypothesized that infant body odors function like other cues of the Kindchenschema by recruiting neural circuits of pleasure and reward. In two functional magnetic resonance imaging studies, we presented infantile and post-pubertal body odors to nulliparae and mothers (N = 78). All body odors increased blood-oxygen-level-dependent (BOLD) response and functional connectivity in circuits related to olfactory perception, pleasure and reward. Neural activation strength in pleasure and reward areas positively correlated with perceptual ratings across all participants. Compared to body odor of post-pubertal children, infant body odors specifically enhanced BOLD signal and functional connectivity in reward and pleasure circuits, suggesting that infantile body odors prime the brain for prosocial interaction. This supports the idea that infant body odors are part of the Kindchenschema. The additional observation of functional connectivity being related to maternal and kin state speaks for experience-dependent priming.

A chemical signal in human female tears lowers aggression in males

Rodent tears contain social chemosignals with diverse effects, including blocking male aggression. Human tears also contain a chemosignal that lowers male testosterone, but its behavioral significance was unclear. Because reduced testosterone is associated with reduced aggression, we tested the hypothesis that human tears act like rodent tears to block male aggression. Using a standard behavioral paradigm, we found that sniffing emotional tears with no odor percept reduced human male aggression by 43.7%. To probe the peripheral brain substrates of this effect, we applied tears to 62 human olfactory receptors in vitro. We identified 4 receptors that responded in a dose-dependent manner to this stimulus. Finally, to probe the central brain substrates of this effect, we repeated the experiment concurrent with functional brain imaging. We found that sniffing tears increased functional connectivity between the neural substrates of olfaction and aggression, reducing overall levels of neural activity in the latter. Taken together, our results imply that like in rodents, a human tear-bound chemosignal lowers male aggression, a mechanism that likely relies on the structural and functional overlap in the brain substrates of olfaction and aggression. We suggest that tears are a mammalian-wide mechanism that provides a chemical blanket protecting against aggression.

An integrative review: Human chemosensory communication in the parent-child relationship

Body odors serve as signals of kinship, with parents exhibiting a preference for the scent of their infants, and vice versa. The reciprocal perception of body odors can promote bonding through two mechanisms. Firstly, as an indirect pathway, through associative chemosensory learning, which leads to changes in proximity-seeking behaviors. Secondly, as a direct pathway, by eliciting the display of positive emotions, thereby reinforcing the mutual bond. Both mechanisms weaken as the child undergoes development due to changes in body odor expression and perception. This comprehensive review provides an overview of the current literature on chemosignals in the parent-child relationship, highlighting their significance in facilitating dyadic communication throughout the developmental span. Furthermore, future research perspectives are outlined to gain a better understanding of these benefits and, on the long run, derive potential interventions to strengthen parent child attachment.

The effects of breast milk odor on the physiological and behavioral responses caused by venipuncture pain in term infants: A clinical trial study

BACKGROUND

Pain management is very important for infants who are unable to express it verbally. Pain control is one of the nursing actions and part of their duties. This study attempted to determine the effects of breast milk odor on the physiological and behavioral responses caused by venipuncture pain in full-term infants at an educational hospital.

MATERIALS AND METHODS

This randomized clinical trial study was carried out on 3-5 days' term and healthy babies with a gestational age of 34 weeks and later in the 9-Day Hospital of Torbet Heydariyeh, Iran, 2021. The sample size, taking into account the possibility of a 10% dropout of samples included 20 babies for each group and a total of 40 babies were selected by convenience sampling. To collect data, a checklist of demographic characteristics, a registration form for physiological responses, and the modified behavioral pain scale were used.

RESULTS

The results of this study showed that breast milk odor has a positive effect on behavioral responses (P < 0.001) and also a significant relationship was observed between the effects of breast milk odor and physiological responses percentage of oxygen uptake and pulse (P < 0.001). However, no significant relationship was observed between breast milk odor and breathing variables (P > 0.05).

CONCLUSIONS

According to the results, olfactory stimulation with breast milk during venous blood sampling showed positive effects on physiological responses and pain reduction in infants. Therefore, it is recommended to use soothing stimuli such as the smell of breast milk during painful procedures in babies.

Infant factors that impact the ecology of human milk secretion and composition-a report from "Breastmilk Ecology: Genesis of Infant Nutrition (BEGIN)" Working Group 3

Infants drive many lactation processes and contribute to the changing composition of human milk through multiple mechanisms. This review addresses the major topics of milk removal; chemosensory ecology for the parent-infant dyad; the infant's inputs into the composition of the human milk microbiome; and the impact of disruptions in gestation on the ecology of fetal and infant phenotypes, milk composition, and lactation. Milk removal, which is essential for adequate infant intake and continued milk synthesis through multiple hormonal and autocrine/paracrine mechanisms, should be effective, efficient, and comfortable for both the lactating parent and the infant. All 3 components should be included in the evaluation of milk removal. Breastmilk "bridges" flavor experiences in utero with postweaning foods, and the flavors become familiar and preferred. Infants can detect flavor changes in human milk resulting from parental lifestyle choices, including recreational drug use, and early experiences with the sensory properties of these recreational drugs impact subsequent behavioral responses. Interactions between the infant's own developing microbiome, that of the milk, and the multiple environmental factors that are drivers-both modifiable and nonmodifiable-in the microbial ecology of human milk are explored. Disruptions in gestation, especially preterm birth and fetal growth restriction or excess, impact the milk composition and lactation processes such as the timing of secretory activation, adequacy of milk volume and milk removal, and duration of lactation. Research gaps are identified in each of these areas. To assure a sustained and robust breastfeeding ecology, these myriad infant inputs must be systematically considered.

fNIRS neuroimaging in olfactory research: A systematic literature review

There are a number of key features which make olfaction difficult to study; subjective processes of odor detection, discrimination and identification, and individualistic odor hedonic perception and associated odor memories. In this systematic review we explore the role functional near-infrared spectroscopy (fNIRS) has played in understanding olfactory perception in humans. fNIRS is an optical neuroimaging technique able to measure changes in brain hemodynamics and oxygenation related to neural electrical activity. Adhering to PRISMA guidelines, results of this search found that generally the majority of studies involving healthy adult subjects observed increased activity in response to odors. Other population types were also observed, such as infants, individuals with autism, attention deficit hyperactivity disorder (ADHD), post-traumatic stress disorder (PTSD), mild cognitive impairment (MCI) and dysosmia. fNIRS coverage heavily favored the prefrontal cortex, temporal and parietal regions. This review finds that odor induced cortical activation is dependent on multiple factors, such as odorant type, gender and population type. This review also finds that there is room for improvement in areas such as participant diversity, use of wearable fNIRS systems, physiological monitoring and multi-distance channels.

Early Postpartum Maternal and Newborn Responses to Auditory, Tactile, Visual, Vestibular, and Olfactory Stimuli

OBJECTIVE

To compare maternal psychological well-being, newborn behavior, and maternal and newborn salivary oxytocin (OT) and cortisol before and after two maternally administered multisensory behavioral interventions or an attention control group.

DESIGN

Randomized prospective clinical trial.

SETTING

U.S. Midwest community hospital.

PARTICIPANTS

Newborns and their mothers (n = 102 dyads) participated. Mothers gave birth vaginally at term gestation and had no physical or mental health diagnoses. Newborns with low Apgar scores, receipt of oxygen, suspected infection, or congenital anomalies were excluded.

METHODS

Dyads were randomly assigned to the auditory, tactile, visual, and vestibular (ATVV) intervention, the ATVV with odor from a baby lotion (ATVVO), or the attention control (AC) Group. Maternal psychological well-being, newborn behavior, and endocrine responses (salivary cortisol and OT) were measured before and after the intervention.

RESULTS

Newborns in the ATVV and ATVVO groups exhibited increases in potent engagement behaviors (p < .0001 and p = .001, respectively). Newborns in the AC group exhibited a decrease in potent engagement (p = .013) and an increase in potent disengagement (p = .029). Mothers in the ATVVO group exhibited an increase in OT (p = .01) and the largest change in OT (p = .02) compared to mothers in the ATVV and AC groups. We noted no change in maternal psychological well-being or newborn endocrine responses.

CONCLUSION

Inclusion of an odor via lotion with a behavioral intervention (ATVV) influenced maternal OT more than the behavioral intervention alone. Newborns were behaviorally responsive to the interventions; however, endocrine measures were not associated with intervention changes.

Epigenetic Clock Deceleration and Maternal Reproductive Efforts: Associations With Increasing Gray Matter Volume of the Precuneus

Reproductive efforts, such as pregnancy, delivery, and interaction with children, make maternal brains optimized for child-rearing. However, extensive studies in non-human species revealed a tradeoff between reproductive effort and life expectancy. In humans, large demographic studies have shown that this is the case for the most part; however, molecular marker studies regarding aging remain controversial. There are no studies simultaneously evaluating the relationship between reproductive effort, aging, and brain structures. We therefore examined the associations between reproductive efforts (parity status, number of deliveries, motherhood period, and cumulative motherhood period), DNA methylation age (mAge) acceleration (based on Horvath’s multi-tissue clock and the skin & blood clock), and the regional gray matter volumes (obtained through brain magnetic resonance imaging (MRI) using voxel-based morphometry) in 51 mothers aged 27–46 years of children in early childhood. We found that increasing reproductive efforts were significantly associated with decelerated aging in mothers with one to four children, even after adjusting for the confounding effects in the multiple linear regression models. We also found that the left precuneus gray matter volume was larger as deceleration of aging occurred; increasing left precuneus gray matter volume, on the other hand, mediates the relationship between parity status and mAge deceleration. Our findings suggest that mothers of children in early childhood, who have had less than four children, may benefit from deceleration of aging mediated via structural changes in the precuneus.

Reduced prefrontal cortex response to own vs. unknown emotional infant faces in mothers with bipolar disorder

Motherhood involves functional brain adaptations within a broad neural network purported to underlie sensitive caregiving behavior. Bipolar disorder (BD) is associated with aberrant brain response to emotional faces within a similar network, which may influence BD mothers' sensitivity to infant faces. This functional magnetic resonance imaging (fMRI) study aimed to investigate whether mothers with BD display aberrant neural responses to own infant faces compared to healthy mothers. Twenty-six mothers with BD in remission and 35 healthy mothers underwent fMRI during which they viewed happy and distressed still facial photographs of their own and of unknown infants. After the scan, mothers viewed the pictures again on a computer screen and rated the intensity of infants' facial emotions and their own emotional response to infant face images. Mothers with BD displayed lower left dorsolateral prefrontal cortex (dlPFC) response compared to healthy mothers to own vs. unknown infant faces specifically and abnormal positive functional connectivity between the left and right amygdala and prefrontal regions. BD mothers further displayed stronger deactivation of precuneus and occipital regions to all happy vs. distressed infant faces. After the scan, they rated their infants' distress and own response to their infants' distressed faces less negatively than healthy mothers. Blunted dlPFC response and aberrant fronto-limbic connectivity while viewing own infant faces and less negative ratings of own infants' distress in BD mothers may affect their responses to their own infants in real-life mother-infant interactions.

Sampling, identification and sensory evaluation of odors of a newborn baby's head and amniotic fluid

For baby odor analyses, noninvasive, stress-free sample collection is important. Using a simple method, we succeeded in obtaining fresh odors from the head of five newborn babies. These odors were chemically analyzed by two-dimensional gas chromatography coupled with mass spectrometry (GC × GC-MS), and compared with each other or with the odor of amniotic fluid from the baby's mother. We identified 31 chemical components of the volatile odors from neonate heads and 21 from amniotic fluid. Although 15 of these components were common to both sources, there was an apparent difference in the GC × GC patterns between the head and amniotic fluid odors, so the neonate head odor might be individually distinct immediately after birth. Therefore, we made artificial mixtures of the major odor components of the neonate head and maternal amniotic fluid, and used psychological tests to examine whether or not these odors could be distinguished from each other. Our data show that the artificial odor of a neonate head could be distinguished from that of amniotic fluid, and that the odors of artificial head odor mixtures could be correctly discriminated for neonates within an hour after birth and at 2 or 3 days of age.

The Design Matters: How to Detect Neural Correlates of Baby Body Odors

Functional magnetic resonance imaging of body odors is challenging due to methodological obstacles of odor presentation in the scanner and low intensity of body odors. Hence, few imaging studies investigated neural responses to body odors. Those differ in design characteristics and have shown varying results. Evidence on central processing of baby body odors has been scarce but might be important in order to detect neural correlates of bonding in mothers. A suitable paradigm for investigating perception of baby body odors has still to be established. We compared neural responses to baby body odors in a new to a conventional block design in a sample of ten normosmic mothers. For the new short design, 6 s of continuous odor presentation were followed by 19 s baseline and 13 repetitions were performed. For the conventional long design, 15 s of pulsed odor presentation were followed by 30 s of baseline and eight repetitions were performed. Neural responses were observed in brain structures related to basal and higher-order olfactory processing, such as insula, orbitofrontal cortex, and amygdala. Neural responses following the short design were significantly higher in comparison to the long design. This effect was based on higher number of repetitions but affected olfactory areas differently. The BOLD signal in the primary olfactory structures was enhanced by short and continuous stimulation, secondary structures did profit from longer stimulations with many repetitions. The short design is recommended as a suitable paradigm in order to detect neuronal correlates of baby body odors.

Neuroendocrinology and Adaptive Physiology of Maternal Care

Parental care is critical for offspring survival in many species. In mammals, parental care is primarily provided through maternal care, due to obligate pregnancy and lactation constraints, although some species also show paternal and alloparental care. These behaviors are driven by specialized neural circuits that receive sensory, cortical, and hormonal input to generate a coordinated and timely change in behavior, and sustain that behavior through activation of reward pathways. Importantly, the hormonal changes associated with pregnancy and lactation also act to coordinate a broad range of physiological changes to support the mother and enable her to adapt to the demands of these states. This chapter will review the neural pathways that regulate maternal behavior, the hormonal changes that occur during pregnancy and lactation, and how these two facets merge together to promote both young-directed maternal responses (including nursing and grooming) and young-related responses (including maternal aggression and other physiological adaptions to support the development of and caring for young). We conclude by examining how experimental animal work has translated into knowledge of human parenting, particularly in regards to maternal mental health issues.

Cortical thickness variation of the maternal brain in the first 6 months postpartum: associations with parental self-efficacy

The postpartum period is associated with structural and functional plasticity in brain regions involved in parenting. While one study identified an increase in gray matter volume during the first 4 months among new mothers, little is known regarding the relationship between cortical thickness across postpartum months and perceived adjustment to parenthood. In this study of 39 socioeconomically diverse first-time new mothers, we examined the relations among postpartum months, cortical thickness, and parental self-efficacy. We identified a positive association between postpartum months and cortical thickness in the prefrontal cortex including the superior frontal gyrus extending into the medial frontal and orbitofrontal gyri, in the lateral occipital gyrus extending into the inferior parietal and fusiform gyri, as well as in the caudal middle frontal and precentral gyri. The relationship between cortical thickness and parental self-efficacy was specific to the prefrontal regions. These findings contribute to our understanding of the maternal brain in the first 6 months postpartum and provide evidence of a relationship between brain structure and perceived adjustment to parenthood.

Activation of cortical and striatal regions during the expression of a naturalistic compulsive-like behavior in the rabbit

Nest building behavior in the pregnant rabbit (Oryctolagus cuniculus) can serve as a model for compulsions in obsessive compulsive disorder (OCD). Previous work showed that the "straw carrying" phase of nest building (during which the rabbit repeatedly collects straw in its mouth, carries it into the nest box and deposits it there, and then returns to collect more) is associated with increased c-FOS expression (a marker of neuronal activity) in the orbitofrontal, anterior cingulate, and piriform cortices. In the present study, we quantified c-FOS expression in the caudate and putamen, as well as in the primary motor, somatosensory, and prefrontal cortices of: (1) pregnant rabbits given straw (PREG + STRAW); pregnant rabbits not given straw (PREG); (3) estrous rabbits given straw (ESTROUS + STRAW); and (4) estrous rabbits not given straw (ESTROUS). We found that straw carrying was associated with increased c-FOS expression in the dorsal putamen, ventral caudate, primary motor cortex, and somatosensory cortex. Additionally, a correlational analysis of PREG + STRAW animals revealed that these regions, along with the premotor and prelimbic cortices, were significantly intercorrelated with respect to c-FOS expression, suggesting their "coactivation" during repetitive straw carrying. By contrast, behavioral interactions of non-pregnant (ESTROUS) rabbits with straw (e.g., sniffing, nibbling it) were associated with a distinct pattern of c-FOS expression that included the medial and ventral putamen. c-FOS expression in PREG + STRAW rabbits is similar to patterns of regional brain activity in OCD patients exposed to obsession-provoking stimuli, as well as to those observed in healthy human mothers responding to infant-associated stimuli.

Child Odors and Parenting: A Survey Examination of the Role of Odor in Child-Rearing

Parental caregiving is critical for the survival of our young and continuation of our species. In humans, visual and auditory signals from offspring have been shown to be potent facilitators of parenting. However, whether odors emitted by our young also influence human parenting remains unclear. To explore this, we conducted a series of questionnaire surveys targeting parents with children under 6 years old. First, we collected episodes on experiencing odors/sniffing various parts of a child’s body (n = 507). The prevalence of experiencing events described in those episodes was examined in a separate survey (n = 384). Based on those results, the Child Odor in Parenting scale (COPs) was developed, and subsequently used in the main survey (n = 888). We found COPs to have adequate content validity, concurrent validity, and reliability. Responses to the COPs demonstrated that parents, especially mothers with infants, are aware of odors from their offspring, and actively seek them in daily child-rearing. The factor structure and content of the COPs items indicated that child odors have both affective and instrumental roles. Affective experiences induce loving feeling and affectionate sniffing, while instrumental experiences pertain to specific hygienic needs. The head was the most frequent source of affective experiences, and the child’s bottom of instrumental. Each was experienced by more than 90% of the mothers with a child below 1 year of age. Affective experiences significantly declined as the child grew older, possibly associated with the decline of physical proximity between parents and child. This age-related decline was not prominent for instrumental experiences, except for the bottom, which significantly declined after 3 years of age. The present findings suggest that child odors play roles in human parenting, and that their nature and significance change during the course of a child’s development.

The higher temperature in the areola supports the natural progression of the birth to breastfeeding continuum

Numerous functional features that promote the natural progression of the birth to breastfeeding continuum are concentrated in the human female's areolar region. The aim of this study was to look more closely into the thermal characteristics of areola, which are said to regulate the local evaporation rate of odors and chemical signals that are uniquely important for the neonate's 'breast crawl'. A dermatological study of the areolae and corresponding intern breast quadrants was undertaken on the mothers of 70 consecutive, healthy, full-term breastfed infants. The study took place just after the births at the Policlinico Abano Terme, in Italy from January to February 2014. Temperature, pH and elasticity were assessed one day postpartum using the Soft Plus 5.5 (Callegari S.P.A., Parma, Italy). The mean areolar temperature was found to be significantly higher than the corresponding breast quadrant (34.60 ±1.40°C vs. 34.04 ±2.00°C, p<0.001) and the pH was also significantly higher (4.60±0.59 vs. 4.17±0.59, p<0.001). In contrast, the elasticity of the areolar was significantly lower (23.52±7.83 vs. 29.02±8.44%, p<0.003). Our findings show, for the first time, that the areolar region has a higher temperature than the surrounding breast skin, together with higher pH values and lower elasticity. We believe that the higher temperature of the areolar region may act as a thermal signal to guide the infant directly to the nipple and to the natural progression of the birth to breastfeeding continuum.

Chemical olfactory signals and parenthood in mammals

This article is part of a Special Issue "Chemosignals and Reproduction". In mammalian species, odor cues emitted by the newborn are essential to establish maternal behavior at parturition and coordinate early mother-infant interactions. Offspring odors become potent attractive stimuli at parturition promoting the contact with the young to ensure that normal maternal care develops. In some species odors provide a basis for individual recognition of the offspring and highly specialized neural mechanisms for learning the infant signals have evolved. Both the main and the accessory olfactory systems are involved in the onset of maternal care, but only the former contributes to individual odor discrimination of the young. Electrophysiological and neurochemical changes occur in the main olfactory bulb leading to a coding of the olfactory signature of the familiar young. Olfactory neurogenesis could also contribute to motherhood and associated learning. Parturition and interactions with the young influence neurogenesis and some evidence indicates a functional link between olfactory neurogenesis and maternal behavior. Although a simple compound has been found which regulates anogenital licking in the rat, studies identifying the chemical nature of these odors are lacking. Neonatal body odors seem to be particularly salient to human mothers who are able to identify their infant's odors. Recent studies have revealed some neural processing of these cues confirming the importance of mother-young chemical communication in our own species.

Always follow your nose: the functional significance of social chemosignals in human reproduction and survival

This article is part of a Special Issue "Chemosignals and Reproduction" Across phyla, chemosensory communication is crucial for mediating a variety of social behaviors, which form the basis for ontogenetic and phylogenetic survival. In the present paper, evidence on chemosensory communication in humans, with special reference to reproduction and survival, will be presented. First, the impact of chemosignals on human reproduction will be reviewed. Work will be presented, showing how chemosensory signals are involved in mate choice and partnership formation by communicating attractiveness and facilitating a partner selection, which is of evolutionary advantage, and furthermore providing information about the level of sexual hormones. In addition to direct effects on phylogenetic survival, chemosignals indirectly aid reproductive success by fostering harm protection. Results will be presented, showing that chemosensory communication aids the emotional bond between mother and child, which in turn motivates parental caretaking and protection, leading to infant survival. Moreover, the likelihood of group survival can be increased through the use of stress-related chemosignals. Stress-related chemosignals induce a stress-related physiology in the perceiver, thereby priming a fight-flight-response, which is necessary for an optimum adaption to environmental harm. Finally, effects of sexual orientation on chemosensory communication will be discussed in terms of their putative role in stabilizing social groups, which might indirectly provide harm protection and foster survival. An integrative model of the presented data will be introduced. In conclusion, an outlook, focusing on the involvement of chemosensory communication in human social behavior and illustrating a novel approach to the significance of chemosensory signals in human survival, will be given.