Infant Odors Research Articles

Pattern of fos activation in the ventral tegmental area (VTA) of male prairie vole’s (Microtus ochrogaster) in response to infant-related stimuli

Prairie voles are socially monogamous mammals that form pair bonds and display paternal care. This study was focused on the male prairie vole's neuronal responses to infant-related odors. Using the fos protein as a measure of neuronal activation, we examined the brain responses of males to infant-related odors. Prior to testing, the subjects had cohabited for two weeks with either a male sibling (Male-Cohabited) or an unrelated female (Female-Cohabited). Given that paternal behavior of male prairie voles is enhanced after two-weeks of cohabitation with a mate, we hypothesized that fos activation in brain regions involved in caring must be increased in response to infants or their odors but not in response to water or sub-adult odors. To test this hypothesis, we analyzed the pattern of fos expression in the ventral tegmental area (VTA) and the bed nucleus of the stria terminals (BNST) two hours after Male-Cohabited and Female-Cohabited males were exposed to either two live infants or to odors of infants, sub-adults or water. Results showed differences in fos expression within the VTA between Male-Cohabited and Female-Cohabited subjects that were exposed to infants and infant odors. The type of cohabitation had no effect on fos expression within the BNST, but the pattern of fos activation in this region differed by the type of odor to which the subjects were exposed. Together, the data indicate that female sensory cues during post-mating cohabitation may be processed within the VTA to direct the male prairie vole's responses towards infants.

Mother-child bonding is associated with the maternal perception of the child's body odor

Mothers can recognize the odor of their baby and typically adore this odor. In line with this observation, infant body odors activate reward-related brain areas in the mothers. In some mother-child-dyads however, the mutual bond is impaired and mothers have trouble engaging in interaction with their child. We aimed to examine how mothers with bonding difficulties perceive their child's body odor.In total, 75 mothers of babies aged 0–12 months were examined: Twenty-five of those were recruited in a psychosomatic day hospital ward, which is specialized for mother-child bonding disorders. Fifty age-matched healthy women and their babies served as controls. Body odor samples of each baby were collected from bodysuits in a highly standardized procedure. Thereafter, each mother rated the samples of her own and two other infants in a blind and randomized design. In addition, general olfactory function in terms of threshold and identification ability was tested and the mother reported the bonding to her baby in a standardized questionnaire.Healthy mothers showed a clear preference of their own compared to odors of other infant's, while mothers with bonding difficulties did not. Furthermore, the degree of preference was negatively correlated to self-reported bonding difficulties. Mothers with bonding difficulties could not identify their own infant's odor above chance, while control mothers could. Both groups did not differ in general olfactory function.We assume that reduced close body contact and interaction time associated with bonding difficulties may lead to reduced exposure and hinder the recognition of the infantile body odor. Within a vicious cycle, a reduced hedonic experience smelling their own baby may prevent women from deliberately approaching the baby. Thus, the positive and bond-building consequences of bodily and sensory interaction cannot unfold. As the baby's odor is normally perceived as very pleasant and rewarding, the conscious perception of the infantile body odor may be an additive therapeutic approach for mothers with bonding difficulties.

Maternal Prefrontal Cortex Activation by Newborn Infant Odors

Mothers are attracted by infant cues of a variety of different modalities. To clarify the possible neural mechanisms underlying maternal attraction to infant odor cues, we used near-infrared spectroscopy to examine prefrontal cortex (PFC) activity during odor detection tasks in which 19 mothers and 19 nulliparous females (nonmothers) were presented with infant or adult male odors. They were instructed to make a judgment about whether they smelled an odor during each task. We estimated the PFC activity by measuring the relative oxyhemoglobin (oxyHb) concentrations. The results showed that while detecting the infant odors, bilateral PFC activities were increased in mothers but not in nonmothers. In contrast, adult male odors activated the PFC similarly in mothers and nonmothers. These findings suggest that maternal activation of the PFC in response to infant odors explains a part of the neural mechanisms for maternal attraction to infant odors.

Do females influence paternal responsiveness in male prairie voles Microtus ochrogaster by increasing the salience of infant odors?

Abstract Male prairie voles become more responsive to infants following cohabitation with a female. Exposure to female sensory cues prior to offspring birth may influence male paternal tendencies by modifying his response to infant odors in particular or to odors in general. To test these hypotheses, males were housed with an unfamiliar female or a same-sex sibling for 13 days then examined for their response towards either live infants or infant-like inanimate objects covered with one of three odors: water, infant, sub-adult. We recorded the number of males that retrieved and manipulated the infants or odor-covered objects and measured the frequency and duration of time males spent attending to them or engaged in other non-social activities. Female-Cohabited males approached the container holding infant-odor covered objects faster than Male-Cohabited males, but showed no differences in time spent manipulating those objects. Males in both groups spent more time manipulating live infants than odor-covered objects. However, Female-Cohabited subjects were more likely to manipulate odor-covered objects as well as live infants than Male-Cohabited subjects. Additionally, the frequency of self-grooming in Female-Cohabited males was higher for water-covered objects compared to Male-Cohabited males. In presence of water and live infants, Female-Cohabited males groomed themselves with greater frequency than in presence of infant odor or sub-adult odor. The data suggest that female cues increase the male’s sensitivity to infant odors and enhance the salience of non-social odors.

Maternal status regulates cortical responses to the body odor of newborns

Studies in non-human mammals have identified olfactory signals as prime mediators of mother-infant bonding and they have been linked with maternal attitudes and behavior in our own species as well. However, although the neuronal network processing infant cues has been studied for visual and auditory signals; to date, no such information exists for chemosensory signals. We contrasted the cerebral activity underlying the processing of infant odor properties in 15 women newly given birth for the first time and 15 women not given birth while smelling the body odor of unfamiliar 2 day-old newborn infants. Maternal status-dependent activity was demonstrated in the thalamus when exposed to the body odor of a newly born infant. Subsequent regions of interest analyses indicated that dopaminergic neostriatal areas are active in maternal-dependent responses. Taken together, these data suggests that body odors from 2 day-old newborns elicit activation in reward-related cerebral areas in women, regardless of their maternal status. These tentative data suggests that certain body odors might act as a catalyst for bonding mechanisms and highlights the need for future research on odor-dependent mother-infant bonding using parametric designs controlling for biological saliency and general odor perception effects.

Differential endocrine responses to infant odors in common marmoset ( Callithrix jacchus) fathers

Olfactory cues can exert priming effects on many mammalian species. Paternally experienced marmosets, Callithrix jacchus, exposed to direct isolated olfactory contact with their own infant's scent show rapid decreases in testosterone levels within 20 min, whereas paternally inexperienced males do not. The following study tests whether there is a differential steroid response to exposure of infant scent from dependent infants (own and novel) and independent infants (own and novel). We examined the serum levels of estradiol, estrone, testosterone, dihydrotestosterone (DHT), and combined estrogens and androgens in eight male marmosets 20 min after exposure to isolated infant scent. Testosterone and androgen levels combined were significantly lower with exposure to own infant scent than a novel infant scent when the infants were at a dependent age but not at an independent age. Estrogen levels elevated significantly in response to own infant scent when the infants were at a dependent age but not at an independent age. These results suggest that marmoset fathers are more responsive to priming cues from related infants and hormonal responses from fathers are greatest when the infant is at a dependent age.

Rodent model of infant attachment learning and stress

Here we review the neurobiology of infant odor learning in rats, and discuss the unique role of the stress hormone corticosterone (CORT) in the learning necessary for the developing rat. During the first 9 postnatal (PN) days, infants readily learn odor preferences, while aversion and fear learning are attenuated. Such restricted learning may ensure that pups only approach their mother. This sensitive period of preference learning overlaps with the stress hyporesponsive period (SHRP, PN4-14) when pups have a reduced CORT response to most stressors. Neural underpinnings responsible for sensitive-period learning include increased activity within the olfactory bulb and piriform "olfactory" cortex due to heightened release of norepinephrine from the locus coeruleus. After PN10 and with the decline of the SHRP, stress-induced CORT release permits amygdala activation and facilitates learned odor aversions and fear. Remarkably, odor preference and attenuated fear learning can be reestablished in PN10-15 pups if the mother is present, an effect due to her ability to suppress pups' CORT and amygdala activity. Together, these data indicate that functional changes in infant learning are modified by a unique interaction between the developing CORT system, the amygdala, and maternal presence, providing a learning system that becomes more flexible as pups mature.

Adult depression-like behavior, amygdala and olfactory cortex functions are restored by odor previously paired with shock during infant's sensitive period attachment learning

Maltreatment from the caregiver induces vulnerability to later life psychopathologies, yet attraction and comfort is sometimes provided by cues associated with early life maltreatment. We used a rat model of early life maltreatment with odor–0.5 mA shock conditioning to produce depressive-like behaviors and questioned whether stimuli associated with maltreatment would restore emotional neurobehavioral function to control levels. Pups received daily novel odor–0.5 mA shock conditioning from postnatal day 8 to 12. This procedure produces a new maternal odor that controls pups’ attachment behaviors. In adulthood, either with or without the infant odor, animals received a Forced Swim Test, Sucrose Preference Test or assessment of amygdala and olfactory system functioning using field potential signal evoked by olfactory bulb paired-pulse electrical stimulation. Following neonatal odor–shock pairings, but not unpaired controls, adults without the odor present showed increased depression-like behavior in the Forced Swim Test and Sucrose Preference Test and a deficit in paired-pulse inhibition in amygdala and piriform (olfactory) cortex. All effects were brought to control levels when the infant conditioned odor was presented during behavioral and neural tests. The ability of cues associated with early life maltreatment to normalize behavior and amygdala activity suggests these cues provide adaptive value in adulthood.

Changes in response to odors during the reproductive period in male and female prairie voles (Microtus ochrogaster)

In prairie voles, Microtus ochrogaster (Wagner, 1842), the onset of parental caring differs by sex and reproductive condition. Maternal caring is displayed abruptly at parturition, whereas paternal caring intensifies gradually during the reproductive period. To determine if changes in odor responsiveness contribute to sex differences in onset of parental behavior, voles were given a choice to investigate various odors at different times during the reproductive cycle. Subjects were either sexually naïve or mated. Mated pairs cohabited until mid-gestation, late gestation, or 3 days postpartum. Voles crossed a tunnel to explore a row of three filter papers covered with infant odor, orange extract, or saline. Males and females exhibited different odor preferences. Males preferred infant odor to saline and orange extract, whereas females preferred infant odor and saline to orange extract. Mating changed the odor investigative behaviors in both males and females. Some voles vigorously manipulated odor-covered papers. The number of females manipulating the papers increased abruptly at late gestation. The number of males manipulating the papers was particularly high at mid-gestation and after the birth of young. Results suggest that mating and cohabitation in prairie voles influences odor responses in a sex-specific manner.

Stress and pain responses in rats lacking CCK 1 receptors

CCK involvement in stress- and pain-responsiveness was examined by studying the behavior of infant (11–12-days-old) and adult OLETF rats that do not express CCK 1 receptors. Infant odor- and texture-preferences were also assessed. We hypothesized that OLETF rats will show behavioral patterns similar to those previously observed after CCK 1 antagonist administration. Rate of separation-induced ultrasonic vocalization was significantly greater in OLETF compared to controls, in two separate studies. Infant pups of the two strains did not differ in odor- and texture-preference tests. OLETF rats showed consistently longer hot-plate paw-lift (as infants, in two separate studies) and paw-lick (as adults) latencies. Summary: OLETF pups vocalized in isolation more than controls and showed relative hypoalgesic responses, evident also in adulthood, in concordance with the pharmacological literature.

The Effects of Infant Cries and Odors on Sympathy, Cortisol, and Autonomic Responses in New Mothers and Nonpostpartum Women

Objective. To determine the biological correlates of maternal responsiveness in new mothers, comparisons were made between new mothers and nonpostpartum women on their affective, hormonal, and heart rate responses to infant cries and odors. Design. Eighty-six new mothers were divided into 3 groups: a cry group who listened to prerecorded cries of newborn infants (n = 27), an odor group who smelled the T-shirts previously worn by newborn infants (n = 28), and the nonstimulation control group (n = 31). Nonpostpartum women also listened to infant cries (n = 30) or no stimuli (n = 30). Salivary samples were taken at 3 time points: prior to and at 20 and 40 min after stimulus session onset. Heart rates were recorded throughout the stimulus session. Results. New mothers were more sympathetic and more alert in response to cries than nonpostpartum women. There were no differences in mothers' responses to odors and control stimuli. Multiparous mothers showed a greater difference in their sympathy to pain versus hunger cries than did primiparous mothers. Mothers who experienced greater sympathy in response to cries had higher baseline salivary cortisol levels and a higher heart rate; in comparison to mothers showing low sympathy, they also underwent a greater decline in cortisol concentrations over the stimulus period. Nonpostpartum women did not show these same affect - physiology relations. These relations were not affected by mothers' social, educational, or economic status, events at the childbirth, or sex of the infant. Conclusions. During the postpartum period, elevations in glucocorticoids and in heart rate facilitate mothers' nurturant and attentive responses to infants and their cues.

Cortisol, Hedonics, and Maternal Responsiveness in Human Mothers

New mothers are more attracted to the body odor of newborn infants than are nonmothers. In this study we investigated the relation of postpartum hormones and of prior experience with infants to this enhanced maternal attraction to infant odors. New mothers were asked to complete a hedonics task, using a pleasantness scale to provide an attraction score to different odorants presented on a cotton substrate in a 1-pt Baskin-Robbins container. Mothers were “blind” to the contents of the container. Participants also completed an extensive set of 100-item likert scales concerning their attitudes toward infants, care taking, own maternal adequacy, and other interpersonal relations. Mothers were videotaped interacting with their infants and provided salivary samples prior to the interaction. Salivary samples were assayed by radioimmunoassay (RIA) for salivary concentrations of cortisol, progesterone, and testosterone. Results show that first-time mothers with higher cortisol concentrations were more attracted to their own infant's body odor. Mothers with higher cortisol levels were also better able to recognize their own infants' odors. While cortisol was not related to attitudinal measures of maternal responsiveness, mothers with more prior experience interacting with infants exhibited both more attraction to infant odors and more positive maternal attitudes. Together, prior maternal experience and postpartum cortisol explain a significant proportion of the variance in mothers' attraction to newborn infant odors. These relations are discussed in terms of the variety of “meanings” cortisol could have during the postpartum period.

94. - Cortisol and maternal attraction to infant odor

94. - Cortisol and maternal attraction to infant odor

Postpartum factors related to mother's attraction to newborn infant odors

Hedonic responses to a variety of infant (general body, urine, and feces) and noninfant (lotion, cheese, and spice) odorants were compared in four groups of subjects: new mothers, mothers a 1-month postpartum, and female and male nonparents. Using standard scaling procedures, subjects rated each of the odorants twice on a scale from extremely unpleasant (-20.5) to extremely pleasant (+20.5). In addition, all subjects completed a set of attitude questionnaires, and mothers also answered a childbirth questionnaire and were observed while feeding their infants.

Mother's identification of their infant's odors

Human mothers can identify their infants by smell alone at 6 hours post partum after a single exposure to their babies. This ability persists to 48 hours post partum with no improvement with additional experience. Fathers were not able to make the same discrimination.