role of prolactin has been found to induce the maternal behavior in nulliparous rats exposed to a hypophysectomized steroid treatment as noted in which prolactin secreting pituitary implants were placed under the kidney capsule which caused a shortened latency to participate in maternal behavior towards foster pups. the functions of prolactin have been extensively studied on rats which has revealed its effects and profound role in maternal care. the role of prolactin has been found to induce the maternal behavior in nulliparous rats exposed to a hypophysectomized steroid treatment as noted in which prolactin secreting pituitary implants were placed under the kidney capsule which caused a shortened latency to participate in maternal behavior towards foster pups. a different study used non-hypophysectomized, steroid-treated nulliparous rats were exposed to a dopamine d2 agonist, called bromocriptine, used to decrease the release of prolactin. bromocriptine, in turn, consequently lowered the maternal behavioral tendency to foster the young pups. conversely, when bromocriptine was used in conjunction with prolactin, the maternal behavior returned. another experiment also utilized bromocriptine to inhibit the release of prolactin in mother rats who were lactating to their pups during a 2-5-day period. the inhibition of prolactin release appears to indicate a critical period of the development of prolactin mechanisms within the pups. one study demonstrated that a deficiency in prolactin during the postnatal period in rats has the potential to affect their maternal behavior. in this study bromocriptine-treated juvenile rats exhibited hyperactivity and distractibility from the pups during the maternal behavior test suggesting the importance of prolactin to promote maternal behavior. adult rats also treated with bromocriptine showed similar differences when exposed to pups as opposed to control rats that exhibited maternal tendencies towards the pups. it was determined that prolactin deficiency may lead to disruptions in maternal behavior in adulthood, affect the neural substrates that promote maternal behavior, and that behavioral deficits are not only caused by a developmental delay in the systems regulating maternal behavior. human females cortisol in human mothers is elevated during pregnancy. human mothers with elevated cortisol during pregnancy more easily recognized, and were more attracted to, their own infant's odors postpartum, but this did not affect maternal attitudes toward their infants. behaviorally, mothers with higher levels of cortisol postpartum displayed higher levels of affectionate approach. women with higher cortisol levels were also more alert and sympathetic to infant crying. fleming and colleagues discovered that there was variation in how cortisol affected mothers with only one offspring and those with more than one offspring. when cortisol levels were high, women with one offspring displayed more affectionate contact, and women with multiple offspring spent more time in caretaking activities. however, the authors did not report whether or not the two groups of women had significantly different levels of cortisol. if they were different, the specific levels of cortisol may be a contributing factor in the different behaviors. human males couvade syndrome, or sympathy pregnancy, is defined by masoni and colleagues as fathers having two or more pregnancy symptoms. human fathers with couvade syndrome have higher levels of prolactin, and cortisol levels than fathers without. cross-culturally couvade syndrome is associated with how close the mother and father are just prior to birth; in the postpartum period, these fathers invested more in direct care. increased paternal care is likely associated with offspring survival. a study on canadian fathers found that, just before the birth of their infant, the fathers had significantly higher prolactin and cortisol levels. the father's prolactin and cortisol levels correlated with the mothers, although her levels were significantly higher. this provides evidence for wynne and reburn's hypothesis that mothers may provide cues to the father to activate paternal care pathways. in a separate study, fathers with higher prolactin compared to other fathers responded more positively to infant crying. these levels also positively correlated with father experience. in the same study, cortisol levels in response to infant cries were negatively correlated with father experience. higher cortisol levels was associated with higher father alertness and responsiveness to infant crying. increased levels of cortisol in response to infant cries was greater in inexperienced fathers. comparison of cortisol and prolactin between species and sex the behaviors associated with elevated cortisol levels appears to be more related to whether or not the mother was pre or postpartum, however the behaviors varied across species. in multiple studies on nonhuman females across species, found that high levels of cortisol postpartum was linked to low levels of maternal care. however, when cortisol levels were high during pregnancy there was an increase in maternal care. this difference did not hold true for humans of females and first time fathers. increased cortisol levels in general increased maternal care. increased cortisol levels in first time human fathers correlated with an increase in responsiveness to their infant's crying, but not in fathers with more than one offspring. testosterone human females studies have been conducted that show an interaction between brain circuits that respond to baby-stimuli, such as infant cries, and testosterone and oxytocin pathways. it has been found that when acute amounts of testosterone and oxytocin are administered to nulliparous women exposed to infant cries, they cause decreased responses in the amygdala and increased insula and inferior frontal gyrus responses. the alterations in responses within those brain regions have been seen to induce maternal behaviors. as such, there is speculation that increasing the availability of testosterone and oxytocin alters the maternal brain to induce a non-aversive response to infant cries. nonhuman males the most commonly associated hormone with males is testosterone. it is believed to be the “anti-parental hormone”; it inhibits the activation of paternal mechanisms. in many cases testosterone levels decrease when fathers have or actively care for their infants in non-humans. however, testosterone can be converted into estradiol, which supports paternal behavior. testosterone is converted into estradiol through the process of aromatization. stated previously, with the repeated presence of pups to non-parental rats, caregiving mechanisms can inhibit other mechanism, like the avoidance mechanism; similar inhibitions occur in male marmosets. when male marmosets hold their infants, they did not have an increased testosterone response to novel females when they otherwise would. in other words, holding the infant inhibited the mating mechanisms. this could mean that caregiving supersedes mating in some situations. for example, it may be adaptive to continue to invest in your current offspring rather than potentially create another. human males multiple studies on fathers have shown that a reduction in testosterone results in increased responsiveness to infant cues and that fathers in general have lower testosterone than non-fathers. testosterone in human males decreases with the number of offspring human males have. however, human males with higher level testosterone had greater activation of neural mechanisms when interacting with their own infants, this may be due to the activation of a paternal protection mechanism. comparison of testosterone between species and sexes between species variation in behaviors associated with testosterone in biparental species was not noted. across species father experience was negatively correlated with testosterone and lower levels of testosterone was associate with an increase in care. testosterone is more commonly studied in males than females. however, one study on human females found that lower testosterone is associated with increased maternal care.