Parental brain

Parental experience, as well as changing hormone levels during pregnancy and postpartum, cause changes in the parental brain. Displaying maternal sensitivity towards infant cues, processing those cues and being motivated to engage socially with her infant and attend to the infant's needs in any context could be described as mothering behavior and is regulated by many systems in the maternal brain. Research has shown that hormones such as oxytocin, prolactin, estradiol and progesterone are essential for the onset and the maintenance of maternal behavior in rats, and other mammals as well. Mothering behavior has also been classified within the basic drives (sexual desire, hunger and thirst, fear, power/dominance etc.). Less is known about the paternal brain, but changes in the father's brain occur alongside the mother. Research on this topic is continuing to expand as more researchers examine fathers. Many of the brain regions and networks responsible for parental behavior are responsible for parental behavior in human fathers after having a child. Changes in hormones, brain activation and brain structure (mainly changes in gray matter) are seen in both human mothers and fathers, with hormonal changes beginning in both males and females before the birth of their children, with changes continuing to develop after the birth of children.

Maternal brain

Maternal hormonal effect Different hormone levels in the maternal brain and the overall well being of the mother account for 40%–50% of differences in the mother's attachment to her infant. Mothers experience a decrease in estrogen and an increase in oxytocin and prolactin caused by lactation, pregnancy, parturition and interaction with the infant.

Oxytocin The levels of oxytocin in the maternal brain correlate with maternal behaviors such as gazing, vocalization, positive affect, affectionate touch and other similar mother-infant relationship behaviors.

Estradiol and progesterone High mother-infant attachment correlates with a higher ratio of estradiol/progesterone at the end of pregnancy, than at the beginning.

Cortisol In the first few days after giving birth the levels of cortisol are high which correlates with maternal approach behavior and positive maternal attitudes. Mothers with high levels of cortisol were also found to be more vocal towards their children. Mothers who experienced adversity in their own childhood, had higher daily patterns of cortisol levels, and were less maternally sensitive.

Glucocorticoids Glucocorticoids are not essential for displaying maternal behaviors, but in mothers, the levels of glucocorticoids are elevated as to initiate lactation.

Neuroanatomy Different areas/structures of the brain are associated with different factors which contribute to maternal behavior. One's own infant acts as a special stimulus which triggers activation of different areas of the brain. These brain areas together allow for maternal behavior and related systems. The Medial Preoptic Area (MPOA) of the hypothalamus contains receptors for estradiol, progesterone, prolactin, oxytocin, vasopressin and opioids. All these hormones are involved in some way in activating maternal behavior in the brain. The following are other behavioral changes necessary for mothering that the MPOA is responsible for:

mother's affect (changes made by the amygdala, prefrontal cortex) stimulus salience (changes made by the amygdala and nucleus accumbens) attention (changes made by the nucleus accumbens and medial prefrontal cortex) memory (changes made by the nucleus accumbens and medial prefrontal cortex).

The amygdala and medial prefrontal cortex also contain receptors for the hormones which are most likely to be changing behavior at the time of pregnancy, and may be the sites where these changes occur. Increased activity has also been observed in the amygdala as the mother is responding to emotions seen in negative (fearful) faces, positive faces or familiar faces that her baby makes. Primate mothers with damage to the prefrontal cortex have also been associated with disrupted maternal behavior. The dorsolateral prefrontal cortex (DLPFC) plays a role in the attention, cognitive flexibility and working memory of the mother. It helps the mother identify infant cues. In any environment and efficiently, it allows for the decision-making and action planning process involved in attending to the infant's cues. The thalamus, parietal cortex, and brain stem serve for processing the smell, touch and vocalization associated with the infant.

Postpartum changes Changes in estrogen, oxytocin and prolactin in the early postpartum period cause changes in the structures of the maternal brain.

In animal mothers Postpartum, new neuron production is suppressed due to decreased levels of estrogen and increased levels of glucocorticoids in mother rats. Mother-infant interaction is also thought to suppress neurogenesis in the hippocampus postpartum in the rat maternal brain. Maternal experience increases neurogenesis in the subventricular zone (SBZ) which is responsible for producing the neurons of the olfactory bulb. Prolactin is the hormone which mediates the increase in neurogenesis in SBZ. In animals, structures of the mother's brain change postpartum due to the increased interaction of the mother with the infant. The volume of gray matter increases postpartum in the following brain regions:

bilateral hypothalamus amygdala substantia nigra globus pallidus. These changes in the brain may occur in order to promote appropriate mothering behavior. The mother's positive attitude towards the infant can be used as a predictor for the increase in gray matter in the above stated brain structures. Also in rats, the increased interaction with pups causes an increase in density in the MPOA. Postpartum increase in gray matter volumes may help the mother activate the motivation to perform maternal behavior in response to cue from their offspring. Postpartum, the substantia nigra activates positive responses to the pup stimuli via dopamine neurons.

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