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.
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. Mothers with high levels of cortisol were also found to be more vocal towards their children.
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 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.
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: Postpartum increase in gray matter volumes may help the mother activate the motivation to perform maternal behavior in response to cue from their offspring. In human mothers there was a correlation between increased gray matter volume in the
substantia nigra and positive emotional feelings towards the infant. Other changes such as
menstrual cycle,
hydration,
weight and
nutrition may also be factors which trigger the maternal brain to change during
pregnancy and
postpartum. Maternal experience alters behaviors which stem from the
hippocampus such as enhancing spatial navigation learning and behaviors linked with
anxiety. Importantly, less medial
prefrontal cortex activity and greater
limbic system activity (i.e.
entorhinal cortex and
hippocampus) were found among these post-traumatically stressed mothers of toddlers compared to mothers of toddlers without PTSD in response to stressful parent-child interactions as well as, within a different sample, in response to menacing adult male-female interactions. In the latter study, this pattern of corticolimbic dysregulation was linked to less observed
maternal sensitivity during mother-child play. Decreased ventral-medial prefrontal cortex activity in violence-exposed mothers, in response to viewing their own and unfamiliar toddlers in video-clips of separation versus play, has also been associated with increased PTSD symptoms,
parenting stress and decreased methylation of the glucocorticoid receptor gene.
Early experiences and shaping Women who had a positive experience involving their family in their childhood are more likely to be more
maternally sensitive and provide that same experience for their own children. Mothers that had negative experiences involving their families undergo neurobiological changes which lead to high
stress reactivity and
insecure attachment. This causes lower maternal responsiveness to their infant's needs. Rat mothers provide high levels of maternal care (licking and grooming) to their offspring if they themselves received high maternal care as a pup from their own mothers. Rat mothers who received low levels of maternal care as pups have lower levels of expression of the
glucocorticoid receptor gene and lower synaptic density in the
hippocampus. In human mothers, lower hippocampal volume has been associated with a lower ability to regulate emotions and stress, which can be linked with decreased
maternal sensitivity as a mother. Mothers with
insecure attachments to their own mothers display higher amygdala sensitivity to negative emotional stimuli, like hearing their infant cry. Having more difficulty dealing with stress makes mothers less responsive to their infant's cues. Larger gray matter and increased activations of the following brain areas occur in mothers who had experienced higher quality maternal care as infants:
Postpartum depression has also been associated with mothers who received low quality maternal care early in their own life. ==Paternal brain==