The neural and hormonal bases of human parental care.

As parents in modern western societies face increasing pressures that strain their ability to provide quality childcare, it is important to consider the neural and hormonal bases of sensitive and nurturing parenting. The topic has been explored systematically in non-human animals, and these studies have yielded a rich source of hypotheses for human studies. Considerable evidence links oxytocin (OT) with sensitive caregiving in both men and women, and with stimulatory infant contact in men and affectionate infant contact in women. Testosterone, on the other hand, decreases in men who become involved fathers, and testosterone may interfere with aspects of paternal care. In neuroimaging studies, exposing parents to child stimuli activates neural systems involved in understanding others' facial expressions (the putative mirror neuron system), others' feelings (anterior insula and thalamocingulate regions) and others' thoughts (dorsomedial prefrontal cortex), as well as reward systems involved in approach-related motivation (ventral tegmental area, substantia nigra, ventral striatum and medial orbitofrontal cortex), and systems involved with emotion regulation (lateral prefrontal cortex). There is some evidence that this activity can be attenuated in mothers who do not breastfeed, and mothers with post-partum depression, perhaps due in part to lower levels of OT exposure. On the other hand, there is evidence suggesting that high levels of oxytocin (OT) may enhance activation in some of these systems. For example, OT may stimulate dopamine release in the ventral striatum, rendering child stimuli more rewarding. A few recent studies have gone beyond merely describing neural correlates to establishing the functional significance of activation patterns by linking them with observed maternal behavior outside the scanner. The results of these studies suggest that there may be an optimal range of activation within certain neural systems, neither too high nor too low, that supports appropriate parenting. There is also mounting evidence that the very structure of the human brain is altered by the cognitive challenges inherent in learning how to parent. Given that human mothers typically receive help with childrearing, it will be important to begin studying the neural and hormonal bases of alloparental care, with a particular emphasis on fathers due to their increasing involvement in childcare in modern western societies.