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Chapter 5 reviews the brain circuits that regulate maternal behavior in nonhuman mammals. The medial preoptic area (MPOA) is essential for both the onset and maintenance of maternal behavior. Hormones and oxytocin act on the MPOA to stimulate the onset of maternal behavior. The neurotransmitters contained within MPOA neurons that may regulate maternal behavior are described, as are several neural inputs to the MPOA that regulate its output. A defensive neural circuit that inhibits maternal behavior in most virgin female mammals is described. MPOA output stimulates maternal behavior by depressing the defensive circuit while also activating neural circuits that underpin maternal motivation. MPOA output to the mesolimbic dopamine system is essential for appetitive maternal responses, while its output to the periaqueductal gray regulates consummatory responses. Synaptic plasticity within the MPOA-to-mesolimbic DA circuit is involved in the development of an enduring mother–infant bond.

Chapter 8 reviews the human parental brain. Most functional magnetic resonance imaging research has examined the maternal brain, with some research on the paternal brain. Although woman show allomaternal behavior, defensive neural circuits may depress maternal responsiveness under certain conditions. The subcortical circuits associated with human maternal behavior match those in nonhuman mammals and include medial preoptic area, mesolimbic dopamine, amygdala, and oxytocin neural systems. Interacting with these subcortical circuits are cortical regions, including dorsomedial prefrontal cortex and anterior insula, that are involved in maternal cognitions, empathy, emotions, and emotion regulation. The medial prefrontal cortex connects some of these cortical regions with the subcortical circuitry so that maternal cognitions and emotions can be translated into appropriate maternal behavior. The poor maternal behavior associated with postpartum depression may result from dysfunctions within these circuits, and alterations in corticotropin-releasing factor and OT may be involved.

Chapter 9 examines the development of the parental brain in animals, emphasizing that the way a mother treats her offspring affects their brain development and their subsequent maternal behavior, leading to an intergenerational continuity of maternal phenotypes. Two proposals are evaluated. First, maternal treatment influences the development of maternal motivation circuits in offspring. In support, the development of medial preoptic area projections to the mesolimbic dopamine system is affected. Second, maternal treatment influences the development of neural systems that regulate anxiety and stress reactivity in offspring. In support, the development of medial prefrontal cortex regulation of amygdala reactivity to stressful situations is affected. Deficient development of maternal motivation circuits may contribute to neglectful maternal behavior; deficient development of emotion regulation circuits may contribute to abusive maternal behavior. Epigenetics, particularly DNA methylation, and gene by environment interactions are involved in these processes.

Chapter 7 examines alloparental and paternal behavior. Although these behaviors are rare in mammals, their occurrence indicates that parental behavior can occur in the absence of pregnancy and parturition. For mammals of both sexes, dual brain circuits affect whether parental behavior occurs: An inhibitory defensive circuit (anterior hypothalamus/ventromedial hypothalamus projections to periaqueductal gray), and an excitatory parental circuit (medial preoptic area, mesolimbic dopamine system, and the oxytocin system). When alloparental behavior occurs, either through experimental genetic selection (virgin female laboratory house mice) or through natural selection (prairie voles, marmosets), the defensive circuit has been downregulated and the parental circuit has been upregulated by such selection. When paternal behavior occurs, either naturally (California mice, dwarf hamsters) or experimentally (laboratory rats and house mice), copulation with a female and remaining with her through parturition depresses the male’s defensive circuitry while activating his parental circuitry.