Development of the Parental Brain in Humans

Chapter 10 deals with the development of the parental brain in humans, emphasizing experiential influences on the intergenerational continuity of maternal behavior: A history of experiencing childhood maltreatment (CMT; maternal neglect and/or abuse) is associated with alterations in the development of the child’s parental brain, which may lead to subsequent deficits in its maternal behavior. The manner in which parents treat their children may affect the development of neural systems (a) that regulate emotionality, with poor parental care resulting in deficits in emotion regulation, and (b) that underpin maternal motivation, love, and empathy, with poor parental care decreasing these processes. Alterations in the development of medial prefrontal cortex, amygdala, mesolimbic dopamine, oxytocin, corticotropin-releasing factor, and serotonin neural systems are involved, as are epigenetic effects. Not all mothers who experience CMT become poor mothers, and the involvement of gene by environment interactions are highlighted.

Introduction

The introduction provides a brief overview of the book, describing its three major themes: (a) the mechanisms through which the brain regulates parental behavior in nonhuman mammals and parental cognitions, emotions, and behavior in humans; (b) the experiential and genetic factors that affect the development of the parental brain, with a focus on the intergenerational continuity of normal and abnormal parental behavior; and (c) an evolutionary perspective based on the fact that maternal behavior is the most basic mammalian caregiving system. It is proposed that the parental brain served as a foundation upon which natural selection acted to result in the evolution of other forms of strong prosocial behaviors in mammals, including humans.

Evolutionary Perspectives on the Parental Brain

Chapter 11 presents evolutionary perspectives on the parental brain. First, the evolution of neural modifications to the parental brain that may have allowed for the emergence of alloparental behavior is re-examined. Second, evidence is presented for the proposal that the parental brain provided the foundation or template for the evolution of other types of strong prosocial bonds in mammals, such as the pair bond that occurs in biparental monogamous species, and the hyper-cooperation and hyper-prosociality directed toward in-group members, as opposed to out-group members, that occur in human societies. With respect to the latter, neural mechanisms associated with alloparenting and cooperative breeding may have served as a preadaptation. Neural models, along with evidence, are presented to show how cortical and subcortical parental brain circuits may have been appropriated and utilized by natural selection to result in the evolution of high levels of prosociality within human social groups.

Development of the Parental Brain in Nonhuman Mammals

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.

The Parental Brain

The Parental Brain: Mechanisms, Development, and Evolution takes a three-pronged approach to the parental brain. The first part of the book deals with neural mechanisms. Subcortical circuits are crucially involved in parental behavior, and, for most mammals, the physiological events of pregnancy and parturition prime these circuits so that they become responsive to infant stimuli, allowing for the onset of maternal behavior at parturition. However, since paternal behavior and alloparental behavior occur in some mammalian species, alternate mechanisms are shown to exist that regulate the access of infant stimuli to these circuits. In humans, cortical circuits interact with subcortical circuits so that parental feeling states (emotions) and cognitions can be translated into parental behavior. The section on development emphasizes the experiential basis of the intergenerational continuity of normal and abnormal maternal behavior in animals and humans: The way a mother treats her infant affects the development of the infant’s brain and subsequent maternal behavior. Genetic factors, including epigenetic processes and gene by environment (G × E) interactions, are also involved. The chapter on evolution presents evidence that the parental brain most likely provided the foundation or template for other strong prosocial bonds. In particular, cortical and subcortical parental brain circuits have probably been utilized by natural selection to promote the evolution of the hyper-cooperation and hyper-prosociality that exist in human social groups. A unique aspect of this book is its integration of animal and human research to create a complete understanding of the parental brain.

The Parental Brain in Humans

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.

The Paternal Transition Entails Neuroanatomic Adaptations that are Associated with the Father’s Brain Response to his Infant Cues

The transition into fatherhood is a life-changing event that requires substantial psychological adaptations. In families that include a father figure, sensitive paternal behavior has been shown to positively impact the infant’s development. Yet, studies exploring the neuroanatomic adaptations of men in their transition into fatherhood are scarce. The present study used surface-based methods to reanalyze a previously published prospective magnetic resonance imaging dataset comprised of 20 first-time fathers (preconception-to-postpartum) and 17 childless men. We tested if the transition into fatherhood entailed changes in cortical volume, thickness, and area and whether these changes were related to 2 indicators of paternal experience. Specifically, we tested if such changes were associated with (1) the baby’s age and/or (2) the fathers’ brain activity in response to pictures of their babies compared with an unknown baby. Results indicated that first-time fathers exhibited a significant reduction in cortical volume and thickness of the precuneus. Moreover, higher volume reduction and cortical thinning were associated with stronger brain responses to pictures of their own baby in parental brain regions. This is the first study showing preconception-to-postpartum neuroanatomical adaptations in first-time fathers associated with the father’s brain response to cues of his infant.