The most formative years of brain development in children occur prenatally and the first three years of life, before they are ready for preschool. Most current policies and services for young children and their families living in disadvantaged circumstances are viewed by policymakers and the public as investments in “school readiness.” This is an approach which can favor cognitive stimulation over the promotion of social and emotional well-being. Yet, the growing evidence from the biology of childhood adversity, focusing on brain development, suggests that the most vulnerable could benefit from more investment in being protected from stress and its consequences.
The proper measure of disadvantage is not necessarily family poverty or parental education, although these matter a great deal. Rather, the available scientific evidence suggests that parenting skills are the most important critical resource. There are indications that family environments in the United States have deteriorated over the past forty years. More children are being born into disadvantaged families with greater parenting challenges, while parents in wealthier families are investing more in their children than ever before.
The Prenatal Period
Pregnancy naturally, through its hormonal effects, dampens a mother’s sensitivity to stress. However, the greater the stress, the smaller this dampening effect, increasing the likelihood of poor birth outcomes. Elevated stress during pregnancy is associated with higher than normal levels of the hormone cortisol. And higher cortisol levels, along with stress-related inflammation, which plays a role in cortisol production, can adversely affect fetal brain and body development with long-term consequences. For example, children born to mothers with high levels of anxiety in the early second trimester of pregnancy have been found in middle childhood to have reduced grey matter in specific brain regions. Grey matter plays a large role in muscle control and sensory perception. These children also exhibit impaired executive functions. Executive functions, centered in the large, forepart of the brain (e.g., prefrontal cortex) and serving, in a sense, as the brain’s traffic control system, involve such things as our abilities to hold information in mind and use it, pause and think before acting, and adjust appropriately to change. Children with compromised executive functions have difficulty learning.
The incidence of elevated stress levels is higher among women who are disadvantaged as a result of low-income, teen pregnancy, and single parenting. Further, low, compared to middle income, adults tend to have smaller social networks and less social support to buffer themselves from the negative effects of stress.
Adverse short-term and long-term outcomes for children can also stem from nutritional deficiencies and substance use (smoking, drugs) during pregnancy, which occur more often among disadvantaged women. These conditions increase the likelihood of a baby being born low weight or prematurely. Low birth weight and prematurity are markers for impaired adaptive capacities and physical and mental health that may last. For example, smoking during pregnancy has been traced to significantly lower educational performance of children at the age of 8, as have lower birth weight and even births just slightly under the normal range for gestation.
Infancy and Toddlerhood
Because of rapid brain development in the first three years of life, disruptions to development caused by conditions in the child’s environment may have life-long health effects and impair overall functioning. Children who experience serious deprivation during infancy and toddlerhood have greater problems with their executive functions during middle childhood. They have particular difficulties with visual memory, attention, and learning. Higher levels of the stress hormone cortisol in the saliva of babies in disadvantaged households have been shown to predict worse executive functioning and IQ by age three.
Parental care is particularly important during infancy and toddlerhood. Secure attachment or a healthy bond between a child and his or her mother has been found to promote resilience. Three types of less secure attachment can contribute to ongoing problems for children that may follow them into adulthood. In resistant attachment, associated with lower levels of maternal competence, a child is easily distressed and difficult to comfort. In avoidant attachment, which is associated with maternal rejection, lack of affection and interest, the child does not want to be comforted. Disorganized attachment can happen with children whose mothers act in incoherent and threatening ways, creating confusion for the child.
In general, babies are less likely to be secure when their mothers are less sensitive to them. Diminished maternal sensitivity happens when mothers themselves have chronic difficulties with their own self-regulation. A chaotic home environment increases the risks of child abuse, neglect, and accidents, all leading causes of death for infants and toddlers.
In fostering proper development, the initiation of breastfeeding seems to matter less than its duration. Longer breastfeeding may not only support parent-child bonding, but it also has been found to be associated with higher language skills at age three and higher verbal and nonverbal IQ at school age.
Studies have shown that children in their first years from higher income homes produce about twice as many words as those from lower income homes. Very young children in higher income homes tend to get more language stimulation from their caregivers. Engaged fathers may be especially important in language development, since they are more likely than mothers to ask their children wh-questions, and wh-questions appear to be conducive to language development. Father engagement is more likely to be less in lower income families.
A slight majority of infants and toddlers is cared for exclusively by their parents, and this form of care, as well as care by relatives, is more common among poor families. Care outside the home may have an impact on cognitive development. Cognitive performance is higher for young children in high and medium quality child care settings; lower income families are more likely to use lower quality child care. Interestingly, for children from higher income, lower risk families, spending more time being cared for outside their home has been associated, in some research, with elevated cortisol levels, a stress response. For children in higher risk families, more time in out of home care has been associated with lower cortisol levels. Higher cortisol levels in young children have been found to predict a higher likelihood for the development of externalizing problems (e.g., acting out).
All in all, very young children who are subject to multiple economic and social stressors enter the preschool years with higher rates of emotional challenges related to fear and anxiety, disruptive behavior, and impairment in executive functions and self-regulation. And the state of a child’s executive functions and ability to self-regulate subsequently predict his or her success in acquiring the basic literacy and numeracy skills needed for academic learning.