Skip to main content

Currently Skimming:


Pages 183-219

The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.


From page 183...
... In this context, it is essential to balance excitement about all the new learning with caution about the limits of what is understood today. This chapter about the developing brain focuses on the role of experience in early brain development.
From page 184...
... 4. Abusive or neglectful care, growing up in a dangerous or toxic environment, and related conditions are manifest risks for healthy brain development.
From page 185...
... The milestones of brain development from the prenatal period until school entry involve the development and migration of brain cells to where they belong in the brain, embellishments of nerve cells through the sprouting of new axons or by expanding the dendritic surface; the formation of connections, or synapses, between nerve cells; and the postnatal addition of other types of cells, notably glia. Fascination with the earliest stages of brain development is understandable.
From page 186...
... Within the neural tube, the innermost cells divide repeatedly, giving rise first to the cells that primarily become nerve cells, or neurons, and later giving rise to both neurons and the supportive tissue components called glia. Once the nerve cells are formed and finish migrating, they rapidly extend axons and dendrites and begin to form connections with each other, called synapses, often over relatively long distances.
From page 187...
... , and this makes density estimates very difficult to interpret. Thus, evidence available to date does not enable determination of how ubiquitous synapse overproduction and loss are in brain development generally or in humans specifically.
From page 188...
... 188 to in in a, , .E ,, ~ in o .
From page 189...
... and their collaborators (e.g., LeVay et al., 1980) demonstrated that as the physiological functioning of the visual cortex became more refined and precise, the anatomical synaptic connections were also refined.
From page 190...
... In fact, it seems likely that the greater potential for recovery from deprivation or damage that characterizes young animals probably reflects the availability of both mechanisms. Postnatal Neurogenesis We now need to add the possibility of postnatal neurogenesis the postnatal production of new nerve cells to the repertoire of mechanisms
From page 191...
... Neurochemistry of Early Brain Development The sending and receiving of messages in the nervous system depends on chemical messengers. A number of these chemical messengers affect gene expression in nerve cells in ways that have long-lasting effects on how nerves grow, respond to stimulation, and function.
From page 192...
... These growth factors are present in different quantities and locations at different points in development of the brain, regulated by genes involved in normal brain development. They also change in their concentration in response to nerve damage, playing a role in the brain's attempts to adapt to and restore functioning following trauma.
From page 193...
... This evidence promises to help explain how alterations in the environment early in life may have wide-ranging effects on brain development and may alter patterns of behavioral responding for children with different rearing histories.
From page 194...
... supports normal brain development, and abnormal experience (e.g., prenatal alcohol exposure, occluded vision) can cause abnormal neural and behavioral development (Black et al., 1998~.
From page 195...
... but have limited translations to humans, and on so-called experiments of nature, such as prenatal exposures that occur at different points in fetal development (discussed below) and research on children with sensory deficits, such as the case of deaf children who do not experience normal spoken language inputs, and children who have sustained brain
From page 196...
... Within these limitations, it is well known that a variety of environmental factors play a significant role in modulating early brain development. Some of the greatest insights have come from research on the detrimental consequences of early biological insults, deprivations, and stress.
From page 197...
... This research on complex environments certainly suggests that better
From page 198...
... The need for research that can illuminate how environments that exceed some minimal threshold of adequacy affect human brain development is especially needed, in light of the fact that most of the research on how experience affects the developing brain explores the detrimental consequences of harmful experiences. Early Biological Insults and the Developing Brain Research on early biological insults provides fundamental insights into the vulnerability and resilience of the developing central nervous system.
From page 199...
... that are developing at the time that the virus crosses the placental barrier. Because the development of most organs is largely complete by the end of the first trimester, fetal development during the second and third trimesters of pregnancy is relatively more protected from the negative effects of the rubella virus.
From page 200...
... The adverse effects of prenatal alcohol exposure are now so widely known and accepted that it is hard to believe that the first report was issued only 30 years ago. Fetal alcohol syndrome was first described in the English-language medical literature in 1973 (Tones and Smith, 1973~.
From page 201...
... in attempting to understand the effects of early biological insults is well illustrated by prenatal alcohol exposure. In general, the prenatal period appears to be distinguished by its sensitivity to a large array of harmful conditions.
From page 202...
... Exposure later in gestation generally does not produce such gross structural malformations but nonetheless kills nerve cells and interferes with synaptogenesis, formation of myelin, and other biochemical processes, including reduction of NMDA receptor binding in the hippocampus. Research with humans also shows that the timing of prenatal alcohol exposure has differential effects (Connor and Streissguth, 1996; Institute of Medicine, 1996; Jacobson et al., 1993, 1998; Sampson et al., 1994; Streissguth et al., 1996a, 1996b)
From page 203...
... Chronicity is another important factor in understanding the effects of early biological insults. In the case of prenatal alcohol exposure, it appears that the effects on the fetus worsen with successive pregnancies.
From page 204...
... , due to fortification of infant formula and cereal and increased breast-feeding, among other factors. However, poor and minority children are still at considerable risk for iron deficiency with or without anemia (Ogden, 1998~.
From page 205...
... Maximal transport of iron into the brain corresponds with the brain growth spurt, and iron deficiency during this period results in a deficit of brain iron in animal models. These observations suggest that the developing brain may be particularly vulnerable to the effects of this nutrient deficiency.
From page 206...
... Thus, in human studies, it can be exceedingly difficult to disentangle poor development and behavioral outcomes that are due to the biological exposure, from those due to the problematic environment. Prematurity and Early Brain Development One of the true marvels of human brain development is that an infant can be born prematurely in the early part of the third trimester and not only survive, but also achieve something resembling his or her potential in mental and motor behavior.
From page 207...
... recent research with toddlers suggests , , , . , , , _ , , that even low-risk preterm infants (those born between 27 and 34 weeks gestational age)
From page 208...
... on head growth and developmental outcome. Besides gestational age and socioeconomic status, the next most important factor in assessing risk of adverse neurological outcomes is the degree of illness of the infant during the newborn period.
From page 209...
... A more pernicious effect of extrauterine life on brain development in small preterm infants is the general problem of malnutrition. Neonatal illness not only predisposes preterm infants to definable adverse events (e.g., intraventricular hemorrhage, hypoxia)
From page 210...
... The risk emanates from both insults that arise during the course of illness in the premature infant and from interruptions of the provision of the expected substrates and environment apparently necessary for normal brain development. We have used examples for which there is a substantial literature (e.g., intraventricular hemorrhage)
From page 211...
... THE DEVELOPING BRAIN 2 The evaluation literature on these interventions offers good news about the capacity of early childhood programs, which emphasize individualized developmental care, as well as initiatives focused on parental coping and training in optimal parenting skills, to improve health outcomes and decrease developmental delays in premature infants. It thus appears that the developmental problems associated with prematurity and low birthweight can be mitigated by intervention.
From page 212...
... Stress and the Developing Brain Research on premature infants has provided substantial evidence of the importance of the caregiving environment for the baby's later progress. This theme emerges, as well, from research on animals regarding how stress affects the developing brain.
From page 213...
... THE DEVELOPING BRAIN 213 digestive system, break down fat stores making energy available to cells, and dampen activity of the immune system. Cortiso!
From page 214...
... Doing things to the nest that result in better organized maternal behavior results in infant rats that develop into less fearful, less stress-reactive adults, whereas doing things that disrupt maternal behavior results in more fearful and stress-reactive adult rats. Researchers have also shown that strains of rodents that are known to be more stress-reactive are characterized by maternal care that involves less licking and grooming (Liu et al., 1997; Meaney et al., 1996; Plotsky and Meaney, 1993~.
From page 215...
... In general, there is much to learn about the extent to which the neurological pathways between caregiving environments and dysfunctional behavior that are emerging in the animal literature apply to human offspring and about the effects of remedial experiences that attempt to enhance the development of children from early abusive and neglectful environments. In sum, neuroscience evidence from animal research is increasingly pointing to experiences of neglect, stress, and trauma within the caregiving environment as a source of compromised brain development.
From page 216...
... Beyond this evidence regarding detrimental influences on brain development, neuroscience offers few insights into how early environments can function to enhance development beyond what might otherwise be expected. The experiments with complex environments conducted on rats reveal the benefits of more enriched environments, indicate that younger
From page 217...
... In sum, the neuroscientific research on early brain development says that the young children warranting the greatest concern are those growing up in environments, starting before birth, that fail to provide them with adequate nutrition and other growth-fostering inputs, expose them to biological insults, and subject them to abusive and neglectful care. Children with undetected sensorimotor difficulties (whose developing brains may not receive the stimulation they need)
From page 219...
... In fact, active debates now characterize discussions of the extent to which parenting and the family environment affect child development (Harris, 1995, 1998; Rowe, 1994~. Our reading of 219


This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More information on Chapter Skim is available.