Chapter Introduction

CHAPTER 8

How Does the Nervous System Develop and Adapt?

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RESEARCH FOCUS 8-1 LINKING SOCIOECONOMIC STATUS TO CORTICAL DEVELOPMENT

8-1 THREE PERSPECTIVES ON BRAIN DEVELOPMENT

CORRELATING EMERGING BRAIN STRUCTURES WITH EMERGING BEHAVIORS

CORRELATING EMERGING BEHAVIORS WITH NEURAL MATURATION

IDENTIFYING INFLUENCES ON BRAIN AND BEHAVIOR

8-2 NEUROBIOLOGY OF DEVELOPMENT

GROSS DEVELOPMENT OF THE HUMAN NERVOUS SYSTEM

ORIGINS OF NEURONS AND GLIA

NEURONAL GROWTH AND DEVELOPMENT

CLINICAL FOCUS 8-2 AUTISM SPECTRUM DISORDER

UNIQUE ASPECTS OF FRONTAL LOBE DEVELOPMENT

GLIAL DEVELOPMENT

8-3 USING EMERGING BEHAVIORS TO INFER NEURAL MATURATION

MOTOR BEHAVIORS

LANGUAGE DEVELOPMENT

DEVELOPMENT OF PROBLEM-SOLVING ABILITY

EXPERIMENT 8-1 QUESTION: IN WHAT SEQUENCE DO THE FOREBRAIN STRUCTURES REQUIRED FOR LEARNING AND MEMORY MATURE?

A CAUTION ABOUT LINKING CORRELATION TO CAUSATION

8-4 BRAIN DEVELOPMENT AND THE ENVIRONMENT

EXPERIENCE AND CORTICAL ORGANIZATION

RESEARCH FOCUS 8-3 INCREASED CORTICAL ACTIVATION FOR SECOND LANGUAGES

EXPERIENCE AND NEURAL CONNECTIVITY

CRITICAL PERIODS FOR EXPERIENCE AND BRAIN DEVELOPMENT

ABNORMAL EXPERIENCE AND BRAIN DEVELOPMENT

HORMONES AND BRAIN DEVELOPMENT

CLINICAL FOCUS 8-4 ROMANIAN ORPHANS

GUT BACTERIA AND BRAIN DEVELOPMENT

INJURY AND BRAIN DEVELOPMENT

DRUGS AND BRAIN DEVELOPMENT

OTHER SOURCES OF ABNORMAL BRAIN DEVELOPMENT

CLINICAL FOCUS 8-5 SCHIZOPHRENIA

DEVELOPMENTAL DISABILITY

8-5 HOW DO ANY OF US DEVELOP A NORMAL BRAIN?

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Katherine Streeter

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RESEARCH FOCUS 8-1

Linking Socioeconomic Status to Cortical Development

Nobel Prize–winning American economist James Heckman has argued passionately about one effective strategy for economic growth: investing as early as possible in disadvantaged families promotes optimal development of young children at risk. Heckman notes that children from lower SES families typically develop gaps in knowledge and ability relative to their more advantaged peers.

These gaps influence health and prosperity, and they persist throughout life. Childhood SES correlates with cognitive development, language, memory, social and emotional processing, and ultimately with income and health in adulthood. One reason: early experiences related to SES influence children’s cerebral development.

To examine cerebral development, neuroimaging studies (as shown in Figure 8-14) visualize differences in brain development that relate to growing up in under-resourced environments. As the brain grows throughout childhood and adolescence, the cortical surface area expands before declining in adulthood (Schnack et al., 2014). Cortical surface area reflects the amount of neural tissue available for different behaviors and correlates positively with cognitive ability. It should be possible to estimate the effect of early experiences on brain and behavioral development by comparing the cortical surface area and cognitive abilities of people raised in lower or higher SES families.

Kimberly Noble and her colleagues (2015) used neuroimaging to investigate the relationship between SES and cortical surface area in more than 1000 participants aged 3 to 20. As shown in the illustration, lower family income, independent of race or sex, was associated with decreased cortical surface area in widespread regions of frontal, temporal, and parietal lobes, the regions shown in red.

The investigators also measured participants’ cognitive performance on tests of attention, memory, vocabulary, and reading. The larger the cortical surface area, the better the test outcomes. The negative effects of low SES were especially dramatic at the lower end of the family income spectrum, especially in families with annual incomes less than $30,000.

Low SES is associated with poor nutrition, high stress, and insufficient prenatal and infant care. Following on Heckman’s thesis, investing in children from low-income families will increase societal health and prosperity, because these children can optimize their brain development and realize their developmental potential. Policies aimed toward decreasing poverty can lead to clear improvements in children’s cognitive and brain development.

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After adjusting for age, sex, race, and parental education, Noble and colleagues associated family income with cortical surface area. Areal brain regions shown in red were significantly smaller in children from low-SES families.
Research from “Family income, parental education, and brain structure in children and adolescents” by K. G. Noble et al., 2015, NatureNeuroscience, online doi: 10.1038/nn.3983, Figure 2C, p. 4.

To see how scientists go about studying the interconnected processes of brain and behavioral development, think about all the architectural parallels between how the brain is constructed and how a house is built. House plans are drawn as blueprints; the plans for a brain are encoded in genes. Architects do not specify every detail in a blueprint, nor do genes include every instruction for brain assembly and wiring.

The brain is too complex to be encoded entirely and precisely in genes. This leaves the fate of billions of brain cells partly undecided, especially in regard to the massive undertaking of forming appropriate connections between cells.

If the structure and fate of each brain cell are not specified in advance, what controls brain development? Many factors are at work, and as with house building, brain development is influenced by the environment in the course of the construction phase and by the quality of the materials. As we saw in Research Focus 8-1, Linking Socioeconomic Status to Cortical Development, living in poverty can compromise children’s brain development.

We can shed light on nervous system development by viewing its architecture from different vantage points—structural, functional, and environmental. In this chapter, we consider the neurobiology of development first, explore behavioral correlates of developing brain functions next, then explore how experiences and environments influence neuroplasticity over the life-span.