Neuroscience of Cognitive Development

The Role of Experience and the Developing Brain

Charles A. Nelson, Kathleen M. Thomas, Michelle de Haan

• Publisher: Wiley
• Year: 2012
• Print ISBN: 9780471745860
• eBook ISBN: 9780471785101
• Edition: 1
• Topic: Psychology
• Subtopic: Developmental Psychology
• Index: Psychology

A new understanding of cognitive development from the perspective of neuroscience This book provides a state-of-the-art understanding of the neural bases of cognitive development. Although the field of developmental cognitive neuroscience is still in its infancy, the authors effectively demonstrate that our understanding of cognitive development is and will be vastly improved as the mechanisms underlying development are elucidated. The authors begin by establishing the value of considering neuroscience in order to understand child development and then provide an overview of brain development. They include a critical discussion of experience-dependent changes in the brain. The authors explore whether the mechanisms underlying developmental plasticity differ from those underlying adult plasticity, and more fundamentally, what distinguishes plasticity from development. Having armed the reader with key neuroscience basics, the book begins its examination of the neural bases of cognitive development by examining the methods employed by professionals in developmental cognitive neuroscience. Following a brief historical overview, the authors discuss behavioral, anatomic, metabolic, and electrophysiological methods. Finally, the book explores specific content areas, focusing on those areas where there is a significant body of knowledge on the neural underpinnings of cognitive development, including:
* Declarative and non-declarative memory and learning
* Spatial cognition
* Object recognition
* Social cognition
* Speech and language development
* Attention development
For cognitive and developmental psychologists, as well as students in developmental psychology, neuroscience, and cognitive development, the authors' view of behavioral development from the perspective of neuroscience sheds new light on the mechanisms that underlie how the brain functions and how a child learns and behaves.

Chapter 1

Brain Development and Neural Plasticity

A Précis to Brain Development

Before discussing the details of neural development, it is important to understand that brain development, at the species level, has been shaped over many thousands of generations by selective pressures that drive evolution. According to Knudsen (2003a), this portion of biological inheritance is responsible for nearly all of the genetic influences that shape the development and function of the nervous system, the majority of which have proven to be adaptive for the success of any given species. These influences determine both the properties of individual neurons and the patterns of neural connections. As a result, these selective pressures delimit an individual’s cognitive, emotional, sensory, and motor capabilities.

There is, however, a small portion of biological inheritance that is unique to the individual and results from the novel combination of genes that the child receives from the parents. Because there is no history to this gene pattern, any new phenotype that is produced has never been subjected to the forces of natural selection and is unlikely to confer any selective advantage for that individual. However, this small portion of biological inheritance is particularly important for driving evolutionary change, as novel combinations of genes or mutations that do confer a selective advantage will increase in the gene pool, while those that result in maladaptive phenotypes will die out (Knudsen, personal communication).

The brain develops according to a complex array of genetically programmed influences. These include both molecular and electrical signals that arise spontaneously in growing neural networks. By “spontaneously,” we mean signals that are inherent in the circuitry and are entirely independent of any outside influence. These molecular and electrical signals establish neural pathways and patterns of connections that are remarkably precise, and that make it possible for animals to carry out discrete behaviors beginning immediately after birth. They also underlie instinctive behaviors that may appear much later in life, often associated with emotional responses, foraging, reproduction (sex would fall under a social interaction), and social interactions. Beyond the scope of this chapter, but certainly worth investigating, is a consideration of which human behaviors fall into this category of “instinctive.” Our bias is that these are most likely going to be behaviors that have enormous implications for survival or reproductive fitness, such as the ability to experience fear in order to recognize a predator or to experience pleasure and, conversely, the reduction of displeasure in order to become attached to a caregiver. We should also acknowledge that it is extraordinarily difficult to study such behaviors in humans because the experimental manipulations that would need to be performed would be unethical (they would generally require selective deprivation). Hence our reluctance to claim that certain behaviors are “innate.”

To return to our discussion of nativism, there is no question that our genetic makeup has an enormous influence over who we are. To a large extent, human characteristics reflect evolutionary learning, which is exhibited in patterns of neural connections and interactions that have been shaped adaptively by evolution over thousands of generations. In addition to adaptive capacities, however, genetic mutations also can lead to deficits in brain function, such as impairments of sensation, cognition, emotion, and/or movement. We provide examples of both in subsequent sections of this chapter.

Genes specify the properties of neurons and neural connections to different degrees in different pathways and at different levels of processing. On the one hand, the extent of genetic determination reflects the degree to which the information processed at a particular connection is predictable from one generation to the next. On the other hand, because many aspects of an individual’s world are not predictable, the brain’s circuitry must rely on experience to customize connections to serve the needs of the individual. Experience shapes these neural connections and interactions but always within the constraints imposed by genetics.

BRAIN DEVELOPMENT

The construction and development of the human brain occurs over a very protracted period of time, beginning shortly after conception and depending on how we view the end of development, continuing through at least the end of adolescence (for overviews, see Figure 1.1 and Table 1.1). Before discussing brain development per se, we must first provide some background to embryology in general.

Figure 1.1 Overview to human brain development, beginning the 15th prenatal week and continuing to term and then the adult. This figure illustrates the dramatic changes (in surface structure) the brain undergoes during the 9 months of gestation. Source: From Central Nervous System, by O. E. Millhouse and S. Stensaas, n.d. Retrieved June 6, 2005, from http://www.medlib.med.utah.edu/kw/sol/sss/subj2.html.

Table 1.1 Neurodevelopmental Timeline from Conception through Adolescence

Developmental Event	Timeline	Overview of Developmental Event
Neurulation	18–24 prenatal days	Cells differentiate into one of three layers: endoderm, mesoderm and ectoderm, which then form the various organs in the body. The neural tube (from which the CNS is derived) develops from the ectoderm cells; the neural crest (from which the ANS is derived) lies between the ectodermal wall and the neural tube.
Neuronal migration	6–24 prenatal weeks	Neurons migrate at the ventricular zone along radial glial cells to the cerebral cortex. The Neurons migrate in an inside-out manner, with later generations of cells migrating through previously developed cells. The cortex develops into six layers.
Synaptogenesis	3rd trimester–adolescence	Neurons migrate into the cortical plate and extend apical and basilar dendrites. Chemical signals guide the developing dendrites toward their final location, where synapses are formed with projections from subcortical structures.
		These connections are strengthened through neuronal activity, and connections with very little activity are pruned.
Postnatal neurogenesis	Birth–adulthood	The development of new cells in several brain regions, including:
		—Dentate gyrus of the hippocampus
		—Olfactory bulb
		—Possibly cingulated gyrus; regions of parietal cortex
Myelination	3rd trimester–middle age	Neurons are enclosed in a myelin sheath, resulting in an increased speed of action potentials.
Gyrification	3rd trimester–adulthood	The smooth tissue of the brain folds to form gyri and sulci.
Structural development of the prefrontal cortex	Birth–late adulthood	The prefrontal cortex is the last structure to undergo gyrification during uterine life. The synaptic density reaches its peak at 12 months, however, myclination of this structure continues into adulthood.
Neurochemical development of the prefrontal cortex	Uterine life–adolescence	All major neurotransmitter systems undergo initial development during uterine life and are present at birth. Systems do not reach full maturity until late adulthood.

Source: From “Neurobiological Development during Childhood and Adolescence,” by T. White and C. A. Nelson, in Schizophrenia in Adolescents and Children: Assessment, Neurobiology, and Treatment, R. Findling and S. C. Schulz (Eds.), 2004, Baltimore, MD: Johns Hopkins University Press.

Embryonic Origins of Brain Tissue

Immediately after conception the two-celled zygote rapidly begins to divide into a many-celled organism. Approximately 1 week after conception has occurred, 100 cells have been formed (this clump of cells is referred to as a blastocyst). A series of molecular changes occur that lead to the rearrangement of these cells, with the subsequent creation of an inner and an outer cell mass. The inner mass (embryoblast) will give rise to the embryo itself, whereas the outer mass (trophoblast) will eventually give rise to all of the supporting tissues, such as the amniotic sac, placenta, and umbilical cord (see Figure 1.2).

Figure 1.2 As described in the text, the blastocyst is created by the mitotic process the zygote undergoes following conception. The blastocyst proper divides into an inner and outer layer, with the latter giving rise to the support structures (e.g., amniotic sac, umbilical cord, and placenta), whereas the former give rise to the embryo itself. Source: From Introduction to Child Development (6th ed.), by J. P. Dworetzky, 1996, St. Paul, MN: West Publishing Company.

Over the course of the next weeks, the cells comprising the embryo itself undergo a transformation, forming inner, middle, and outer layers. The inner layer of the embryo will go on to develop into the epithelial lining of the gastrointestinal and respiratory tracts; the parenchyma (outside portion) of the tonsils, thyroid gland, parathyroid glands, thymus, liver, and pancreas; the epithelial lining of the urinary bladder and most of the urethra; and the epithelial lining of the tympanic cavity, tympanic antrum, and auditory tube. Among others, the middle layer gives rise to cartilage, bone, connective tissue; striated and smooth muscles; heart, blood and lymph vessels, and cells; kidneys; gonads (ovaries and testes), and genital ducts; the membranes lining the body cavities (e.g., pericardial); and spleen. Finally, the outer layer of the embryo gives rise to the central (brain and spinal cord) and peripheral nervous system; the sensory epithelia of eye, ear, and nose; epidermis (or skin) and its appendages (hair and nails); mammary glands; pituitary gland and subcutaneous glands; enamel of the teeth; spinal, cranial, and autonomic ganglia; pigment cells of the dermis; the membranes covering the brain and spinal cord (meninges). The outer-most layer is the focus of attention in this book.

STAGES OF BRAIN DEVELOPMENT

Neural Induction and Neurulation

The process of transforming the undifferentiated tissue lining the dorsal side of the ectoderm (the outermost layer of the embryo) into nervous system tissue is referred to as neural induction. In contrast, the dual processes called primary and secondary neurulation further differentiate of this neural tissue into the brain and the spinal cord respectively (for recent review of neural induction and neurulation, see Lumsden & Kintner, 2003).

As Figures 1.3 and 1.4 illustrate, a thin layer of undifferentiated tissue is gradually transformed into an increasingly thick layer of tissue that will become the neural plate. Chemical agents collectively referred to as transforming growth factors are responsible for the subsequent transformation of this undifferentiated tissue into nervous system tissue (Murloz-Sanjuan & Brivanfou, 2002). Morphologically this is marked by a shift from the neural plate to the neural tube. The neural plate buckles, forming a crease down its longitudinal axis. The tissue then folds inward, the edges rise up, and a tube is formed. This process begins on approximately day 22 of gestation (Keith, 1948), with the tube fusing first at the midsection and progressing outward in either direction until approximately day 26 (Sidman & Rakic, 1982). The rostral portion of the tube eventually forms the brain and the caudal portion develops into the spinal cord (see Figure 1.4).

Figure 1.3 As discussed in the text, the inner cell mass gives rise...

Table of contents

• Cover
• Contents
• Title
• Copyright
• Preface
• Acknowledgments
• Introduction: Why Should Developmental Psychologists Be Interested in the Brain?
• Chapter 1: Brain Development and Neural Plasticity
• Chapter 2: Neural Plasticity
• Chapter 3: Methods of Cognitive Neuroscience
• Chapter 4: The Development of Speech and Language
• Chapter 5: The Development of Declarative (or Explicit) Memory
• Chapter 6: The Development of Nondeclarative (or Implicit) Memory
• Chapter 7: The Development of Spatial Cognition
• Chapter 8: The Development of Object Recognition
• Chapter 9: The Development of Social Cognition
• Chapter 10: The Development of Higher Cognitive (Executive) Functions
• Chapter 11: The Development of Attention
• Chapter 12: The Future of Developmental Cognitive Neuroscience
• References
• Index