Infant Brain Development: Stages, Tools & Parenting

Introduction

Brain development is a protracted process that continues through adolescence. Understanding the complexities involved in the development of the human brain—from the most primitive neural structure, the neural tube, which forms in the first weeks of pregnancy, to the complete adult brain with all its various functional regions—intrigues neuroscientists around the world. Born with more than 100 billion brain cells, which far exceed the number of stars in the Milky Way galaxy, the infant brain is one of the marvels of creation. Even more intriguing is the fact that each one of these neuronal cells is capable of forming connections with up to 15,000 neighboring cells, illustrating the extraordinary complexity of the brain's working mechanisms. Sean Brotherson argues that brain imaging studies, the main tools in the study and understanding of the human brain, have helped neuroscientists uncover some of these complexities over the last few decades. A brief overview of infant brain growth, its developmental stages, and the important tools used in studying the brain provides useful insight into this topic.

Infant Brain Development

The term "infant brain" refers to the developmental stage of the brain from birth through the first year of life. This period represents a uniquely important phase of rapid growth, characterized by the rapid multiplication of neurons and their supporting glial cells, as well as a proliferation of synapses—the connections between neurons through which information is communicated. The actual sequence of brain development is genetically programmed, and brain maturation proceeds from lower brain regions to higher regions. Nelson and Bloom (1997) found that most neuronal growth occurs during the early postnatal period, and it is also during this time that neuronal migration occurs within the brain.

One of the first changes in brain architecture observed in the postnatal period—particularly in the first few weeks after birth—is increased metabolic activity in the brain stem and the sensory motor cortex region. Since the brain stem controls vital functions such as heart rate, breathing, and other reflex actions, this region assumes developmental priority. Although the brain stem is well formed at birth, it continues to grow during the first few weeks and is also responsible for aspects of emotional and social development. Sean Brotherson notes that between 6 months and 1 year of age, the frontal cortex shows significant metabolic activity, indicating the development of higher cortical functions such as memory, concentration, and language.

A child's vision development continues throughout the first year of life. During this period, the number of neurons as well as the number of connections in the primary visual cortex is literally twice that observed in a fully mature adult human brain, as documented by Joan Styles. Critically, external visual stimulation is essential for the successful completion of primary visual cortex circuitry. Animal studies have confirmed that the absence of visual stimulus can irreversibly alter the functional organization of neuronal cells, leading to specific functional deficits. One early study by Hubel and Wiesel (1979) demonstrated that completely blocking one eye of a kitten resulted in permanent vision deficits in that eye. Thus, the first year is critical for the development of visual acuity, and children should be exposed to various colors, shapes, and objects at varying distances in order to establish the visual cortical circuitry.

The Role of Sensory Experience and Parental Interaction

Sean Brotherson also notes that studies on blind individuals reveal that the plasticity of the infant brain allows for reorganization of cortical regions to perform different functions. In blind children, for example, neurons in the primary visual cortex that are not used for visual processing were recruited by the primary auditory cortex to serve hearing functions. Functional MRI studies by Joan Styles have confirmed this cortical reorganization.

One recent study confirmed the importance of proper parental care and interaction during the first year of life. Miguel et al. (2006) reported that depressed and withdrawn mothers negatively affect the emotional and behavioral development of their infants. The researchers used EEG recordings to assess brain activity patterns among infants of depressed and non-depressed mothers. Infants of depressed mothers with a withdrawn interaction style exhibited greater right frontal EEG activation, while infants of non-depressed mothers with an active interaction style exhibited greater left frontal EEG activation. This asymmetry in EEG profile corresponds to specific neural activity patterns associated with "behavioral approach" and "behavioral withdrawal." A greater right-shift corresponded to inhibitory behavior, negative stimulus processing, and poor emotional regulation. Miguel et al. (2006) conclude that maternal depression negatively affects infant brain development and infant behavior.

Conclusion

Infant brain development is an important area of study for neuroscientists. The complex dynamic processes that underlie the development of the various functionalities of the infant brain and its maturation into an adult brain continue to be studied by researchers working to uncover the pattern of brain development. Earlier, there was considerable debate between the role of nature and nurture in a child's brain development. Today, neurologists have concurred that both nature and nurture play a significant role during the initial years of brain development. Advancements in neuroimaging techniques—including the various refinements in MRI and optical tomography—have made possible the focused study of the various developmental stages of the brain in infants. Particularly, the portable, safe, and easy-to-use optical tomography has brought the scanning device to the infant rather than requiring the infant to be transported to a fixed scanning device.