11.1.1: Developmental Processes

Learning Objectives

1. Describe the process and purpose of synaptic pruning and when it typically occurs.
2. Define myelination.
3. Discuss how myelination supports cognitive and motor development.
4. Discuss the concept of brain plasticity and its impact on brain architecture and function, particularly in relation to early experiences.
5. Identify the importance of sensitive periods in early childhood.

Introduction

While most of the brain’s 100 to 200 billion neurons are present at birth, they are not fully mature, and during the next several years, dendrites, or connections between neurons, will undergo a period of transient exuberance or temporary dramatic growth.

Figure \(\PageIndex{1}\): Components of the neuron. Image by Martha Lally and Suzanne Valentine-French is licensed under CC BY-NC-SA 3.0

There is a proliferation of these dendrites during the first two years, so that by age 2, a single neuron might have thousands of dendrites. Following this dramatic increase, unused neural pathways will be eliminated, thereby strengthening those that are used.⁸ Because of this proliferation of dendrites, by age two, a single neuron might have thousands of dendrites.

Synaptogenesis, or the formation of connections between neurons, continues from the prenatal period, resulting in the formation of thousands of new connections during infancy and toddlerhood. This period of rapid neural growth is referred to as Synaptic Blooming.⁹ This activity is occurring primarily in the cortex, or the thin outer covering of the brain, involved in voluntary activity and thinking.

Figure \(\PageIndex{2}\): MRI scans of the human brain. Image is in the public domain.

The prefrontal cortex, located behind the forehead, continues to grow and mature throughout childhood and undergoes an additional growth spurt during adolescence. It is the last part of the brain to mature and will eventually comprise 85 percent of the brain’s weight. Experience will shape which of these connections are maintained and which of these are lost. Ultimately, about 40 percent of these connections will be lost (Webb, Monk, and Nelson, 2001). As the prefrontal cortex matures, the child becomes increasingly able to regulate emotions, plan activities, strategize, and make better judgments. Of course, this is not fully accomplished in infancy and toddlerhood but continues throughout childhood and adolescence.

Myelination

When babies are born, the myelin sheath—a fatty coating that insulates neurons and speeds up the transmission of electrical signals—does not fully cover all neurons in the nervous system.

Figure \(\PageIndex{4}\). Unmyelinated nerve, where axons are not completely covered, similar to how the sheath looks at birth. Image by Chiara Mazzasette is licensed CC BY 4.0.

Instead, myelination occurs rapidly throughout infancy and early childhood, continuing into adolescence (Lebel & Deoni, 2018). This process is crucial for efficient brain communication, supporting essential functions such as movement, sensory processing, and cognitive development. Research indicates that myelination is influenced by early experiences, including stimulation, nutrition, and social interactions, highlighting the importance of a rich and responsive environment in shaping brain development (García-Sierra & Kuhl, 2017). For example, children who read more typically develop greater myelination in areas of the brain associated with reading skills (Takeuchi et al., 2016).

Plasticity

The brain is highly adaptable, especially in the early years of life. This ability to change and reorganize in response to experiences is called plasticity. Early in development, plasticity allows the brain to form and strengthen the connections necessary for learning, problem-solving, and adapting to new environments (Kolb & Gibb, 2011). Because young children’s brains are still developing, they are particularly responsive to experiences, meaning both positive and negative environments can profoundly shape brain growth.

Synaptic Pruning

One of the most important processes in early brain development is synaptic pruning. During infancy and toddlerhood, the brain produces more neural connections (synapses) than it will ultimately need. By age three, a child’s brain has about twice as many synapses as an adult brain (Stiles & Jernigan, 2010). As a child interacts with their environment, the brain strengthens frequently used connections while gradually eliminating weaker or unused ones—a process known as synaptic pruning (Huttenlocher & Dabholkar, 1997). This process, which continues into early childhood and beyond, allows the brain to become more efficient, refining networks that support language, motor skills, and cognitive development.

Experiences

A key aspect of early plasticity, neural connections, and pruning is experience-expectant brain development. The brain is “wired” to expect certain universal experiences—such as hearing language, seeing light, and forming emotional bonds—and requires these experiences for typical development (Greenough et al., 1987). This is often referred to as a sensitive period, or critical period, in development (Levine & Munsch, 2024). For example, infants are born with the ability to recognize and process language sounds. Still, if they are not exposed to spoken language, their brain's capacity to develop strong language networks diminishes. This underscores the importance of rich, consistent, and nurturing experiences in early childhood, as the brain actively develops in response to its environment.

However, not all early experiences are positive. Trauma and chronic stress can disrupt the brain’s wiring process, affecting areas involved in emotional regulation, memory, and impulse control (Teicher et al., 2016). Early adversity, such as neglect or exposure to violence, can cause the brain to become hyper-responsive to stress, leading to long-term difficulties in managing emotions and behavior (Shonkoff et al., 2012). Fortunately, due to neuroplasticity, young children’s brains have the capacity to recover, especially when they receive responsive caregiving and supportive interventions (Nelson et al., 2019).

References, Contributors and Attributions

García-Sierra, A., & Kuhl, P. K. (2017). Neural networks for speech and language processing: Implications for neurodevelopmental disorders. Current Opinion in Neurobiology, 45, 13–20. https://doi.org/10.1016/j.conb.2017.01.013

Greenough, W. T., Black, J. E., & Wallace, C. S. (1987). Experience and brain development. Child Development, 58(3), 539–559. https://doi.org/10.2307/1130197

Huttenlocher, P. R., & Dabholkar, A. S. (1997). Regional differences in synaptogenesis in human cerebral cortex. The Journal of Comparative Neurology, 387(2), 167–178. https://doi.org/10.1002/(SICI)1096-9...19971020)387:2<167::AID-CNE1>3.0.CO;2-Z

Kolb, B., & Gibb, R. (2011). Brain plasticity and behaviour in the developing brain. Journal of the Canadian Academy of Child and Adolescent Psychiatry, 20(4), 265–276.

Lebel, C., & Deoni, S. (2018). The development of brain white matter microstructure. NeuroImage, 182, 207–218. https://doi.org/10.1016/j.neuroimage.2017.12.097

Levine, L. E., & Munsch, J. A. (2024). Child development from infancy to adolescence: An active learning approach (3rd ed.). Sage Publications.

Nelson, C. A., Zeanah, C. H., & Fox, N. A. (2019). How early experience shapes human development: The case of psychosocial deprivation. Annual Review of Psychology, 70, 173–197. https://doi.org/10.1146/annurev-psych-010418-103145

Shonkoff, J. P., Garner, A. S., Siegel, B. S., Dobbins, M. I., Earls, M. F., McGuinn, L., Pascoe, J., & Wood, D. L. (2012). The lifelong effects of early childhood adversity and toxic stress. Pediatrics, 129(1), e232–e246. https://doi.org/10.1542/peds.2011-2663

Stiles, J., & Jernigan, T. L. (2010). The basics of brain development. Neuropsychology Review, 20(4), 327–348. https://doi.org/10.1007/s11065-010-9148-4

Takeuchi, H., Sekiguchi, A., Taki, Y., Yokoyama, S., Yomogida, Y., Komuro, N., Yamanouchi, T., Suzuki, S., Kawashima, R., & Nakagawa, S. (2016). Training of working memory impacts structural connectivity. The Journal of Neuroscience, 30(9), 3297–3303. https://doi.org/10.1523/JNEUROSCI.4611-15.2016

Teicher, M. H., Samson, J. A., Anderson, C. M., & Ohashi, K. (2016). The effects of childhood maltreatment on brain structure, function, and connectivity. Nature Reviews Neuroscience, 17(10), 652–666. https://doi.org/10.1038/nrn.2016.111

8. Lifespan Development - Module 4: Infancy by Lumen Learning references Psyc 200 Lifespan Psychology by Laura Overstreet, licensed under CC BY 4.0
9. Lifespan Development - Module 4: Infancy by Lumen Learning references Psyc 200 Lifespan Psychology by Laura Overstreet, licensed under CC BY 4.0