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Early Brain Development in Children

Statistics | Milestones | When does the brain stop developing | Experience-dependent | Critical periods & Plasticity | Nature vs nurture | Early Years

Brain Development

Early childhood is a time of tremendous brain development. The young brain literally changes shape and size in response to everything encountered in the early years. New environments, life experiences, caretakers, and relationships can all affect the way complex brain circuits are wired. This network of synaptic connections will ultimately determine brain function and the development of behavior.


  • An infant’s brain at birth has roughly 86 billion brain cells (neurons)​1​, almost all the neurons the human brain will ever have​2​.
  • Although a newborn has about the same number of neurons as an adult, it has only 25% of the adult size.
  • Infant’s neurons are connected by only roughly 50 trillion neural connections, called synapses, whereas an adult brain has about 500 trillion of them​3​.
  • By age 3, the synaptic connections have grown to 1000 trillion.
  • A child’s brain volume reaches 90% completion roughly by age 5​4​.
  • During adulthood, the synaptic density will be half that of a toddler at age two.
Brain diagram with five different colors on different regions - early brain development and how many billions of neurons by age 2

Early Developmental Milestones

Here are some of the childhood development milestones:

  • Week 3 post-conception – neuron production begins in the fetal brain.
  • At birth – auditory system matures​5​.
  • 5 weeks – learning and memory formation.
  • 9 months – large motor skills.
  • 1 year 3 months – speech.
  • 1.5 years – fine motor skills.

When Does the Brain Stop Developing

On average, the brain stops developing around age 25. Although an individual’s brain growth trajectory can vary slightly, most people’s healthy brain development is complete in their mid-20s.

The prefrontal cortex is the last brain region to develop.

However, it doesn’t mean the brain stops changing.

Forming and changing interconnections in our brain is an ongoing process that takes place throughout our lives. But as we age, they do so at a much slower rate.

The experience-dependent brain

One of the most prominent characteristics of human brain development is synaptic pruning.

The network of synapses grows rapidly during the first year and continues to do so during toddlerhood.

Life experience will activate certain neurons, create new connections between neurons and strengthen existing connections, called myelination.

Unused connections will eventually be eliminated during synaptic pruning​6​.

Synaptic pruning is the neuronal process in which unused neurons and synapses are eliminated to increase efficiency in neuronal transmissions. This process occurs after synaptic growth between early childhood and puberty.

Because life experiences can literally shape the brain, babies can adapt flexibly to any environment they’re born into​7​.

But that also means what parents do or don’t do during the formative years can have a profound impact on the child’s healthy development – mental health and physical health.

A network of neuron synapses brain architecture - where synaptic pruning happens

Critical Periods & Plasticity

Within early childhood, developmental timing is also important. There are windows of time when different regions of the brain become relatively more sensitive to experiences.

This period of childhood brain development is called a critical period or sensitive period.

During a critical period, synaptic connections in certain brain regions are more plastic and malleable. Connections are formed or strengthened given the appropriate childhood experiences. After the critical period has passed, the synapses become stabilized and less plastic​8​.

For example, language learning is much easier for young children. They can learn a nonnative language and attain proficiency more easily before puberty. So the sensitive period for language development is from birth to before puberty.

Self-motivated learner
Have trouble motivating your child? Check out:

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Also See: Benefits of Sensory Play to Brain Development

hand waters small plant in soil - child development

Nature vs Nurture In Child Development

Besides influencing the development of brain architecture, early life experience has another significant impact on a child’s development.

A large amount of scientific evidence indicates that life experience can affect gene expression — how information in a gene is used (epigenetics) — in some cases by slowing or shutting the genes off, and in others by increasing their output​9​.

This is why identical twins are not carbon copies of each other.

Although their genes (DNA code) are identical, their epigenetic markers are different from birth and continue to diverge as they interact with the environment in distinctive ways.

Even more important, these epigenetic changes can be permanent and passed down from generation to generation.

In the age-old nature-versus-nurture debate, epigenetics offers a surprising middle ground.

Genes are profoundly important, but so are environmental factors.

Also See: Specific Learning Disability

The Early Years Matter

Childhood is a time of tremendous sensitivity, a time when experience bestows lasting effects​10​.

Quality experience in everyday experience is so important in the early years.

Developmental outcomes can be seriously impacted if kids are deprived of basic social and emotional nurturing in this developmental process.

This is confirmed by various research.

For example, studies show that differences in socioeconomic status (SES) can result in disparities in brain structure. Extreme poverty is associated with lower gray matter volume and academic achievement​11​.

brain in tree shape with leaves in the middle - When does the brain stop developing

Also See: Asynchronous Development Of A Gifted Child And Their Unique Needs

Final Thoughts on Brain Development

Neuroplasticity and epigenesis are two major cornerstones in understanding a child’s neurological and brain development in the early years.

While we don’t need to be perfect parents (and who can be?), good enough parenting can do a child tremendous good.

In particular, among the different parenting stylesauthoritative parenting is the best parenting style associated with the best outcome. Adverse childhood experiences (ACE), on the other hand, can lead to toxic stress and devastating consequences.

Early childhood education is also important to a child’s cognitive functions and growth. Finding good childhood care providers and choosing a quality preschool for your child can also benefit their development in the long term.


  1. 1.
    Azevedo FAC, Carvalho LRB, Grinberg LT, et al. Equal numbers of neuronal and nonneuronal cells make the human brain an isometrically scaled-up primate brain. J Comp Neurol. Published online April 10, 2009:532-541. doi:10.1002/cne.21974
  2. 2.
    Graham J. Children and Brain Development: What We Know About How Children Learn. Cooperative Extension Publications.
  3. 3.
    Gauvain M, Cole M. Readings on the Development of Children. 5th ed. Worth Publishers; 2008.
  4. 4.
    Lebel C, Walker L, Leemans A, Phillips L, Beaulieu C. Microstructural maturation of the human brain from childhood to adulthood. NeuroImage. Published online April 2008:1044-1055. doi:10.1016/j.neuroimage.2007.12.053
  5. 5.
    McMahon E, Wintermark P, Lahav A. Auditory brain development in premature infants: the importance of early experience. Annals of the New York Academy of Sciences. Published online April 2012:17-24. doi:10.1111/j.1749-6632.2012.06445.x
  6. 6.
    Tau GZ, Peterson BS. Normal Development of Brain Circuits. Neuropsychopharmacol. Published online September 30, 2009:147-168. doi:10.1038/npp.2009.115
  7. 7.
    Huttenlocher P. Synapse elimination and plasticity in developing human cerebral cortex. Am J Ment Defic. 1984;88(5):488-496.
  8. 8.
    Reh RK, Dias BG, Nelson III CA, Kaufer D. Critical period regulation across multiple timescales. Proceedings of the National Academy of Sciences. 2020;117(38):23242-23251. doi:10.1073/pnas.1820836117
  9. 9.
    Stiles J, Jernigan TL. The Basics of Brain Development. Neuropsychol Rev. Published online November 3, 2010:327-348. doi:10.1007/s11065-010-9148-4
  10. 10.
    Balbernie R. Circuits and circumstances: the neurobiological consequences of early relationship experiences and how they shape later behaviour. Journal of Child Psychotherapy. Published online January 2001:237-255. doi:10.1080/00754170110087531
  11. 11.
    Hair NL, Hanson JL, Wolfe BL, Pollak SD. Association of Child Poverty, Brain Development, and Academic Achievement. JAMA Pediatr. Published online September 1, 2015:822. doi:10.1001/jamapediatrics.2015.1475

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