The human brain is not fully developed at birth and continues to develop and change throughout life. The most significant period of brain development occurs during the first few years of life, but the brain continues to grow and change throughout adolescence and into adulthood.
In this article, we will explore how the human brain develops through the lifespan in order to respond to the question: “When is the brain fully developed?”
Fetal Period
During the fetal period, the brain grows very rapidly and goes through a series of important developmental stages.
The fetal brain begins to develop during the third week of pregnancy, and the neural tube forms and begins to differentiate into the three primary brain regions: the forebrain, midbrain, and hindbrain. As development continues, these regions further differentiate into more specialized structures, such as the cerebral cortex and the cerebellum.
Starting at the ninth week of brain development, neural progenitor cells begin to divide and differentiate into neurons and glia—the two cell types that form the basis of the nervous system. By this point in development, the brain appears as a small, smooth structure.
From 15 to 20 weeks after conception, the number of cells in the cerebral cortex of a fetus increases rapidly. By seven months after conception(third trimester), the fetus is emitting its own brain waves, which can be detected through the mother’s abdomen.
When is the brain fully developed in a fetus?
During the fetal stage, the brain overgrows, and by the end of the second trimester (around 26 weeks of pregnancy), the brain has most of the basic structures that it will have at birth. However, these structures still need to be fully developed and will continue to mature and refine after birth.
Chilhood
During childhood, the brain continues to develop and change in response to various influences, environments, and experiences. Significant changes in the structure and function of the brain mark this period of brain development.
Infancy (0-2 years)
The brain undergoes rapid growth and development during the first few years of life. Important developmental milestones include:
- The maduration of the neural tube.
- The differentiation of neurons and glial cells.
- The establishment of the basic structure and function of the brain.
Early chilhood (2-6 years)
During this stage, the brain continues to grow and develop rapidly. Important developmental milestones include the development of language and communication skills, establishing social and emotional connections, and developing basic cognitive skills such as attention, memory, and problem-solving.
Middle chilhood (6-12 years)
During this stage, the brain continues to mature and develop. Critical developmental milestones include the development of higher cognitive skills such as abstract thinking and reasoning, self-control and impulse control, and the continued maturation of language and communication skills.
Synapses
A critical aspect of brain development in childhood is the formation of connections between neurons, known as synapses. For example, a child’s brain forms trillions of synapses in the first decade of life .
The number of synapses in the brain increases rapidly during the first few years of life and then declines around the age of 5 or 10. This process, called synaptic pruning, is thought to be a regular and essential part of brain development that helps the brain become more efficient by getting rid of unnecessary or underused connections.
Another important aspect of brain development in childhood is the maturation of the various brain regions. For example, the prefrontal cortex, which is involved in decision-making and impulse control, continues to mature throughout adolescence.
Adolescence
During the adolescent period (12 – 24 years), physical and emotional growth occurs simultaneously. While young people may be physically mature and ready to take on adult responsibilities, they also have a period of significant brain development and maturation, during which the brain undergoes several important changes.
Adolescents tend to be more impulsive and tend to seek out new experiences and strong emotions. For example, in Germany, it is estimated that over 60% of all deaths among adolescents aged 15-20 are due to traumatic injuries.
The prefrontal cortex in adolescence continues to mature into early adulthood. This process is essential for the development of executive functions such as planning, problem-solving, and impulse control.
Also, the synaptic pruning continues throughout adolescence but not as rapidly as during younger years. The total number of synapses stabilizes as the brain grows and becomes more efficient.
Adolescence is also when the brain becomes more sensitive to new experiences and is more open to learning and adapting to new situations. This process, known as plasticity, allows the brain to adapt and change in response to new experiences and can have a lasting impact on brain development.
However, the brain’s plasticity allows environmental influences to exert particularly strong effects on cortical circuitry. This makes intellectual and emotional development possible but also opens the door to potentially harmful influences.
Particular studies in adolescent brain development.
Functional imaging studies of children and adolescents have shown that their brains are more active than those of adults, and the amount of effective neural recruitment increases with age.
Studies have shown that adolescents have heightened activity in limbic areas when they are expecting something rewarding. For example, researchers found that adolescents have more activity in the nucleus accumbent than children or adults when they anticipate a reward.
Adulthood
The brain reaches its full size around the age of 12 in girls and around the age of 16 in boys, but this does not mean that it is fully developed at that point. In fact, the brain continues to develop throughout adulthood but is fully developed once people are in the range of their 30s and 40s.
One important aspect of brain development in adulthood is the process of neuroplasticity, which is the brain’s ability to adapt and change in response to new experiences. This process allows the brain to reorganize itself in response to new experiences and to form new connections between neurons.
Neuroplasticity can occur at any age, but it is thought to be more limited in older adults.
Another important aspect of brain development in adulthood is the process of neurogenesis, which is the formation of new neurons.
While neurogenesis is more active during development, it is thought to continue to a limited extent throughout life. Neurogenesis has been observed in certain areas of the adult brain, such as the hippocampus, which is involved in learning and memory.
Neurodevelopment continues throughout adulthood, supporting the prolonged emergence of adult functions and roles. Specifically, adulthood is marked by the development of association cortices and the front limbic systems involved in executive, attention, reward, and social processes.
The brain undergoes maturation from infancy to adulthood, undergoing sculpting and pruning of neurons and synapses. This can be seen in the decrease in gray matter (in red) in the cerebral cortex n the above image.
Conclusion
In this article, we have demonstrated that the human brain does not fully develop until adulthood. The reasoning behind this fact is simple: our brains are formed through experience, which we only get as we live. The experiences we collect through life shape us into the people we become. It should be no surprise that children aren’t capable of making important decisions with the same clarity as adults.
Bibliography
- L. Konkel, «The Brain before Birth: Using fMRI to Explore the Secrets of Fetal Neurodevelopment», Environ. Health Perspect., vol. 126, n.o 11, p. 112001, doi: 10.1289/EHP2268.
- S. Ackerman, The Development and Shaping of the Brain. National Academies Press (US), 1992. Accedido: 10 de enero de 2023. [En lÃnea]. Disponible en: https://www.ncbi.nlm.nih.gov/books/NBK234146/
-  «Bulletin #4356, Children and Brain Development: What We Know About How Children Learn – Cooperative Extension Publications – University of Maine Cooperative Extension», Cooperative Extension Publications. https://extension.umaine.edu/publications/4356e/ (accedido 10 de enero de 2023).
- «Synaptic Pruning: Definition, Early Childhood, and More», Healthline, 3 de enero de 2018. https://www.healthline.com/health/synaptic-pruning (accedido 10 de enero de 2023).
- K. Konrad, C. Firk, y P. J. Uhlhaas, «Brain Development During Adolescence», Dtsch. Ärztebl. Int., vol. 110, n.o 25, pp. 425-431, jun. 2013, doi: 10.3238/arztebl.2013.0425.