What happens to human brain at all stages of life?

Science and Health

Are our brains sharpest when we are children? What happens to it when we reach 40? What about retirement age? Until recently, the answer to these questions was not clear. Growth charts that track metrics like height and weight give a relatively clear picture of the range of human physical development, but scientists know less about the major milestones of brain maturation.

To try and solve some of these mysteries, an international team of researchers collected brain scan data from multiple studies representing 101,457 brains at all stages of life. The youngest scanned in the study was a 16-week-old fetus; the oldest was 100 years old. Across this large data set, the scientists were able to discover some pretty amazing facts:

  • The thickness of the cerebral cortex, the wrinkled outer layer of the brain, peaks at about age two. This area is involved in processes such as perception, language and consciousness.
  • The volume of the gray matter, which represents the total number of brain cells, reaches its peak during childhood, at about the age of 7.
  • White matter, which is made up of the connections between neurons that allow areas of the brain to communicate quickly, is at its highest volume around age 30, and begins to decline in later adulthood.
One hemisphere of a healthy brain (L) is pictured next to one hemisphere of a brain of a person suffering from Alzheimer disease, at the Morphological unit of psychopathology in the Neuropsychiatry division of the Belle Idee University Hospital in Chene-Bourg near Geneva March 14, 2011. (credit: DENIS BALIBOUSE/REUTERS)

It is important to note that the study aims to give a broad picture of the maturation of the human brain, and does not constitute a personalized map for individual people. Jacob Seidlitz, study co-author and research scientist at the Lifespan Brain Institute at the Children’s Hospital of Philadelphia and the University of Pennsylvania, told The Washington Post that brain development changes as we age. He added that even different parts of the brain, such as areas involved in vision versus speech, reach their own milestones at different points in life.

While some of these structural components have been linked to behaviors, white matter has been linked to more efficient decision-making, for example, there are still more complex genetic, cellular, and functional changes underlying the large structural changes. And while the brain is mostly defined at birth, with the creation of new neurons, the way different parts of the brain communicate with each other changes throughout life. The good news is that, unlike other parts of the body, our brain is built to change throughout our lives, and to meet the challenges posed by each stage of life.

Infancy: From birth to two years old

During infancy, the brain of babies is like a sponge. The brain absorbs environmental information, especially from parents or caregivers. In the first year for example, babies can learn any language, but this ability quickly diminishes based on the sounds or signs they hear or see. This rapid adjustment is why it can be much more difficult to learn new languages ​​later in life, especially ones that differ from the mother tongue.

Important cellular and genetic processes also take place during this period. While most neurons are formed at birth, other types of brain cells such as glial cells develop and mature rapidly in the first years of life. Glial cells — which can help form synapses, insulate connections, deliver nutrients, and destroy pathogens in the brain — will continue to mature for several decades.

Childhood: 2 to 10 years old

From about 18 months to 2 years of age, the brain shifts towards learning, which includes both strengthening important connections and reducing unused connections. To help the brain prioritize certain experiences, more inhibitory connections develop, acting as brakes on information processing, across brain circuits.

To reduce connections, infants lose about half of these newly formed synapses in a process known as synaptic pruning. To strengthen the connections, myelination is created, the process in which nerve connections are wrapped and isolated by the protein. This process is especially important for children’s development because they learn to process emotions, interact in social settings and develop more complex communication skills.

Because there is so much bonding and reinforcement during childhood, the brain is especially sensitive to interactions with caregivers and others in their environment. Stress from trauma or neglect during this time can have very profound effects on the rest of the child’s brain development throughout life.

Adolescence: ages 10-19

Adolescence is considered a difficult age behaviorally. From about age 10 to 19, there are dynamic changes in the brain networks involved in learning how to process emotions and motivations around different experiences.

This increased sensitivity to the environment is reflected in another bout of synaptic pruning and extensive myelination, but especially in the circuits underlying emotion and reward. This is why teenagers are motivated to explore new experiences, no matter how dangerous or threatening they may be.

Parts of the human brain (Illustrative). (credit: Wikimedia Commons)

Young adults: 20 to 39

The mid-to-late 20s are often considered a sort of “peak” of brain development, or an example of when the brain “matured.” This myth is partly due to the fact that the volume of white matter, which contributes to the “speed” of information processing, reaches a high level at these ages. Neural networks are constantly being honed and adapted into young adulthood, especially those involved in rational thought and consideration of future consequences. However, the brain is by no means “finished” with its development, but operates with a different strategy.

As the brain progresses into the 30s and 40s, adult synaptic plasticity, or the ability of connections to strengthen or weaken in response to changes in activity, is thought to be reprioritized rather than reduced.

40 to 65

In the 40s and beyond, life shifts towards the challenging roles of adulthood – career, family care and giving to the next generation. Experiences such as community involvement, lifestyle choices, or exposure to stress or toxins can drastically affect brain development and aging. For example, a 50-year-old who is very social, regularly exercises, travels, or volunteers may have a “younger” brain than a 50-year-old who is largely isolated from others and rarely engages in enriching activities.

Studies show that older adults who engage in memory training tasks, crossword puzzles, and even video games can improve some cognitive functions, but the mechanisms underlying these findings are still unknown.

65 and above

Late in life, the brain does shrink in size and can begin to degenerate. However, older people also have the potential for greater wisdom built on a lifetime of experiences. Some researchers have suggested that the brain circuits associated with emotional processing and moral decision-making may be involved in different components of wisdom, although this research is still limited.

Either way, it is clear that aging and life wisdom do not receive the respect they deserve when it comes to brain function.