Four Major Stages of Brain Development from Birth to Age 90

Our brain’s functionality isn’t static throughout our lives. We know that our capacity for learning and the risk of cognitive decline fluctuate from infancy to our 90s. Recently, scientists may have uncovered a possible reason for this change. The wiring of our brains seems to experience four key turning points at ages 9, 32, 66, and 83.

Previous studies indicate that our bodies undergo three rapid aging cycles around the ages of 40, 60, and 80. However, the complexity of the brain complicates our understanding.

The brain consists of distinct regions that communicate through white matter tracts. These tracts are wire-like structures formed by long, slender projections known as axons, which extend from neurons, or brain cells. These connections significantly influence cognitive functions, including memory. Nevertheless, it was uncertain if this substantial change in wiring transpires throughout one’s life. “No one has combined multiple metrics to characterize stages of brain wiring,” states Alexa Mousley from Cambridge University.

In an effort to bridge this knowledge gap, Maudsley and his team examined MRI scans of roughly 3,800 individuals from the UK and US, primarily white, spanning ages from newborns to 90 years. These scans were previously gathered as part of various brain imaging initiatives, most of which excluded individuals with neurodegenerative diseases or mental health issues.

The researchers discovered that the brain wiring of individuals reaching 90 years old typically progresses through five significant stages, separated by four primary turning points.

In the initial stage, from birth to age nine, the white matter tracts between brain areas seem to become longer, more intricate, and less efficient. “It takes time for information to travel between regions,” explains Mausley.

This may be due to the abundance of connections in our brains as young children. As we age and gain experiences, we gradually eliminate unused connections. Mausley notes that the brain prioritizes making broader connections, beneficial for activities like piano practice, though at the expense of efficiency.

However, during the second stage, from ages 9 to 32, this trend appears to reverse, potentially driven by the onset of puberty and hormonal shifts affecting brain development. “Suddenly, your brain’s connections become more efficient. Connections become shorter, allowing information to traverse more swiftly,” says Mausley. This could enhance skills such as planning and decision-making, along with improved cognitive abilities like working memory.

The third stage, which spans from 32 to 66 years, is the longest phase. “During this stage, the brain continues to change, albeit at a slower rate,” Mausley explains. Specifically, she notes that connections between regions have a tendency to become less efficient over time. “It’s unclear what exactly triggers this change; however, the 30s often involve significant lifestyle alterations, like starting a family, which may play a role,” she adds. This inefficiency might also stem from general physical wear and tear, as noted by Katia Rubia from King’s College London.

From ages 66 to 83, the connections between neurons in the same brain area tend to remain more stable than those among different regions. “This is noteworthy, especially as the risk of developing conditions like dementia increases during this period,” Mausley remarks.

In the final stage, from ages 83 to 90, connections between brain regions weaken and rely more frequently on “hubs” that link multiple areas. “This indicates that there are fewer resources available to maintain connections at this age, leading the brain to depend on specific areas to serve as hubs,” Mausley explains.

Understanding these alterations in the brain could provide insights into why mental health issues arise, typically before the age of 25, and why individuals over 65 are particularly vulnerable to dementia, she states.

“It’s vital to comprehend the normal stages of structural changes in the brain throughout the human lifespan, so future research can explore deviations that occur in mental health and neurodegenerative disorders,” Rubia notes. “Grasping the causes of these deviations can assist us in pinpointing treatment strategies. For instance, we might examine which environmental factors or chemicals are responsible for these differences and discover methods to counteract them through treatments, policies, and medications.”

Nevertheless, Rubia emphasizes the need for further research to determine whether these findings apply to a more ethnically and geographically diverse population.