There may be 4 major "inflection points" in the human brain

Brain function is by no means static throughout a person's life. From newborns to ninety-year-olds, human learning ability and the risk of cognitive decline are always in constant motion. Now, scientists may have discovered a potential cause of this phenomenon: at the four key age points of 9, 32, 66 and 83, the brain's neural connections may have undergone a major turn. On November 25, the relevant research results were published in Nature Communications.

Previous studies have shown that the human body experiences three rapid aging sessions around the age of 40, 60 and 80, but the complexity of the brain makes it more difficult to understand.

The brain is made up of different regions and exchanges information through white matter bundles. White matter bundles are filamentous structures made up of axons, thin protrusions that extend from neurons. These connections affect people's cognitive functions, such as memory. But it is not clear whether this neural connection changes significantly throughout life. Alexa Mousley of the University of Cambridge in the United Kingdom said: "No one has previously combined multiple indicators to describe the phased changes in the neural connections of the brain. ”

To fill this cognitive gap, Mousley's team analyzed MRI brain scan data from about 3,800 people in the UK and the United States. The participants were predominantly Caucasian and aged between 0 and 90 years. These scans are derived from a variety of brain imaging projects, most of which exclude people with neurodegenerative or psychiatric disorders.

The study found that brain connections in 90-year-olds usually go through 5 main stages, separated by 4 key turning points.

In the first stage, from birth to 9 years of age, the white matter bundles between regions of the brain appear to become longer or more curly, resulting in reduced transmission efficiency. "It takes longer for information to travel in different areas." Mousley said.

This may be because during infancy, the brain is filled with a large number of neural connections, but as they grow, unused connections are gradually "trimmed" off. Mousley analyzed that the brain seems to prioritize making a wide range of connections to accommodate skills such as playing the piano, but at the cost of reduced connection efficiency.

However, in the second stage, between the ages of 9 and 32, this pattern appears to reverse, likely stemming from the onset of puberty and the impact of hormonal changes on brain development. "At this time, the brain suddenly increases the efficiency of neural connections, they become shorter, and the speed of information transmission increases." Mousley notes that this may contribute to the development of skills such as planning and decision-making, as well as improved cognitive abilities such as working memory.

The third stage lasts the longest, from 32 to 66 years. "The brain is still changing at this stage, but to a much smaller extent." At this point, Mousley explains, the efficiency of connectivity between brain regions re-enters a period of gradual decline. "It's not clear exactly what drives this shift, but people in their 30s tend to be accompanied by a number of major changes, such as having children and living a stable life, which may all play a role." Katya Rubia of King's College London added that this could also be just a result of natural wear and tear on the body.

The researchers found that in the fourth stage, between the ages of 66 and 83, the connections between neurons in the same brain region appeared to be more stable than those between different brain regions. "It's interesting because the risk of developing dementia and developing health problems rises progressively at this stage." Mousley said.

In the fifth stage, between the ages of 83 and 90, the interregional connections gradually weaken and more information is transmitted through "hubs" connecting multiple regions. "This suggests that there are fewer resources to maintain connections at this stage, and the brain relies more on specific areas as hubs for connectivity." Mousley said.

Mousley notes that understanding these brain changes could help explain why mental illness usually flares up before age 25 and why people over 65 are particularly vulnerable to dementia.

"It's critical to understand the normal turning points in brain structure throughout a person's life so that we can explore abnormal changes that occur in mental health or neurodegenerative diseases," Rubia said. Once the abnormality is identified, the treatment plan can be accurately found. For example, you can explore which environmental factors or chemicals are causing the abnormality and find ways to reverse it through treatment, policy, or medication. ”

However, Rubia emphasized that further research is needed before that to verify whether these findings apply to more diverse populations.